fix: address review findings — input validation, exception handling, cleanup

Add argument validation to EllipseConverter.Convert for tolerance and
semi-axis parameters. Narrow bare catch in Extensions.cs spline method
to log via Debug.WriteLine. Remove unused lineCount variable from
SolidWorksBendDetectorTests.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

OpenNest.Core/Geometry/EllipseConverter.cs

@@ -0,0 +1,217 @@
+using OpenNest.Math;
+using System;
+using System.Collections.Generic;
+
+namespace OpenNest.Geometry
+{
+    public static class EllipseConverter
+    {
+        private const int MaxSubdivisionDepth = 12;
+        private const int DeviationSamples = 20;
+
+        internal static Vector EvaluatePoint(double semiMajor, double semiMinor, double rotation, Vector center, double t)
+        {
+            var x = semiMajor * System.Math.Cos(t);
+            var y = semiMinor * System.Math.Sin(t);
+
+            var cos = System.Math.Cos(rotation);
+            var sin = System.Math.Sin(rotation);
+
+            return new Vector(
+                center.X + x * cos - y * sin,
+                center.Y + x * sin + y * cos);
+        }
+
+        internal static Vector EvaluateTangent(double semiMajor, double semiMinor, double rotation, double t)
+        {
+            var tx = -semiMajor * System.Math.Sin(t);
+            var ty = semiMinor * System.Math.Cos(t);
+
+            var cos = System.Math.Cos(rotation);
+            var sin = System.Math.Sin(rotation);
+
+            return new Vector(
+                tx * cos - ty * sin,
+                tx * sin + ty * cos);
+        }
+
+        internal static Vector EvaluateNormal(double semiMajor, double semiMinor, double rotation, double t)
+        {
+            // Inward normal: perpendicular to tangent, pointing toward center of curvature.
+            // In local coords: N(t) = (-b*cos(t), -a*sin(t))
+            var nx = -semiMinor * System.Math.Cos(t);
+            var ny = -semiMajor * System.Math.Sin(t);
+
+            var cos = System.Math.Cos(rotation);
+            var sin = System.Math.Sin(rotation);
+
+            return new Vector(
+                nx * cos - ny * sin,
+                nx * sin + ny * cos);
+        }
+
+        internal static Vector IntersectNormals(Vector p1, Vector n1, Vector p2, Vector n2)
+        {
+            // Solve: p1 + s*n1 = p2 + t*n2
+            var det = n1.X * (-n2.Y) - (-n2.X) * n1.Y;
+            if (System.Math.Abs(det) < 1e-10)
+                return Vector.Invalid;
+
+            var dx = p2.X - p1.X;
+            var dy = p2.Y - p1.Y;
+            var s = (dx * (-n2.Y) - dy * (-n2.X)) / det;
+
+            return new Vector(p1.X + s * n1.X, p1.Y + s * n1.Y);
+        }
+
+        public static List<Entity> Convert(Vector center, double semiMajor, double semiMinor,
+            double rotation, double startParam, double endParam, double tolerance = 0.001)
+        {
+            if (tolerance <= 0)
+                throw new ArgumentOutOfRangeException(nameof(tolerance), "Tolerance must be positive.");
+            if (semiMajor <= 0 || semiMinor <= 0)
+                throw new ArgumentOutOfRangeException("Semi-axis lengths must be positive.");
+
+            if (endParam <= startParam)
+                endParam += Angle.TwoPI;
+
+            // True circle — emit a single arc (or two for full circle)
+            if (System.Math.Abs(semiMajor - semiMinor) < Tolerance.Epsilon)
+                return ConvertCircle(center, semiMajor, rotation, startParam, endParam);
+
+            var splits = GetInitialSplits(startParam, endParam);
+
+            var entities = new List<Entity>();
+            for (var i = 0; i < splits.Count - 1; i++)
+                FitSegment(center, semiMajor, semiMinor, rotation,
+                    splits[i], splits[i + 1], tolerance, entities, 0);
+
+            return entities;
+        }
+
+        private static List<Entity> ConvertCircle(Vector center, double radius,
+            double rotation, double startParam, double endParam)
+        {
+            var sweep = endParam - startParam;
+            var isFull = System.Math.Abs(sweep - Angle.TwoPI) < 0.01;
+
+            if (isFull)
+            {
+                var startAngle1 = Angle.NormalizeRad(startParam + rotation);
+                var midAngle = Angle.NormalizeRad(startParam + System.Math.PI + rotation);
+                var endAngle2 = startAngle1;
+
+                return new List<Entity>
+                {
+                    new Arc(center, radius, startAngle1, midAngle, false),
+                    new Arc(center, radius, midAngle, endAngle2, false)
+                };
+            }
+
+            var sa = Angle.NormalizeRad(startParam + rotation);
+            var ea = Angle.NormalizeRad(endParam + rotation);
+            return new List<Entity> { new Arc(center, radius, sa, ea, false) };
+        }
+
+        private static List<double> GetInitialSplits(double startParam, double endParam)
+        {
+            var splits = new List<double> { startParam };
+
+            var firstQuadrant = System.Math.Ceiling(startParam / (System.Math.PI / 2)) * (System.Math.PI / 2);
+            for (var q = firstQuadrant; q < endParam; q += System.Math.PI / 2)
+            {
+                if (q > startParam + 1e-10 && q < endParam - 1e-10)
+                    splits.Add(q);
+            }
+
+            splits.Add(endParam);
+            return splits;
+        }
+
+        private static void FitSegment(Vector center, double semiMajor, double semiMinor,
+            double rotation, double t0, double t1, double tolerance, List<Entity> results, int depth)
+        {
+            var p0 = EvaluatePoint(semiMajor, semiMinor, rotation, center, t0);
+            var p1 = EvaluatePoint(semiMajor, semiMinor, rotation, center, t1);
+
+            if (p0.DistanceTo(p1) < 1e-10)
+                return;
+
+            var n0 = EvaluateNormal(semiMajor, semiMinor, rotation, t0);
+            var n1 = EvaluateNormal(semiMajor, semiMinor, rotation, t1);
+
+            var arcCenter = IntersectNormals(p0, n0, p1, n1);
+
+            if (!arcCenter.IsValid() || depth >= MaxSubdivisionDepth)
+            {
+                results.Add(new Line(p0, p1));
+                return;
+            }
+
+            var radius = p0.DistanceTo(arcCenter);
+            var maxDev = MeasureDeviation(center, semiMajor, semiMinor, rotation,
+                t0, t1, arcCenter, radius);
+
+            if (maxDev <= tolerance)
+            {
+                results.Add(CreateArc(arcCenter, radius, center, semiMajor, semiMinor, rotation, t0, t1));
+            }
+            else
+            {
+                var tMid = (t0 + t1) / 2.0;
+                FitSegment(center, semiMajor, semiMinor, rotation, t0, tMid, tolerance, results, depth + 1);
+                FitSegment(center, semiMajor, semiMinor, rotation, tMid, t1, tolerance, results, depth + 1);
+            }
+        }
+
+        private static double MeasureDeviation(Vector center, double semiMajor, double semiMinor,
+            double rotation, double t0, double t1, Vector arcCenter, double radius)
+        {
+            var maxDev = 0.0;
+            for (var i = 1; i <= DeviationSamples; i++)
+            {
+                var t = t0 + (t1 - t0) * i / DeviationSamples;
+                var p = EvaluatePoint(semiMajor, semiMinor, rotation, center, t);
+                var dist = p.DistanceTo(arcCenter);
+                var dev = System.Math.Abs(dist - radius);
+                if (dev > maxDev) maxDev = dev;
+            }
+            return maxDev;
+        }
+
+        private static Arc CreateArc(Vector arcCenter, double radius,
+            Vector ellipseCenter, double semiMajor, double semiMinor, double rotation,
+            double t0, double t1)
+        {
+            var p0 = EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, t0);
+            var p1 = EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, t1);
+
+            var startAngle = System.Math.Atan2(p0.Y - arcCenter.Y, p0.X - arcCenter.X);
+            var endAngle = System.Math.Atan2(p1.Y - arcCenter.Y, p1.X - arcCenter.X);
+
+            var pMid = EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, (t0 + t1) / 2);
+            var points = new List<Vector> { p0, pMid, p1 };
+            var isReversed = SumSignedAngles(arcCenter, points) < 0;
+
+            if (startAngle < 0) startAngle += Angle.TwoPI;
+            if (endAngle < 0) endAngle += Angle.TwoPI;
+
+            return new Arc(arcCenter, radius, startAngle, endAngle, isReversed);
+        }
+
+        private static double SumSignedAngles(Vector center, List<Vector> points)
+        {
+            var total = 0.0;
+            for (var i = 0; i < points.Count - 1; i++)
+            {
+                var a1 = System.Math.Atan2(points[i].Y - center.Y, points[i].X - center.X);
+                var a2 = System.Math.Atan2(points[i + 1].Y - center.Y, points[i + 1].X - center.X);
+                var da = a2 - a1;
+                while (da > System.Math.PI) da -= Angle.TwoPI;
+                while (da < -System.Math.PI) da += Angle.TwoPI;
+                total += da;
+            }
+            return total;
+        }
+    }
+}

OpenNest.Core/Geometry/GeometryOptimizer.cs

@@ -76,6 +76,9 @@ namespace OpenNest.Geometry
             if (line1 == line2)
                 return false;
 
+            if (line1.Layer?.Name != line2.Layer?.Name)
+                return false;
+
             if (!line1.IsCollinearTo(line2))
                 return false;
 
@@ -113,9 +116,9 @@ namespace OpenNest.Geometry
             var b = b1 < b2 ? b1 : b2;
 
             if (!line1.IsVertical() && line1.Slope() < 0)
-                lineOut = new Line(new Vector(l, t), new Vector(r, b));
+                lineOut = new Line(new Vector(l, t), new Vector(r, b)) { Layer = line1.Layer, Color = line1.Color };
             else
-                lineOut = new Line(new Vector(l, b), new Vector(r, t));
+                lineOut = new Line(new Vector(l, b), new Vector(r, t)) { Layer = line1.Layer, Color = line1.Color };
 
             return true;
         }
@@ -127,6 +130,9 @@ namespace OpenNest.Geometry
             if (arc1 == arc2)
                 return false;
 
+            if (arc1.Layer?.Name != arc2.Layer?.Name)
+                return false;
+
             if (arc1.Center != arc2.Center)
                 return false;
 
@@ -161,7 +167,7 @@ namespace OpenNest.Geometry
             if (startAngle < 0) startAngle += Angle.TwoPI;
             if (endAngle < 0) endAngle += Angle.TwoPI;
 
-            arcOut = new Arc(arc1.Center, arc1.Radius, startAngle, endAngle);
+            arcOut = new Arc(arc1.Center, arc1.Radius, startAngle, endAngle) { Layer = arc1.Layer, Color = arc1.Color };
 
             return true;
         }

OpenNest.Core/Geometry/GeometrySimplifier.cs

@@ -0,0 +1,703 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Math;
+
+namespace OpenNest.Geometry;
+
+public class ArcCandidate
+{
+    public int ShapeIndex { get; set; }
+    public int StartIndex { get; set; }
+    public int EndIndex { get; set; }
+    public int LineCount => EndIndex - StartIndex + 1;
+    public Arc FittedArc { get; set; }
+    public double MaxDeviation { get; set; }
+    public Box BoundingBox { get; set; }
+    public bool IsSelected { get; set; } = true;
+    /// <summary>First point of the original line segments this candidate covers.</summary>
+    public Vector FirstPoint { get; set; }
+    /// <summary>Last point of the original line segments this candidate covers.</summary>
+    public Vector LastPoint { get; set; }
+}
+
+/// <summary>
+/// A mirror axis defined by a point on the axis and a unit direction vector.
+/// </summary>
+public class MirrorAxisResult
+{
+    public static readonly MirrorAxisResult None = new(Vector.Invalid, Vector.Invalid, 0);
+
+    public Vector Point { get; }
+    public Vector Direction { get; }
+    public double Score { get; }
+    public bool IsValid => Point.IsValid();
+
+    public MirrorAxisResult(Vector point, Vector direction, double score)
+    {
+        Point = point;
+        Direction = direction;
+        Score = score;
+    }
+
+    /// <summary>Reflects a point across this axis.</summary>
+    public Vector Reflect(Vector p)
+    {
+        var dx = p.X - Point.X;
+        var dy = p.Y - Point.Y;
+        var dot = dx * Direction.X + dy * Direction.Y;
+        return new Vector(
+            p.X - 2 * (dx - dot * Direction.X),
+            p.Y - 2 * (dy - dot * Direction.Y));
+    }
+}
+
+public class GeometrySimplifier
+{
+    public double Tolerance { get; set; } = 0.004;
+    public int MinLines { get; set; } = 3;
+
+    public List<ArcCandidate> Analyze(Shape shape)
+    {
+        var candidates = new List<ArcCandidate>();
+        var entities = shape.Entities;
+        var i = 0;
+
+        while (i < entities.Count)
+        {
+            if (entities[i] is not Line and not Arc)
+            {
+                i++;
+                continue;
+            }
+
+            var runStart = i;
+            var layerName = entities[i].Layer?.Name;
+            var lineCount = 0;
+            while (i < entities.Count && (entities[i] is Line || entities[i] is Arc) && entities[i].Layer?.Name == layerName)
+            {
+                if (entities[i] is Line) lineCount++;
+                i++;
+            }
+            var runEnd = i - 1;
+
+            if (lineCount >= MinLines)
+                FindCandidatesInRun(entities, runStart, runEnd, candidates);
+        }
+
+        return candidates;
+    }
+
+    public Shape Apply(Shape shape, List<ArcCandidate> candidates)
+    {
+        var selected = candidates
+            .Where(c => c.IsSelected)
+            .OrderBy(c => c.StartIndex)
+            .ToList();
+
+        var newEntities = new List<Entity>();
+        var i = 0;
+
+        foreach (var candidate in selected)
+        {
+            while (i < candidate.StartIndex)
+            {
+                newEntities.Add(shape.Entities[i]);
+                i++;
+            }
+
+            newEntities.Add(candidate.FittedArc);
+            i = candidate.EndIndex + 1;
+        }
+
+        while (i < shape.Entities.Count)
+        {
+            newEntities.Add(shape.Entities[i]);
+            i++;
+        }
+
+        var result = new Shape();
+        result.Entities.AddRange(newEntities);
+        return result;
+    }
+
+    /// <summary>
+    /// Detects the mirror axis of a shape by testing candidate axes through the
+    /// centroid. Uses PCA to find principal directions, then also tests horizontal
+    /// and vertical. Works for shapes rotated at any angle.
+    /// </summary>
+    public static MirrorAxisResult DetectMirrorAxis(Shape shape)
+    {
+        var midpoints = new List<Vector>();
+        foreach (var e in shape.Entities)
+            midpoints.Add(e.BoundingBox.Center);
+
+        if (midpoints.Count < 4) return MirrorAxisResult.None;
+
+        // Centroid
+        var cx = 0.0;
+        var cy = 0.0;
+        foreach (var p in midpoints) { cx += p.X; cy += p.Y; }
+        cx /= midpoints.Count;
+        cy /= midpoints.Count;
+        var centroid = new Vector(cx, cy);
+
+        // Covariance matrix for PCA
+        var cxx = 0.0;
+        var cxy = 0.0;
+        var cyy = 0.0;
+        foreach (var p in midpoints)
+        {
+            var dx = p.X - cx;
+            var dy = p.Y - cy;
+            cxx += dx * dx;
+            cxy += dx * dy;
+            cyy += dy * dy;
+        }
+
+        // Eigenvectors of 2x2 symmetric matrix via analytic formula
+        var trace = cxx + cyy;
+        var det = cxx * cyy - cxy * cxy;
+        var disc = System.Math.Sqrt(System.Math.Max(0, trace * trace / 4 - det));
+        var lambda1 = trace / 2 + disc;
+        var lambda2 = trace / 2 - disc;
+
+        var candidates = new List<Vector>();
+
+        // PCA eigenvectors (major and minor axes)
+        if (System.Math.Abs(cxy) > 1e-10)
+        {
+            candidates.Add(Normalize(new Vector(lambda1 - cyy, cxy)));
+            candidates.Add(Normalize(new Vector(lambda2 - cyy, cxy)));
+        }
+        else
+        {
+            candidates.Add(new Vector(1, 0));
+            candidates.Add(new Vector(0, 1));
+        }
+
+        // Also always test pure horizontal and vertical
+        candidates.Add(new Vector(1, 0));
+        candidates.Add(new Vector(0, 1));
+
+        // Score each candidate axis
+        var bestResult = MirrorAxisResult.None;
+        foreach (var dir in candidates)
+        {
+            var score = MirrorMatchScore(midpoints, centroid, dir);
+            if (score > bestResult.Score)
+                bestResult = new MirrorAxisResult(centroid, dir, score);
+        }
+
+        return bestResult.Score >= 0.8 ? bestResult : MirrorAxisResult.None;
+    }
+
+    private static Vector Normalize(Vector v)
+    {
+        var len = System.Math.Sqrt(v.X * v.X + v.Y * v.Y);
+        return len < 1e-10 ? new Vector(1, 0) : new Vector(v.X / len, v.Y / len);
+    }
+
+    private static double MirrorMatchScore(List<Vector> points, Vector axisPoint, Vector axisDir)
+    {
+        var matchTol = 0.1;
+        var matched = 0;
+
+        for (var i = 0; i < points.Count; i++)
+        {
+            var p = points[i];
+
+            // Distance from point to axis
+            var dx = p.X - axisPoint.X;
+            var dy = p.Y - axisPoint.Y;
+            var dot = dx * axisDir.X + dy * axisDir.Y;
+            var perpX = dx - dot * axisDir.X;
+            var perpY = dy - dot * axisDir.Y;
+            var dist = System.Math.Sqrt(perpX * perpX + perpY * perpY);
+
+            // Points on the axis count as matched
+            if (dist < matchTol)
+            {
+                matched++;
+                continue;
+            }
+
+            // Reflect across axis and look for partner
+            var mx = p.X - 2 * perpX;
+            var my = p.Y - 2 * perpY;
+
+            for (var j = 0; j < points.Count; j++)
+            {
+                if (i == j) continue;
+                var d = System.Math.Sqrt((points[j].X - mx) * (points[j].X - mx) +
+                                         (points[j].Y - my) * (points[j].Y - my));
+                if (d < matchTol)
+                {
+                    matched++;
+                    break;
+                }
+            }
+        }
+
+        return (double)matched / points.Count;
+    }
+
+    /// <summary>
+    /// Pairs candidates across a mirror axis and forces each pair to use
+    /// the same arc (mirrored). The candidate with more lines or lower
+    /// deviation is kept as the source.
+    /// </summary>
+    public void Symmetrize(List<ArcCandidate> candidates, MirrorAxisResult axis)
+    {
+        if (!axis.IsValid || candidates.Count < 2) return;
+
+        var paired = new HashSet<int>();
+
+        for (var i = 0; i < candidates.Count; i++)
+        {
+            if (paired.Contains(i)) continue;
+
+            var ci = candidates[i];
+            var ciCenter = ci.BoundingBox.Center;
+
+            // Distance from candidate center to axis
+            var dx = ciCenter.X - axis.Point.X;
+            var dy = ciCenter.Y - axis.Point.Y;
+            var dot = dx * axis.Direction.X + dy * axis.Direction.Y;
+            var perpDist = System.Math.Sqrt((dx - dot * axis.Direction.X) * (dx - dot * axis.Direction.X) +
+                                            (dy - dot * axis.Direction.Y) * (dy - dot * axis.Direction.Y));
+            if (perpDist < 0.1) continue; // on the axis
+
+            var mirrorCenter = axis.Reflect(ciCenter);
+
+            var bestJ = -1;
+            var bestDist = double.MaxValue;
+            for (var j = i + 1; j < candidates.Count; j++)
+            {
+                if (paired.Contains(j)) continue;
+                var d = mirrorCenter.DistanceTo(candidates[j].BoundingBox.Center);
+                if (d < bestDist)
+                {
+                    bestDist = d;
+                    bestJ = j;
+                }
+            }
+
+            var matchTol = System.Math.Max(ci.BoundingBox.Width, ci.BoundingBox.Length) * 0.5;
+            if (bestJ < 0 || bestDist > matchTol) continue;
+
+            paired.Add(i);
+            paired.Add(bestJ);
+
+            var cj = candidates[bestJ];
+            var sourceIdx = i;
+            var targetIdx = bestJ;
+            if (cj.LineCount > ci.LineCount || (cj.LineCount == ci.LineCount && cj.MaxDeviation < ci.MaxDeviation))
+            {
+                sourceIdx = bestJ;
+                targetIdx = i;
+            }
+
+            var source = candidates[sourceIdx];
+            var target = candidates[targetIdx];
+            var mirrored = MirrorArc(source.FittedArc, axis);
+
+            // Only apply the mirrored arc if its endpoints are close enough to the
+            // target's actual boundary points. Otherwise the mirror introduces gaps.
+            var mirroredStart = mirrored.StartPoint();
+            var mirroredEnd = mirrored.EndPoint();
+            var startDist = mirroredStart.DistanceTo(target.FirstPoint);
+            var endDist = mirroredEnd.DistanceTo(target.LastPoint);
+
+            if (startDist <= Tolerance && endDist <= Tolerance)
+            {
+                target.FittedArc = mirrored;
+                target.MaxDeviation = source.MaxDeviation;
+            }
+        }
+    }
+
+    private static Arc MirrorArc(Arc arc, MirrorAxisResult axis)
+    {
+        var mirrorCenter = axis.Reflect(arc.Center);
+
+        // Reflect start and end points, then compute new angles
+        var sp = arc.StartPoint();
+        var ep = arc.EndPoint();
+        var mirrorSp = axis.Reflect(sp);
+        var mirrorEp = axis.Reflect(ep);
+
+        // Mirroring reverses winding — swap start/end to preserve arc direction
+        var mirrorStart = System.Math.Atan2(mirrorEp.Y - mirrorCenter.Y, mirrorEp.X - mirrorCenter.X);
+        var mirrorEnd = System.Math.Atan2(mirrorSp.Y - mirrorCenter.Y, mirrorSp.X - mirrorCenter.X);
+
+        // Normalize to [0, 2pi)
+        if (mirrorStart < 0) mirrorStart += Angle.TwoPI;
+        if (mirrorEnd < 0) mirrorEnd += Angle.TwoPI;
+
+        var result = new Arc(mirrorCenter, arc.Radius, mirrorStart, mirrorEnd, arc.IsReversed);
+        result.Layer = arc.Layer;
+        result.Color = arc.Color;
+        return result;
+    }
+
+    private void FindCandidatesInRun(List<Entity> entities, int runStart, int runEnd, List<ArcCandidate> candidates)
+    {
+        var j = runStart;
+        var chainedTangent = Vector.Invalid;
+
+        while (j <= runEnd - MinLines + 1)
+        {
+            var result = TryFitArcAt(entities, j, runEnd, chainedTangent);
+            if (result == null)
+            {
+                j++;
+                chainedTangent = Vector.Invalid;
+                continue;
+            }
+
+            chainedTangent = ComputeEndTangent(result.Center, result.Points);
+            candidates.Add(new ArcCandidate
+            {
+                StartIndex = j,
+                EndIndex = result.EndIndex,
+                FittedArc = CreateArc(result.Center, result.Radius, result.Points, entities[j]),
+                MaxDeviation = result.Deviation,
+                BoundingBox = result.Points.GetBoundingBox(),
+                FirstPoint = result.Points[0],
+                LastPoint = result.Points[^1],
+            });
+
+            j = result.EndIndex + 1;
+        }
+    }
+
+    private record ArcFitResult(Vector Center, double Radius, double Deviation, List<Vector> Points, int EndIndex);
+
+    private ArcFitResult TryFitArcAt(List<Entity> entities, int start, int runEnd, Vector chainedTangent)
+    {
+        var k = start + MinLines - 1;
+        if (k > runEnd) return null;
+
+        var points = CollectPoints(entities, start, k);
+        if (points.Count < 3) return null;
+
+        var startTangent = chainedTangent.IsValid()
+            ? chainedTangent
+            : new Vector(points[1].X - points[0].X, points[1].Y - points[0].Y);
+
+        var (center, radius, dev) = TryFit(points, startTangent);
+        if (!center.IsValid()) return null;
+
+        // Extend the arc as far as possible
+        while (k + 1 <= runEnd)
+        {
+            var extPoints = CollectPoints(entities, start, k + 1);
+            var (nc, nr, nd) = extPoints.Count >= 3 ? TryFit(extPoints, startTangent) : (Vector.Invalid, 0, 0d);
+            if (!nc.IsValid()) break;
+
+            k++;
+            center = nc;
+            radius = nr;
+            dev = nd;
+            points = extPoints;
+        }
+
+        // Reject arcs that subtend a tiny angle — these are nearly-straight lines
+        // that happen to fit a huge circle. Applied after extension so that many small
+        // segments can accumulate enough sweep to qualify.
+        var sweep = System.Math.Abs(SumSignedAngles(center, points));
+        if (sweep < Angle.ToRadians(5))
+            return null;
+
+        return new ArcFitResult(center, radius, dev, points, k);
+    }
+
+    private (Vector center, double radius, double deviation) TryFit(List<Vector> points, Vector startTangent)
+    {
+        var (center, radius, dev) = FitWithStartTangent(points, startTangent);
+        if (!center.IsValid() || dev > Tolerance)
+            (center, radius, dev) = FitMirrorAxis(points);
+        if (!center.IsValid() || dev > Tolerance)
+            return (Vector.Invalid, 0, 0);
+
+        // Check that the arc doesn't bulge away from the original line segments
+        var isReversed = SumSignedAngles(center, points) < 0;
+        var arcDev = MaxArcToSegmentDeviation(points, center, radius, isReversed);
+        if (arcDev > Tolerance)
+            return (Vector.Invalid, 0, 0);
+
+        return (center, radius, System.Math.Max(dev, arcDev));
+    }
+
+    /// <summary>
+    /// Fits a circular arc constrained to be tangent to the given direction at the
+    /// first point. The center lies at the intersection of the normal at P1 (perpendicular
+    /// to the tangent) and the perpendicular bisector of the chord P1->Pn, guaranteeing
+    /// the arc passes through both endpoints and departs P1 in the given direction.
+    /// </summary>
+    private static (Vector center, double radius, double deviation) FitWithStartTangent(
+        List<Vector> points, Vector tangent)
+    {
+        if (points.Count < 3)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var p1 = points[0];
+        var pn = points[^1];
+
+        var mx = (p1.X + pn.X) / 2;
+        var my = (p1.Y + pn.Y) / 2;
+        var dx = pn.X - p1.X;
+        var dy = pn.Y - p1.Y;
+        var chordLen = System.Math.Sqrt(dx * dx + dy * dy);
+        if (chordLen < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var bx = -dy / chordLen;
+        var by = dx / chordLen;
+
+        var tLen = System.Math.Sqrt(tangent.X * tangent.X + tangent.Y * tangent.Y);
+        if (tLen < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var nx = -tangent.Y / tLen;
+        var ny = tangent.X / tLen;
+
+        var det = nx * by - ny * bx;
+        if (System.Math.Abs(det) < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var t = ((mx - p1.X) * by - (my - p1.Y) * bx) / det;
+
+        var cx = p1.X + t * nx;
+        var cy = p1.Y + t * ny;
+        var radius = System.Math.Sqrt((cx - p1.X) * (cx - p1.X) + (cy - p1.Y) * (cy - p1.Y));
+
+        if (radius < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        return (new Vector(cx, cy), radius, MaxRadialDeviation(points, cx, cy, radius));
+    }
+
+    /// <summary>
+    /// Computes the tangent direction at the last point of a fitted arc,
+    /// used to chain tangent continuity to the next arc.
+    /// </summary>
+    private static Vector ComputeEndTangent(Vector center, List<Vector> points)
+    {
+        var lastPt = points[^1];
+        var totalAngle = SumSignedAngles(center, points);
+
+        var rx = lastPt.X - center.X;
+        var ry = lastPt.Y - center.Y;
+
+        if (totalAngle >= 0)
+            return new Vector(-ry, rx);
+        else
+            return new Vector(ry, -rx);
+    }
+
+    /// <summary>
+    /// Fits a circular arc using the mirror axis approach. The center is constrained
+    /// to the perpendicular bisector of the chord (P1->Pn), guaranteeing the arc
+    /// passes exactly through both endpoints. Golden section search optimizes position.
+    /// </summary>
+    private (Vector center, double radius, double deviation) FitMirrorAxis(List<Vector> points)
+    {
+        if (points.Count < 3)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var p1 = points[0];
+        var pn = points[^1];
+        var mx = (p1.X + pn.X) / 2;
+        var my = (p1.Y + pn.Y) / 2;
+        var dx = pn.X - p1.X;
+        var dy = pn.Y - p1.Y;
+        var chordLen = System.Math.Sqrt(dx * dx + dy * dy);
+        if (chordLen < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var halfChord = chordLen / 2;
+        var nx = -dy / chordLen;
+        var ny = dx / chordLen;
+
+        var maxSagitta = 0.0;
+        for (var i = 1; i < points.Count - 1; i++)
+        {
+            var proj = (points[i].X - mx) * nx + (points[i].Y - my) * ny;
+            if (System.Math.Abs(proj) > System.Math.Abs(maxSagitta))
+                maxSagitta = proj;
+        }
+        if (System.Math.Abs(maxSagitta) < 1e-10)
+            return (Vector.Invalid, 0, double.MaxValue);
+
+        var dInit = (maxSagitta * maxSagitta - halfChord * halfChord) / (2 * maxSagitta);
+        var range = System.Math.Max(System.Math.Abs(dInit) * 2, halfChord);
+
+        var dOpt = GoldenSectionMin(dInit - range, dInit + range,
+            d => MaxRadialDeviation(points, mx + d * nx, my + d * ny,
+                System.Math.Sqrt(halfChord * halfChord + d * d)));
+
+        var center = new Vector(mx + dOpt * nx, my + dOpt * ny);
+        var radius = System.Math.Sqrt(halfChord * halfChord + dOpt * dOpt);
+        return (center, radius, MaxRadialDeviation(points, center.X, center.Y, radius));
+    }
+
+    private static double GoldenSectionMin(double low, double high, Func<double, double> eval)
+    {
+        var phi = (System.Math.Sqrt(5) - 1) / 2;
+        for (var iter = 0; iter < 30; iter++)
+        {
+            var d1 = high - phi * (high - low);
+            var d2 = low + phi * (high - low);
+            if (eval(d1) < eval(d2))
+                high = d2;
+            else
+                low = d1;
+            if (high - low < 1e-6)
+                break;
+        }
+        return (low + high) / 2;
+    }
+
+    private static List<Vector> CollectPoints(List<Entity> entities, int start, int end)
+    {
+        var points = new List<Vector>();
+
+        for (var i = start; i <= end; i++)
+        {
+            switch (entities[i])
+            {
+                case Line line:
+                    if (i == start)
+                        points.Add(line.StartPoint);
+                    points.Add(line.EndPoint);
+                    break;
+
+                case Arc arc:
+                    if (i == start)
+                        points.Add(arc.StartPoint());
+                    var segments = System.Math.Max(2, arc.SegmentsForTolerance(0.1));
+                    var arcPoints = arc.ToPoints(segments);
+                    for (var j = 1; j < arcPoints.Count; j++)
+                        points.Add(arcPoints[j]);
+                    break;
+            }
+        }
+
+        return points;
+    }
+
+    private static Arc CreateArc(Vector center, double radius, List<Vector> points, Entity sourceEntity)
+    {
+        var firstPoint = points[0];
+        var lastPoint = points[^1];
+
+        var startAngle = System.Math.Atan2(firstPoint.Y - center.Y, firstPoint.X - center.X);
+        var endAngle = System.Math.Atan2(lastPoint.Y - center.Y, lastPoint.X - center.X);
+        var isReversed = SumSignedAngles(center, points) < 0;
+
+        // Normalize to [0, 2pi)
+        if (startAngle < 0) startAngle += Angle.TwoPI;
+        if (endAngle < 0) endAngle += Angle.TwoPI;
+
+        var arc = new Arc(center, radius, startAngle, endAngle, isReversed);
+        arc.Layer = sourceEntity.Layer;
+        arc.Color = sourceEntity.Color;
+        return arc;
+    }
+
+    /// <summary>
+    /// Sums signed angular change traversing consecutive points around a center.
+    /// Positive = CCW, negative = CW.
+    /// </summary>
+    private static double SumSignedAngles(Vector center, List<Vector> points)
+    {
+        var total = 0.0;
+        for (var i = 0; i < points.Count - 1; i++)
+        {
+            var a1 = System.Math.Atan2(points[i].Y - center.Y, points[i].X - center.X);
+            var a2 = System.Math.Atan2(points[i + 1].Y - center.Y, points[i + 1].X - center.X);
+            var da = a2 - a1;
+            while (da > System.Math.PI) da -= Angle.TwoPI;
+            while (da < -System.Math.PI) da += Angle.TwoPI;
+            total += da;
+        }
+        return total;
+    }
+
+    /// <summary>
+    /// Max deviation of intermediate points (excluding endpoints) from a circle.
+    /// </summary>
+    private static double MaxRadialDeviation(List<Vector> points, double cx, double cy, double radius)
+    {
+        var maxDev = 0.0;
+        for (var i = 1; i < points.Count - 1; i++)
+        {
+            var px = points[i].X - cx;
+            var py = points[i].Y - cy;
+            var dist = System.Math.Sqrt(px * px + py * py);
+            var dev = System.Math.Abs(dist - radius);
+            if (dev > maxDev) maxDev = dev;
+        }
+        return maxDev;
+    }
+
+    /// <summary>
+    /// Measures the maximum distance from sampled points along the fitted arc
+    /// back to the original line segments. This catches cases where points lie
+    /// on a large circle but the arc bulges far from the original straight geometry.
+    /// </summary>
+    private static double MaxArcToSegmentDeviation(List<Vector> points, Vector center, double radius, bool isReversed)
+    {
+        var startAngle = System.Math.Atan2(points[0].Y - center.Y, points[0].X - center.X);
+        var endAngle = System.Math.Atan2(points[^1].Y - center.Y, points[^1].X - center.X);
+
+        var sweep = endAngle - startAngle;
+        if (isReversed)
+        {
+            if (sweep > 0) sweep -= Angle.TwoPI;
+        }
+        else
+        {
+            if (sweep < 0) sweep += Angle.TwoPI;
+        }
+
+        var sampleCount = System.Math.Max(10, (int)(System.Math.Abs(sweep) * radius * 10));
+        sampleCount = System.Math.Min(sampleCount, 100);
+
+        var maxDev = 0.0;
+        for (var i = 1; i < sampleCount; i++)
+        {
+            var t = (double)i / sampleCount;
+            var angle = startAngle + sweep * t;
+            var px = center.X + radius * System.Math.Cos(angle);
+            var py = center.Y + radius * System.Math.Sin(angle);
+            var arcPt = new Vector(px, py);
+
+            var minDist = double.MaxValue;
+            for (var j = 0; j < points.Count - 1; j++)
+            {
+                var dist = DistanceToSegment(arcPt, points[j], points[j + 1]);
+                if (dist < minDist) minDist = dist;
+            }
+            if (minDist > maxDev) maxDev = minDist;
+        }
+        return maxDev;
+    }
+
+    private static double DistanceToSegment(Vector p, Vector a, Vector b)
+    {
+        var dx = b.X - a.X;
+        var dy = b.Y - a.Y;
+        var lenSq = dx * dx + dy * dy;
+        if (lenSq < 1e-20)
+            return System.Math.Sqrt((p.X - a.X) * (p.X - a.X) + (p.Y - a.Y) * (p.Y - a.Y));
+
+        var t = ((p.X - a.X) * dx + (p.Y - a.Y) * dy) / lenSq;
+        t = System.Math.Max(0, System.Math.Min(1, t));
+        var projX = a.X + t * dx;
+        var projY = a.Y + t * dy;
+        return System.Math.Sqrt((p.X - projX) * (p.X - projX) + (p.Y - projY) * (p.Y - projY));
+    }
+}

OpenNest.Core/Geometry/SplineConverter.cs

@@ -0,0 +1,247 @@
+using OpenNest.Math;
+using System;
+using System.Collections.Generic;
+
+namespace OpenNest.Geometry
+{
+    public static class SplineConverter
+    {
+        private const int MinPointsForArc = 3;
+
+        public static List<Entity> Convert(List<Vector> points, bool isClosed, double tolerance = 0.001)
+        {
+            if (points == null || points.Count < 2)
+                return new List<Entity>();
+
+            var entities = new List<Entity>();
+            var i = 0;
+            var chainedTangent = Vector.Invalid;
+
+            while (i < points.Count - 1)
+            {
+                var result = TryFitArc(points, i, chainedTangent, tolerance);
+                if (result != null)
+                {
+                    entities.Add(result.Arc);
+                    chainedTangent = result.EndTangent;
+                    i = result.EndIndex;
+                }
+                else
+                {
+                    entities.Add(new Line(points[i], points[i + 1]));
+                    chainedTangent = Vector.Invalid;
+                    i++;
+                }
+            }
+
+            return entities;
+        }
+
+        private static ArcFitResult TryFitArc(List<Vector> points, int start,
+            Vector chainedTangent, double tolerance)
+        {
+            var minEnd = start + MinPointsForArc - 1;
+            if (minEnd >= points.Count)
+                return null;
+
+            var hasTangent = chainedTangent.IsValid();
+
+            var subPoints = points.GetRange(start, MinPointsForArc);
+            var (center, radius, dev) = hasTangent
+                ? FitWithStartTangent(subPoints, chainedTangent)
+                : FitCircumscribed(subPoints);
+
+            if (!center.IsValid() || dev > tolerance)
+                return null;
+
+            var endIdx = minEnd;
+            while (endIdx + 1 < points.Count)
+            {
+                var extPoints = points.GetRange(start, endIdx + 1 - start + 1);
+                var (nc, nr, nd) = hasTangent
+                    ? FitWithStartTangent(extPoints, chainedTangent)
+                    : FitCircumscribed(extPoints);
+
+                if (!nc.IsValid() || nd > tolerance)
+                    break;
+
+                endIdx++;
+                center = nc;
+                radius = nr;
+                dev = nd;
+            }
+
+            var finalPoints = points.GetRange(start, endIdx - start + 1);
+            var sweep = System.Math.Abs(SumSignedAngles(center, finalPoints));
+            if (sweep < Angle.ToRadians(5))
+                return null;
+
+            var arc = CreateArc(center, radius, finalPoints);
+            var endTangent = ComputeEndTangent(center, finalPoints);
+
+            return new ArcFitResult(arc, endTangent, endIdx);
+        }
+
+        private static (Vector center, double radius, double deviation) FitCircumscribed(
+            List<Vector> points)
+        {
+            if (points.Count < 3)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var p0 = points[0];
+            var pMid = points[points.Count / 2];
+            var pEnd = points[^1];
+
+            // Find circumcenter by intersecting perpendicular bisectors of two chords
+            var (center, radius) = Circumcenter(p0, pMid, pEnd);
+            if (!center.IsValid())
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            return (center, radius, MaxRadialDeviation(points, center.X, center.Y, radius));
+        }
+
+        private static (Vector center, double radius) Circumcenter(Vector a, Vector b, Vector c)
+        {
+            // Perpendicular bisector of chord a-b
+            var m1x = (a.X + b.X) / 2;
+            var m1y = (a.Y + b.Y) / 2;
+            var d1x = -(b.Y - a.Y);
+            var d1y = b.X - a.X;
+
+            // Perpendicular bisector of chord b-c
+            var m2x = (b.X + c.X) / 2;
+            var m2y = (b.Y + c.Y) / 2;
+            var d2x = -(c.Y - b.Y);
+            var d2y = c.X - b.X;
+
+            var det = d1x * d2y - d1y * d2x;
+            if (System.Math.Abs(det) < 1e-10)
+                return (Vector.Invalid, 0);
+
+            var t = ((m2x - m1x) * d2y - (m2y - m1y) * d2x) / det;
+
+            var cx = m1x + t * d1x;
+            var cy = m1y + t * d1y;
+            var radius = System.Math.Sqrt((cx - a.X) * (cx - a.X) + (cy - a.Y) * (cy - a.Y));
+
+            if (radius < 1e-10)
+                return (Vector.Invalid, 0);
+
+            return (new Vector(cx, cy), radius);
+        }
+
+        private static (Vector center, double radius, double deviation) FitWithStartTangent(
+            List<Vector> points, Vector tangent)
+        {
+            if (points.Count < 3)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var p1 = points[0];
+            var pn = points[^1];
+
+            var mx = (p1.X + pn.X) / 2;
+            var my = (p1.Y + pn.Y) / 2;
+            var dx = pn.X - p1.X;
+            var dy = pn.Y - p1.Y;
+            var chordLen = System.Math.Sqrt(dx * dx + dy * dy);
+            if (chordLen < 1e-10)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var bx = -dy / chordLen;
+            var by = dx / chordLen;
+
+            var tLen = System.Math.Sqrt(tangent.X * tangent.X + tangent.Y * tangent.Y);
+            if (tLen < 1e-10)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var nx = -tangent.Y / tLen;
+            var ny = tangent.X / tLen;
+
+            var det = nx * by - ny * bx;
+            if (System.Math.Abs(det) < 1e-10)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            var s = ((mx - p1.X) * by - (my - p1.Y) * bx) / det;
+
+            var cx = p1.X + s * nx;
+            var cy = p1.Y + s * ny;
+            var radius = System.Math.Sqrt((cx - p1.X) * (cx - p1.X) + (cy - p1.Y) * (cy - p1.Y));
+
+            if (radius < 1e-10)
+                return (Vector.Invalid, 0, double.MaxValue);
+
+            return (new Vector(cx, cy), radius, MaxRadialDeviation(points, cx, cy, radius));
+        }
+
+        private static double MaxRadialDeviation(List<Vector> points, double cx, double cy, double radius)
+        {
+            var maxDev = 0.0;
+            for (var i = 1; i < points.Count - 1; i++)
+            {
+                var px = points[i].X - cx;
+                var py = points[i].Y - cy;
+                var dist = System.Math.Sqrt(px * px + py * py);
+                var dev = System.Math.Abs(dist - radius);
+                if (dev > maxDev) maxDev = dev;
+            }
+            return maxDev;
+        }
+
+        private static double SumSignedAngles(Vector center, List<Vector> points)
+        {
+            var total = 0.0;
+            for (var i = 0; i < points.Count - 1; i++)
+            {
+                var a1 = System.Math.Atan2(points[i].Y - center.Y, points[i].X - center.X);
+                var a2 = System.Math.Atan2(points[i + 1].Y - center.Y, points[i + 1].X - center.X);
+                var da = a2 - a1;
+                while (da > System.Math.PI) da -= Angle.TwoPI;
+                while (da < -System.Math.PI) da += Angle.TwoPI;
+                total += da;
+            }
+            return total;
+        }
+
+        private static Vector ComputeEndTangent(Vector center, List<Vector> points)
+        {
+            var lastPt = points[^1];
+            var totalAngle = SumSignedAngles(center, points);
+
+            var rx = lastPt.X - center.X;
+            var ry = lastPt.Y - center.Y;
+
+            return totalAngle >= 0
+                ? new Vector(-ry, rx)
+                : new Vector(ry, -rx);
+        }
+
+        private static Arc CreateArc(Vector center, double radius, List<Vector> points)
+        {
+            var firstPoint = points[0];
+            var lastPoint = points[^1];
+
+            var startAngle = System.Math.Atan2(firstPoint.Y - center.Y, firstPoint.X - center.X);
+            var endAngle = System.Math.Atan2(lastPoint.Y - center.Y, lastPoint.X - center.X);
+            var isReversed = SumSignedAngles(center, points) < 0;
+
+            if (startAngle < 0) startAngle += Angle.TwoPI;
+            if (endAngle < 0) endAngle += Angle.TwoPI;
+
+            return new Arc(center, radius, startAngle, endAngle, isReversed);
+        }
+
+        private sealed class ArcFitResult
+        {
+            public Arc Arc { get; }
+            public Vector EndTangent { get; }
+            public int EndIndex { get; }
+
+            public ArcFitResult(Arc arc, Vector endTangent, int endIndex)
+            {
+                Arc = arc;
+                EndTangent = endTangent;
+                EndIndex = endIndex;
+            }
+        }
+    }
+}

OpenNest.Core/OpenNest.Core.csproj

@@ -4,6 +4,9 @@
     <RootNamespace>OpenNest</RootNamespace>
     <AssemblyName>OpenNest.Core</AssemblyName>
   </PropertyGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="OpenNest.Tests" />
+  </ItemGroup>
   <ItemGroup>
     <PackageReference Include="Clipper2" Version="2.0.0" />
     <PackageReference Include="System.Drawing.Common" Version="8.0.10" />

OpenNest.Core/Part.cs

@@ -1,6 +1,7 @@
 using OpenNest.CNC;
 using OpenNest.Converters;
 using OpenNest.Geometry;
+using OpenNest.Math;
 using System.Collections.Generic;
 using System.Linq;
 
@@ -173,7 +174,53 @@ namespace OpenNest
             perimeter1.Offset(Location);
             perimeter2.Offset(part.Location);
 
-            return perimeter1.Intersects(perimeter2, out pts);
+            if (!perimeter1.Intersects(perimeter2, out var rawPts))
+                return false;
+
+            // Exclude intersection points that coincide with vertices of BOTH
+            // perimeters — these are touch points (shared corners/endpoints),
+            // not actual crossings where one shape enters the other's interior.
+            var verts1 = CollectVertices(perimeter1);
+            var verts2 = CollectVertices(perimeter2);
+
+            foreach (var pt in rawPts)
+            {
+                if (IsNearAnyVertex(pt, verts1) && IsNearAnyVertex(pt, verts2))
+                    continue;
+                pts.Add(pt);
+            }
+
+            return pts.Count > 0;
+        }
+
+        private static List<Vector> CollectVertices(Geometry.Shape shape)
+        {
+            var verts = new List<Vector>();
+            foreach (var entity in shape.Entities)
+            {
+                switch (entity)
+                {
+                    case Geometry.Line line:
+                        verts.Add(line.StartPoint);
+                        verts.Add(line.EndPoint);
+                        break;
+                    case Geometry.Arc arc:
+                        verts.Add(arc.StartPoint());
+                        verts.Add(arc.EndPoint());
+                        break;
+                }
+            }
+            return verts;
+        }
+
+        private static bool IsNearAnyVertex(Vector pt, List<Vector> vertices)
+        {
+            foreach (var v in vertices)
+            {
+                if (pt.X.IsEqualTo(v.X) && pt.Y.IsEqualTo(v.Y))
+                    return true;
+            }
+            return false;
         }
 
         public double Left

OpenNest.Core/Plate.cs

@@ -601,10 +601,24 @@ namespace OpenNest
             for (var i = 0; i < realParts.Count; i++)
             {
                 var part1 = realParts[i];
+                var b1 = part1.BoundingBox;
 
                 for (var j = i + 1; j < realParts.Count; j++)
                 {
                     var part2 = realParts[j];
+                    var b2 = part2.BoundingBox;
+
+                    // Skip pairs whose bounding boxes don't meaningfully overlap.
+                    // Floating-point rounding can produce sub-epsilon overlaps for
+                    // parts that are merely edge-touching, so require the overlap
+                    // region to exceed Epsilon in both dimensions.
+                    var overlapX = System.Math.Min(b1.Right, b2.Right)
+                                 - System.Math.Max(b1.Left, b2.Left);
+                    var overlapY = System.Math.Min(b1.Top, b2.Top)
+                                 - System.Math.Max(b1.Bottom, b2.Bottom);
+
+                    if (overlapX <= Math.Tolerance.Epsilon || overlapY <= Math.Tolerance.Epsilon)
+                        continue;
 
                     if (part1.Intersects(part2, out var pts2))
                         pts.AddRange(pts2);

OpenNest.Engine/Fill/FillExtents.cs

@@ -47,13 +47,21 @@ namespace OpenNest.Engine.Fill
 
             var adjusted = AdjustColumn(pair.Value, column, token);
 
+            // The iterative pair adjustment can shift parts enough to cause
+            // genuine overlap. Fall back to the unadjusted column when this happens.
+            if (HasOverlappingParts(adjusted))
+            {
+                Debug.WriteLine("[FillExtents] Adjusted column has overlaps, using unadjusted");
+                adjusted = column;
+            }
+
             NestEngineBase.ReportProgress(progress, new ProgressReport
             {
                 Phase = NestPhase.Extents,
                 PlateNumber = plateNumber,
                 Parts = adjusted,
                 WorkArea = workArea,
-                Description = $"Extents: adjusted column {adjusted.Count} parts",
+                Description = $"Extents: column {adjusted.Count} parts",
             });
 
             var result = RepeatColumns(adjusted, token);
@@ -386,5 +394,31 @@ namespace OpenNest.Engine.Fill
                    part.BoundingBox.Left >= workArea.Left - Tolerance.Epsilon &&
                    part.BoundingBox.Bottom >= workArea.Bottom - Tolerance.Epsilon;
         }
+
+        private static bool HasOverlappingParts(List<Part> parts)
+        {
+            for (var i = 0; i < parts.Count; i++)
+            {
+                var b1 = parts[i].BoundingBox;
+
+                for (var j = i + 1; j < parts.Count; j++)
+                {
+                    var b2 = parts[j].BoundingBox;
+
+                    var overlapX = System.Math.Min(b1.Right, b2.Right)
+                                 - System.Math.Max(b1.Left, b2.Left);
+                    var overlapY = System.Math.Min(b1.Top, b2.Top)
+                                 - System.Math.Max(b1.Bottom, b2.Bottom);
+
+                    if (overlapX <= Tolerance.Epsilon || overlapY <= Tolerance.Epsilon)
+                        continue;
+
+                    if (parts[i].Intersects(parts[j], out _))
+                        return true;
+                }
+            }
+
+            return false;
+        }
     }
 }

OpenNest.Engine/Fill/StripeFiller.cs

@@ -158,6 +158,15 @@ public class StripeFiller
         if (gridParts.Count == 0)
             return null;
 
+        // Reject results where bounding boxes overlap — the angle convergence
+        // can produce slightly off-axis rotations where FillLinear's copy
+        // distance calculation doesn't fully account for the rotated geometry.
+        if (HasOverlappingParts(gridParts))
+        {
+            Debug.WriteLine($"[StripeFiller] Rejected grid: overlapping bounding boxes detected");
+            return null;
+        }
+
         var allParts = new List<Part>(gridParts);
 
         var remnantParts = FillRemnant(gridParts, primaryAxis);
@@ -470,4 +479,34 @@ public class StripeFiller
     {
         return axis == NestDirection.Horizontal ? box.Width : box.Length;
     }
+
+    /// <summary>
+    /// Checks if any pair of parts geometrically overlap. Uses bounding box
+    /// pre-filtering for performance, then falls back to shape intersection.
+    /// </summary>
+    private static bool HasOverlappingParts(List<Part> parts)
+    {
+        for (var i = 0; i < parts.Count; i++)
+        {
+            var b1 = parts[i].BoundingBox;
+
+            for (var j = i + 1; j < parts.Count; j++)
+            {
+                var b2 = parts[j].BoundingBox;
+
+                var overlapX = System.Math.Min(b1.Right, b2.Right)
+                             - System.Math.Max(b1.Left, b2.Left);
+                var overlapY = System.Math.Min(b1.Top, b2.Top)
+                             - System.Math.Max(b1.Bottom, b2.Bottom);
+
+                if (overlapX <= Tolerance.Epsilon || overlapY <= Tolerance.Epsilon)
+                    continue;
+
+                if (parts[i].Intersects(parts[j], out _))
+                    return true;
+            }
+        }
+
+        return false;
+    }
 }

OpenNest.Engine/Strategies/FillStrategyRegistry.cs

@@ -22,6 +22,17 @@ namespace OpenNest.Engine.Strategies
         public static IReadOnlyList<IFillStrategy> Strategies =>
             sorted ??= FilterStrategies();
 
+        /// <summary>
+        /// Returns all registered strategies regardless of enabled/disabled state.
+        /// </summary>
+        public static IReadOnlyList<IFillStrategy> AllStrategies =>
+            strategies.OrderBy(s => s.Order).ToList();
+
+        /// <summary>
+        /// Returns the names of all permanently disabled strategies.
+        /// </summary>
+        public static IReadOnlyCollection<string> DisabledNames => disabled;
+
         private static List<IFillStrategy> FilterStrategies()
         {
             var source = enabledFilter != null

OpenNest.IO/Bending/SolidWorksBendDetector.cs

@@ -63,9 +63,72 @@ namespace OpenNest.IO.Bending
                     bends.Add(bend);
             }
 
+            PropagateCollinearBendNotes(bends);
+
             return bends;
         }
 
+        /// <summary>
+        /// For bends without a note (e.g. split by a cutout), copy angle/radius/direction
+        /// from a collinear bend that does have a note.
+        /// </summary>
+        private static void PropagateCollinearBendNotes(List<Bend> bends)
+        {
+            const double angleTolerance = 0.01; // radians
+            const double distanceTolerance = 0.01;
+
+            foreach (var bend in bends)
+            {
+                if (!string.IsNullOrEmpty(bend.NoteText))
+                    continue;
+
+                foreach (var other in bends)
+                {
+                    if (string.IsNullOrEmpty(other.NoteText))
+                        continue;
+
+                    if (!AreCollinear(bend, other, angleTolerance, distanceTolerance))
+                        continue;
+
+                    bend.Direction = other.Direction;
+                    bend.Angle = other.Angle;
+                    bend.Radius = other.Radius;
+                    bend.NoteText = other.NoteText;
+                    break;
+                }
+            }
+        }
+
+        private static bool AreCollinear(Bend a, Bend b, double angleTolerance, double distanceTolerance)
+        {
+            var angleA = a.StartPoint.AngleTo(a.EndPoint);
+            var angleB = b.StartPoint.AngleTo(b.EndPoint);
+
+            // Normalize angle difference to [0, PI) since opposite directions are still collinear
+            var diff = System.Math.Abs(angleA - angleB) % System.Math.PI;
+            if (diff > angleTolerance && System.Math.PI - diff > angleTolerance)
+                return false;
+
+            // Perpendicular distance from midpoint of A to the infinite line through B
+            var midA = new Vector(
+                (a.StartPoint.X + a.EndPoint.X) / 2.0,
+                (a.StartPoint.Y + a.EndPoint.Y) / 2.0);
+
+            var dx = b.EndPoint.X - b.StartPoint.X;
+            var dy = b.EndPoint.Y - b.StartPoint.Y;
+            var len = System.Math.Sqrt(dx * dx + dy * dy);
+
+            if (len < 1e-9)
+                return false;
+
+            // 2D cross product gives signed perpendicular distance * length
+            var vx = midA.X - b.StartPoint.X;
+            var vy = midA.Y - b.StartPoint.Y;
+            var perp = System.Math.Abs(vx * dy - vy * dx) / len;
+
+            return perp <= distanceTolerance;
+        }
+
         private List<ACadSharp.Entities.Line> FindBendLines(CadDocument document)
         {
             return document.Entities

OpenNest.IO/DxfImporter.cs

@@ -24,9 +24,10 @@ namespace OpenNest.IO
 
             foreach (var entity in doc.Entities)
             {
-                // Skip bend line entities — they are converted to Bend objects
-                // separately via bend detection, not cut geometry.
-                if (IsBendLayer(entity.Layer?.Name))
+                // Skip bend/etch entities — bends are converted to Bend objects
+                // separately via bend detection, and etch marks are generated from
+                // bends during DXF export. Neither should be treated as cut geometry.
+                if (IsNonCutLayer(entity.Layer?.Name))
                     continue;
 
                 switch (entity)
@@ -44,7 +45,11 @@ namespace OpenNest.IO
                         break;
 
                     case ACadSharp.Entities.Spline spline:
-                        lines.AddRange(spline.ToOpenNest());
+                        foreach (var e in spline.ToOpenNest(SplinePrecision))
+                        {
+                            if (e is Line l) lines.Add(l);
+                            else if (e is Arc a) arcs.Add(a);
+                        }
                         break;
 
                     case ACadSharp.Entities.LwPolyline lwPolyline:
@@ -56,7 +61,11 @@ namespace OpenNest.IO
                         break;
 
                     case ACadSharp.Entities.Ellipse ellipse:
-                        lines.AddRange(ellipse.ToOpenNest(SplinePrecision));
+                        foreach (var e in ellipse.ToOpenNest())
+                        {
+                            if (e is Line l) lines.Add(l);
+                            else if (e is Arc a) arcs.Add(a);
+                        }
                         break;
                 }
             }
@@ -137,9 +146,10 @@ namespace OpenNest.IO
             return success;
         }
 
-        private static bool IsBendLayer(string layerName)
+        private static bool IsNonCutLayer(string layerName)
         {
-            return string.Equals(layerName, "BEND", System.StringComparison.OrdinalIgnoreCase);
+            return string.Equals(layerName, "BEND", System.StringComparison.OrdinalIgnoreCase)
+                || string.Equals(layerName, "ETCH", System.StringComparison.OrdinalIgnoreCase);
         }
     }
 }

OpenNest.IO/Extensions.cs

@@ -1,6 +1,7 @@
 using ACadSharp.Entities;
 using CSMath;
 using OpenNest.Geometry;
+using System;
 using System.Collections.Generic;
 using System.Drawing;
 using System.Linq;
@@ -56,42 +57,46 @@ namespace OpenNest.IO
             return result;
         }
 
-        public static List<Geometry.Line> ToOpenNest(this Spline spline)
+        public static List<Geometry.Entity> ToOpenNest(this Spline spline, int precision)
         {
-            var lines = new List<Geometry.Line>();
-            var pts = spline.ControlPoints;
-
-            if (pts.Count == 0)
-                return lines;
-
             var layer = spline.Layer.ToOpenNest();
             var color = spline.ResolveColor();
             var lineTypeName = spline.ResolveLineTypeName();
-            var lastPoint = pts[0].ToOpenNest();
 
-            for (var i = 1; i < pts.Count; i++)
+            // Evaluate actual points on the spline curve (not control points)
+            List<XYZ> curvePoints;
+            try
             {
-                var nextPoint = pts[i].ToOpenNest();
-
-                lines.Add(new Geometry.Line(lastPoint, nextPoint)
-                {
-                    Layer = layer,
-                    Color = color,
-                    LineTypeName = lineTypeName
-                });
-
-                lastPoint = nextPoint;
+                curvePoints = spline.PolygonalVertexes(precision > 0 ? precision : 200);
+            }
+            catch (Exception ex)
+            {
+                System.Diagnostics.Debug.WriteLine($"Spline curve evaluation failed: {ex.Message}");
+                curvePoints = null;
             }
 
-            if (spline.IsClosed)
-                lines.Add(new Geometry.Line(lastPoint, pts[0].ToOpenNest())
-                {
-                    Layer = layer,
-                    Color = color,
-                    LineTypeName = lineTypeName
-                });
+            if (curvePoints == null || curvePoints.Count < 2)
+            {
+                // Fallback: use control points if evaluation fails
+                curvePoints = new List<XYZ>(spline.ControlPoints);
+                if (curvePoints.Count < 2)
+                    return new List<Geometry.Entity>();
+            }
 
-            return lines;
+            var points = new List<Vector>(curvePoints.Count);
+            foreach (var pt in curvePoints)
+                points.Add(pt.ToOpenNest());
+
+            var entities = SplineConverter.Convert(points, spline.IsClosed, tolerance: 0.001);
+
+            foreach (var entity in entities)
+            {
+                entity.Layer = layer;
+                entity.Color = color;
+                entity.LineTypeName = lineTypeName;
+            }
+
+            return entities;
         }
 
         public static List<Geometry.Line> ToOpenNest(this Polyline polyline)
@@ -172,69 +177,32 @@ namespace OpenNest.IO
             return lines;
         }
 
-        public static List<Geometry.Line> ToOpenNest(this ACadSharp.Entities.Ellipse ellipse, int precision = 200)
+        public static List<Geometry.Entity> ToOpenNest(this ACadSharp.Entities.Ellipse ellipse, double tolerance = 0.001)
         {
-            var lines = new List<Geometry.Line>();
-
             var center = new Vector(ellipse.Center.X, ellipse.Center.Y);
             var majorAxis = new Vector(ellipse.MajorAxisEndPoint.X, ellipse.MajorAxisEndPoint.Y);
-            var majorLength = System.Math.Sqrt(majorAxis.X * majorAxis.X + majorAxis.Y * majorAxis.Y);
-            var minorLength = majorLength * ellipse.RadiusRatio;
+            var semiMajor = System.Math.Sqrt(majorAxis.X * majorAxis.X + majorAxis.Y * majorAxis.Y);
+            var semiMinor = semiMajor * ellipse.RadiusRatio;
             var rotation = System.Math.Atan2(majorAxis.Y, majorAxis.X);
 
             var startParam = ellipse.StartParameter;
             var endParam = ellipse.EndParameter;
 
-            if (endParam <= startParam)
-                endParam += System.Math.PI * 2.0;
-
-            var step = (endParam - startParam) / precision;
-
-            var points = new List<Vector>();
-
-            for (var i = 0; i <= precision; i++)
-            {
-                var t = startParam + step * i;
-                var x = majorLength * System.Math.Cos(t);
-                var y = minorLength * System.Math.Sin(t);
-
-                // Rotate by the major axis angle and translate to center
-                var cos = System.Math.Cos(rotation);
-                var sin = System.Math.Sin(rotation);
-                var px = center.X + x * cos - y * sin;
-                var py = center.Y + x * sin + y * cos;
-
-                points.Add(new Vector(px, py));
-            }
-
             var layer = ellipse.Layer.ToOpenNest();
             var color = ellipse.ResolveColor();
             var lineTypeName = ellipse.ResolveLineTypeName();
 
-            for (var i = 0; i < points.Count - 1; i++)
+            var entities = EllipseConverter.Convert(center, semiMajor, semiMinor, rotation,
+                startParam, endParam, tolerance);
+
+            foreach (var entity in entities)
             {
-                lines.Add(new Geometry.Line(points[i], points[i + 1])
-                {
-                    Layer = layer,
-                    Color = color,
-                    LineTypeName = lineTypeName
-                });
+                entity.Layer = layer;
+                entity.Color = color;
+                entity.LineTypeName = lineTypeName;
             }
 
-            // Close the ellipse if it's a full ellipse
-            if (lines.Count >= 2)
-            {
-                var first = lines.First();
-                var last = lines.Last();
-                lines.Add(new Geometry.Line(last.EndPoint, first.StartPoint)
-                {
-                    Layer = layer,
-                    Color = color,
-                    LineTypeName = lineTypeName
-                });
-            }
-
-            return lines;
+            return entities;
         }
 
         public static Geometry.Layer ToOpenNest(this ACadSharp.Tables.Layer layer)

OpenNest.Posts.Cincinnati/CincinnatiPartSubprogramWriter.cs

@@ -29,12 +29,12 @@ public sealed class CincinnatiPartSubprogramWriter
     public void Write(TextWriter w, Program normalizedProgram, string drawingName,
         int subNumber, string cutLibrary, string etchLibrary, double sheetDiagonal)
     {
-        var allFeatures = SplitFeatures(normalizedProgram.Codes);
+        var allFeatures = FeatureUtils.SplitByRapids(normalizedProgram.Codes);
         if (allFeatures.Count == 0)
             return;
 
         // Classify and order: etch features first, then cut features
-        var ordered = OrderFeatures(allFeatures);
+        var ordered = FeatureUtils.ClassifyAndOrder(allFeatures);
 
         w.WriteLine("(*****************************************************)");
         w.WriteLine($":{subNumber}");
@@ -46,7 +46,7 @@ public sealed class CincinnatiPartSubprogramWriter
             var featureNumber = i == 0
                 ? _config.FeatureLineNumberStart
                 : 1000 + i + 1;
-            var cutDistance = ComputeCutDistance(codes);
+            var cutDistance = FeatureUtils.ComputeCutDistance(codes);
 
             var ctx = new FeatureContext
             {
@@ -70,81 +70,43 @@ public sealed class CincinnatiPartSubprogramWriter
         w.WriteLine($"M99 (END OF {drawingName})");
     }
 
-    internal static List<(List<ICode> codes, bool isEtch)> OrderFeatures(List<List<ICode>> features)
-    {
-        var result = new List<(List<ICode>, bool)>();
-        var etch = new List<List<ICode>>();
-        var cut = new List<List<ICode>>();
-
-        foreach (var f in features)
-        {
-            if (CincinnatiSheetWriter.IsFeatureEtch(f))
-                etch.Add(f);
-            else
-                cut.Add(f);
-        }
-
-        foreach (var f in etch)
-            result.Add((f, true));
-        foreach (var f in cut)
-            result.Add((f, false));
-
-        return result;
-    }
-
     /// <summary>
     /// Creates a sub-program key for matching parts to their sub-programs.
     /// </summary>
     internal static (int drawingId, long rotationKey) SubprogramKey(Part part) =>
         (part.BaseDrawing.Id, (long)System.Math.Round(part.Rotation * 1e6));
 
-    internal static List<List<ICode>> SplitFeatures(List<ICode> codes)
+    /// <summary>
+    /// Scans all plates and builds a mapping of unique part geometries to sub-program numbers,
+    /// along with their normalized programs for writing.
+    /// </summary>
+    internal static (Dictionary<(int, long), int> mapping, List<(int subNum, string name, Program program)> entries)
+        BuildRegistry(IEnumerable<Plate> plates, int startNumber)
     {
-        var features = new List<List<ICode>>();
-        List<ICode> current = null;
+        var mapping = new Dictionary<(int, long), int>();
+        var entries = new List<(int, string, Program)>();
+        var nextSubNum = startNumber;
 
-        foreach (var code in codes)
+        foreach (var plate in plates)
         {
-            if (code is RapidMove)
+            foreach (var part in plate.Parts)
             {
-                if (current != null)
-                    features.Add(current);
-                current = new List<ICode> { code };
-            }
-            else
-            {
-                current ??= new List<ICode>();
-                current.Add(code);
+                if (part.BaseDrawing.IsCutOff) continue;
+                var key = SubprogramKey(part);
+                if (!mapping.ContainsKey(key))
+                {
+                    var subNum = nextSubNum++;
+                    mapping[key] = subNum;
+
+                    var pgm = part.Program.Clone() as Program;
+                    var bbox = pgm.BoundingBox();
+                    pgm.Offset(-bbox.Location.X, -bbox.Location.Y);
+
+                    entries.Add((subNum, part.BaseDrawing.Name, pgm));
+                }
             }
         }
 
-        if (current != null && current.Count > 0)
-            features.Add(current);
-
-        return features;
-    }
-
-    internal static double ComputeCutDistance(List<ICode> codes)
-    {
-        var distance = 0.0;
-        var currentPos = Vector.Zero;
-
-        foreach (var code in codes)
-        {
-            if (code is RapidMove rapid)
-                currentPos = rapid.EndPoint;
-            else if (code is LinearMove linear)
-            {
-                distance += currentPos.DistanceTo(linear.EndPoint);
-                currentPos = linear.EndPoint;
-            }
-            else if (code is ArcMove arc)
-            {
-                distance += currentPos.DistanceTo(arc.EndPoint);
-                currentPos = arc.EndPoint;
-            }
-        }
-
-        return distance;
+        return (mapping, entries);
     }
 }

OpenNest.Posts.Cincinnati/CincinnatiPostProcessor.cs

@@ -84,32 +84,7 @@ namespace OpenNest.Posts.Cincinnati
             List<(int subNum, string name, Program program)> subprogramEntries = null;
 
             if (Config.UsePartSubprograms)
-            {
-                partSubprograms = new Dictionary<(int, long), int>();
-                subprogramEntries = new List<(int, string, Program)>();
-                var nextSubNum = Config.PartSubprogramStart;
-
-                foreach (var plate in plates)
-                {
-                    foreach (var part in plate.Parts)
-                    {
-                        if (part.BaseDrawing.IsCutOff) continue;
-                        var key = CincinnatiPartSubprogramWriter.SubprogramKey(part);
-                        if (!partSubprograms.ContainsKey(key))
-                        {
-                            var subNum = nextSubNum++;
-                            partSubprograms[key] = subNum;
-
-                            // Create normalized program at origin
-                            var pgm = part.Program.Clone() as Program;
-                            var bbox = pgm.BoundingBox();
-                            pgm.Offset(-bbox.Location.X, -bbox.Location.Y);
-
-                            subprogramEntries.Add((subNum, part.BaseDrawing.Name, pgm));
-                        }
-                    }
-                }
-            }
+                (partSubprograms, subprogramEntries) = CincinnatiPartSubprogramWriter.BuildRegistry(plates, Config.PartSubprogramStart);
 
             // 5. Create writers
             var preamble = new CincinnatiPreambleWriter(Config);

OpenNest.Posts.Cincinnati/CincinnatiSheetWriter.cs

@@ -4,7 +4,6 @@ using System.IO;
 using System.Linq;
 using System.Text;
 using OpenNest.CNC;
-using OpenNest.Geometry;
 
 namespace OpenNest.Posts.Cincinnati;
 
@@ -128,7 +127,7 @@ public sealed class CincinnatiSheetWriter
             else
             {
                 // Inline features for cutoffs or parts without sub-programs
-                var features = SplitAndOrderFeatures(part);
+                var features = FeatureUtils.SplitAndClassify(part);
                 for (var f = 0; f < features.Count; f++)
                 {
                     var (codes, isEtch) = features[f];
@@ -137,7 +136,7 @@ public sealed class CincinnatiSheetWriter
                         : 1000 + featureIndex + 1;
 
                     var isLastFeature = isLastPart && f == features.Count - 1;
-                    var cutDistance = ComputeCutDistance(codes);
+                    var cutDistance = FeatureUtils.ComputeCutDistance(codes);
 
                     var ctx = new FeatureContext
                     {
@@ -205,7 +204,7 @@ public sealed class CincinnatiSheetWriter
         var features = new List<(Part part, List<ICode> codes, bool isEtch)>();
         foreach (var part in allParts)
         {
-            var partFeatures = SplitAndOrderFeatures(part);
+            var partFeatures = FeatureUtils.SplitAndClassify(part);
             foreach (var (codes, isEtch) in partFeatures)
                 features.Add((part, codes, isEtch));
         }
@@ -224,7 +223,7 @@ public sealed class CincinnatiSheetWriter
                 ? _config.FeatureLineNumberStart
                 : 1000 + i + 1;
 
-            var cutDistance = ComputeCutDistance(codes);
+            var cutDistance = FeatureUtils.ComputeCutDistance(codes);
 
             var ctx = new FeatureContext
             {
@@ -246,91 +245,4 @@ public sealed class CincinnatiSheetWriter
         }
     }
 
-    /// <summary>
-    /// Splits a part's program into features (by rapids), classifies each as etch or cut,
-    /// and orders etch features before cut features.
-    /// </summary>
-    public static List<(List<ICode> codes, bool isEtch)> SplitAndOrderFeatures(Part part)
-    {
-        var etchFeatures = new List<List<ICode>>();
-        var cutFeatures = new List<List<ICode>>();
-        List<ICode> current = null;
-
-        foreach (var code in part.Program.Codes)
-        {
-            if (code is RapidMove)
-            {
-                if (current != null)
-                    ClassifyAndAdd(current, etchFeatures, cutFeatures);
-                current = new List<ICode> { code };
-            }
-            else
-            {
-                current ??= new List<ICode>();
-                current.Add(code);
-            }
-        }
-
-        if (current != null && current.Count > 0)
-            ClassifyAndAdd(current, etchFeatures, cutFeatures);
-
-        // Etch features first, then cut features
-        var result = new List<(List<ICode>, bool)>();
-        foreach (var f in etchFeatures)
-            result.Add((f, true));
-        foreach (var f in cutFeatures)
-            result.Add((f, false));
-
-        return result;
-    }
-
-    private static void ClassifyAndAdd(List<ICode> codes,
-        List<List<ICode>> etchFeatures, List<List<ICode>> cutFeatures)
-    {
-        if (IsFeatureEtch(codes))
-            etchFeatures.Add(codes);
-        else
-            cutFeatures.Add(codes);
-    }
-
-    /// <summary>
-    /// A feature is etch if any non-rapid move has LayerType.Scribe.
-    /// </summary>
-    public static bool IsFeatureEtch(List<ICode> codes)
-    {
-        foreach (var code in codes)
-        {
-            if (code is LinearMove linear && linear.Layer == LayerType.Scribe)
-                return true;
-            if (code is ArcMove arc && arc.Layer == LayerType.Scribe)
-                return true;
-        }
-        return false;
-    }
-
-    private static double ComputeCutDistance(List<ICode> codes)
-    {
-        var distance = 0.0;
-        var currentPos = Vector.Zero;
-
-        foreach (var code in codes)
-        {
-            if (code is RapidMove rapid)
-            {
-                currentPos = rapid.EndPoint;
-            }
-            else if (code is LinearMove linear)
-            {
-                distance += currentPos.DistanceTo(linear.EndPoint);
-                currentPos = linear.EndPoint;
-            }
-            else if (code is ArcMove arc)
-            {
-                distance += currentPos.DistanceTo(arc.EndPoint);
-                currentPos = arc.EndPoint;
-            }
-        }
-
-        return distance;
-    }
 }

OpenNest.Posts.Cincinnati/FeatureUtils.cs

@@ -0,0 +1,115 @@
+using System.Collections.Generic;
+using OpenNest.CNC;
+using OpenNest.Geometry;
+
+namespace OpenNest.Posts.Cincinnati;
+
+/// <summary>
+/// Shared utilities for splitting CNC programs into features and classifying them.
+/// </summary>
+public static class FeatureUtils
+{
+    /// <summary>
+    /// Splits a flat list of codes into feature groups, breaking on rapid moves.
+    /// Each feature starts with a rapid move followed by cutting/etching moves.
+    /// </summary>
+    public static List<List<ICode>> SplitByRapids(List<ICode> codes)
+    {
+        var features = new List<List<ICode>>();
+        List<ICode> current = null;
+
+        foreach (var code in codes)
+        {
+            if (code is RapidMove)
+            {
+                if (current != null)
+                    features.Add(current);
+                current = new List<ICode> { code };
+            }
+            else
+            {
+                current ??= new List<ICode>();
+                current.Add(code);
+            }
+        }
+
+        if (current != null && current.Count > 0)
+            features.Add(current);
+
+        return features;
+    }
+
+    /// <summary>
+    /// Classifies features as etch or cut and orders etch features before cut features.
+    /// </summary>
+    public static List<(List<ICode> codes, bool isEtch)> ClassifyAndOrder(List<List<ICode>> features)
+    {
+        var result = new List<(List<ICode>, bool)>();
+        var etch = new List<List<ICode>>();
+        var cut = new List<List<ICode>>();
+
+        foreach (var f in features)
+        {
+            if (IsEtch(f))
+                etch.Add(f);
+            else
+                cut.Add(f);
+        }
+
+        foreach (var f in etch)
+            result.Add((f, true));
+        foreach (var f in cut)
+            result.Add((f, false));
+
+        return result;
+    }
+
+    /// <summary>
+    /// Splits a part's program into features by rapids, classifies each as etch or cut,
+    /// and orders etch features before cut features.
+    /// </summary>
+    public static List<(List<ICode> codes, bool isEtch)> SplitAndClassify(Part part) =>
+        ClassifyAndOrder(SplitByRapids(part.Program.Codes));
+
+    /// <summary>
+    /// Returns true if any non-rapid move in the feature has LayerType.Scribe.
+    /// </summary>
+    public static bool IsEtch(List<ICode> codes)
+    {
+        foreach (var code in codes)
+        {
+            if (code is LinearMove linear && linear.Layer == LayerType.Scribe)
+                return true;
+            if (code is ArcMove arc && arc.Layer == LayerType.Scribe)
+                return true;
+        }
+        return false;
+    }
+
+    /// <summary>
+    /// Computes the total cut distance of a feature by summing segment lengths.
+    /// </summary>
+    public static double ComputeCutDistance(List<ICode> codes)
+    {
+        var distance = 0.0;
+        var currentPos = Vector.Zero;
+
+        foreach (var code in codes)
+        {
+            if (code is RapidMove rapid)
+                currentPos = rapid.EndPoint;
+            else if (code is LinearMove linear)
+            {
+                distance += currentPos.DistanceTo(linear.EndPoint);
+                currentPos = linear.EndPoint;
+            }
+            else if (code is ArcMove arc)
+            {
+                distance += currentPos.DistanceTo(arc.EndPoint);
+                currentPos = arc.EndPoint;
+            }
+        }
+
+        return distance;
+    }
+}

OpenNest.Tests/Bending/SolidWorksBendDetectorTests.cs

@@ -29,6 +29,76 @@ public class SolidWorksBendDetectorTests
         Assert.Empty(bends);
     }
 
+    [Fact]
+    public void EllipseConverter_ProducesArcsDirectly()
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "Bending", "TestData", "4526 A14 PT11 Test.dxf");
+        Assert.True(File.Exists(path), $"Test DXF not found: {path}");
+
+        var importer = new OpenNest.IO.DxfImporter { SplinePrecision = 200 };
+        var result = importer.Import(path);
+
+        // EllipseConverter now produces arcs directly during import,
+        // so the imported entities should contain Arc instances from the ellipses
+        var arcCount = result.Entities.Count(e => e is OpenNest.Geometry.Arc);
+        Assert.True(arcCount > 0, "Expected arcs from ellipse conversion");
+
+        // The GeometrySimplifier should find few or no line runs to simplify,
+        // because ellipses are already converted to arcs at import time
+        var shape = new OpenNest.Geometry.Shape();
+        shape.Entities.AddRange(result.Entities);
+
+        var simplifier = new OpenNest.Geometry.GeometrySimplifier();
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.True(candidates.Count <= 10,
+            $"Expected <=10 simplifier candidates but got {candidates.Count}");
+    }
+
+    [Fact]
+    public void Import_TrimmedEllipse_NoClosingChord()
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "Bending", "TestData", "4526 A14 PT11.dxf");
+        Assert.True(File.Exists(path), $"Test DXF not found: {path}");
+
+        var importer = new OpenNest.IO.DxfImporter();
+        var result = importer.Import(path);
+
+        // The DXF has 2 trimmed ellipses forming an oblong slot.
+        // Trimmed ellipses must not generate a closing chord line.
+        // EllipseConverter now produces arcs instead of line segments,
+        // changing the entity count. Verify arcs are present and no
+        // spurious closing chord exists.
+        var arcCount = result.Entities.Count(e => e is OpenNest.Geometry.Arc);
+        var circleCount = result.Entities.Count(e => e is OpenNest.Geometry.Circle);
+
+        Assert.True(arcCount > 0, "Expected arcs from ellipse conversion");
+        Assert.True(circleCount >= 7, $"Expected at least 7 circles, got {circleCount}");
+        Assert.Equal(115, result.Entities.Count);
+    }
+
+    [Fact]
+    public void DetectBends_SplitBendLine_PropagatesNote()
+    {
+        var path = Path.Combine(AppContext.BaseDirectory, "Bending", "TestData", "4526 A14 PT23.dxf");
+        Assert.True(File.Exists(path), $"Test DXF not found: {path}");
+
+        using var reader = new DxfReader(path);
+        var doc = reader.Read();
+
+        var detector = new SolidWorksBendDetector();
+        var bends = detector.DetectBends(doc);
+
+        Assert.Equal(5, bends.Count);
+        Assert.All(bends, b =>
+        {
+            Assert.NotNull(b.NoteText);
+            Assert.Equal(BendDirection.Up, b.Direction);
+            Assert.Equal(90.0, b.Angle);
+            Assert.Equal(0.125, b.Radius);
+        });
+    }
+
     [Fact]
     public void DetectBends_RealDxf_ParsesNotesCorrectly()
     {

OpenNest.Tests/Cincinnati/CincinnatiSheetWriterTests.cs

@@ -152,7 +152,7 @@ public class CincinnatiSheetWriterTests
             new LinearMove(1, 1) { Layer = LayerType.Scribe }
         };
 
-        Assert.True(CincinnatiSheetWriter.IsFeatureEtch(codes));
+        Assert.True(FeatureUtils.IsEtch(codes));
     }
 
     [Fact]
@@ -165,7 +165,7 @@ public class CincinnatiSheetWriterTests
             new LinearMove(1, 1) { Layer = LayerType.Cut }
         };
 
-        Assert.False(CincinnatiSheetWriter.IsFeatureEtch(codes));
+        Assert.False(FeatureUtils.IsEtch(codes));
     }
 
     [Fact]
@@ -176,7 +176,7 @@ public class CincinnatiSheetWriterTests
             new RapidMove(0, 0)
         };
 
-        Assert.False(CincinnatiSheetWriter.IsFeatureEtch(codes));
+        Assert.False(FeatureUtils.IsEtch(codes));
     }
 
     private static Program CreateSimpleProgram()

OpenNest.Tests/EllipseConverterTests.cs

@@ -0,0 +1,293 @@
+using OpenNest.Geometry;
+using OpenNest.Math;
+using Xunit;
+using System.Linq;
+
+namespace OpenNest.Tests;
+
+public class EllipseConverterTests
+{
+    private const double Tol = 1e-10;
+
+    [Fact]
+    public void EvaluatePoint_AtZero_ReturnsMajorAxisEnd()
+    {
+        var p = EllipseConverter.EvaluatePoint(10, 5, 0, new Vector(0, 0), 0);
+        Assert.InRange(p.X, 10 - Tol, 10 + Tol);
+        Assert.InRange(p.Y, -Tol, Tol);
+    }
+
+    [Fact]
+    public void EvaluatePoint_AtHalfPi_ReturnsMinorAxisEnd()
+    {
+        var p = EllipseConverter.EvaluatePoint(10, 5, 0, new Vector(0, 0), System.Math.PI / 2);
+        Assert.InRange(p.X, -Tol, Tol);
+        Assert.InRange(p.Y, 5 - Tol, 5 + Tol);
+    }
+
+    [Fact]
+    public void EvaluatePoint_WithRotation_RotatesCorrectly()
+    {
+        var p = EllipseConverter.EvaluatePoint(10, 5, System.Math.PI / 2, new Vector(0, 0), 0);
+        Assert.InRange(p.X, -Tol, Tol);
+        Assert.InRange(p.Y, 10 - Tol, 10 + Tol);
+    }
+
+    [Fact]
+    public void EvaluatePoint_WithCenter_TranslatesCorrectly()
+    {
+        var p = EllipseConverter.EvaluatePoint(10, 5, 0, new Vector(100, 200), 0);
+        Assert.InRange(p.X, 110 - Tol, 110 + Tol);
+        Assert.InRange(p.Y, 200 - Tol, 200 + Tol);
+    }
+
+    [Fact]
+    public void EvaluateTangent_AtZero_PointsUp()
+    {
+        var t = EllipseConverter.EvaluateTangent(10, 5, 0, 0);
+        Assert.InRange(t.X, -Tol, Tol);
+        Assert.True(t.Y > 0);
+    }
+
+    [Fact]
+    public void EvaluateNormal_AtZero_PointsInward()
+    {
+        var n = EllipseConverter.EvaluateNormal(10, 5, 0, 0);
+        Assert.True(n.X < 0);
+        Assert.InRange(n.Y, -Tol, Tol);
+    }
+
+    [Fact]
+    public void IntersectNormals_PerpendicularNormals_FindsCenter()
+    {
+        var p1 = new Vector(5, 0);
+        var n1 = new Vector(-1, 0);
+        var p2 = new Vector(0, 5);
+        var n2 = new Vector(0, -1);
+        var center = EllipseConverter.IntersectNormals(p1, n1, p2, n2);
+        Assert.InRange(center.X, -Tol, Tol);
+        Assert.InRange(center.Y, -Tol, Tol);
+    }
+
+    [Fact]
+    public void IntersectNormals_ParallelNormals_ReturnsInvalid()
+    {
+        var p1 = new Vector(0, 0);
+        var n1 = new Vector(1, 0);
+        var p2 = new Vector(0, 5);
+        var n2 = new Vector(1, 0);
+        var center = EllipseConverter.IntersectNormals(p1, n1, p2, n2);
+        Assert.False(center.IsValid());
+    }
+
+    [Fact]
+    public void Convert_Circle_ProducesOneOrTwoArcs()
+    {
+        var result = EllipseConverter.Convert(
+            new Vector(0, 0), semiMajor: 10, semiMinor: 10, rotation: 0,
+            startParam: 0, endParam: Angle.TwoPI, tolerance: 0.001);
+
+        Assert.All(result, e => Assert.IsType<Arc>(e));
+        Assert.InRange(result.Count, 1, 4);
+    }
+
+    [Fact]
+    public void Convert_ModerateEllipse_AllArcsWithinTolerance()
+    {
+        var a = 10.0;
+        var b = 7.0;
+        var tolerance = 0.001;
+        var result = EllipseConverter.Convert(
+            new Vector(0, 0), a, b, rotation: 0,
+            startParam: 0, endParam: Angle.TwoPI, tolerance: tolerance);
+
+        Assert.True(result.Count >= 4, $"Expected at least 4 arcs, got {result.Count}");
+        Assert.All(result, e => Assert.IsType<Arc>(e));
+
+        foreach (var entity in result)
+        {
+            var arc = (Arc)entity;
+            var maxDev = MaxDeviationFromEllipse(arc, new Vector(0, 0), a, b, 0, 50);
+            Assert.True(maxDev <= tolerance,
+                $"Arc at center ({arc.Center.X:F4},{arc.Center.Y:F4}) r={arc.Radius:F4} " +
+                $"deviates {maxDev:F6} from ellipse (tolerance={tolerance})");
+        }
+    }
+
+    [Fact]
+    public void Convert_HighlyEccentricEllipse_ProducesMoreArcs()
+    {
+        var a = 20.0;
+        var b = 3.0;
+        var tolerance = 0.001;
+        var result = EllipseConverter.Convert(
+            new Vector(0, 0), a, b, rotation: 0,
+            startParam: 0, endParam: Angle.TwoPI, tolerance: tolerance);
+
+        Assert.True(result.Count >= 8, $"Expected at least 8 arcs for eccentric ellipse, got {result.Count}");
+        Assert.All(result, e => Assert.IsType<Arc>(e));
+
+        foreach (var entity in result)
+        {
+            var arc = (Arc)entity;
+            var maxDev = MaxDeviationFromEllipse(arc, new Vector(0, 0), a, b, 0, 50);
+            Assert.True(maxDev <= tolerance,
+                $"Deviation {maxDev:F6} exceeds tolerance {tolerance}");
+        }
+    }
+
+    [Fact]
+    public void Convert_PartialEllipse_CoversArcOnly()
+    {
+        var a = 10.0;
+        var b = 5.0;
+        var tolerance = 0.001;
+        var result = EllipseConverter.Convert(
+            new Vector(0, 0), a, b, rotation: 0,
+            startParam: 0, endParam: System.Math.PI / 2, tolerance: tolerance);
+
+        Assert.NotEmpty(result);
+        Assert.All(result, e => Assert.IsType<Arc>(e));
+
+        var firstArc = (Arc)result[0];
+        var sp = firstArc.StartPoint();
+        Assert.InRange(sp.X, a - 0.01, a + 0.01);
+        Assert.InRange(sp.Y, -0.01, 0.01);
+
+        var lastArc = (Arc)result[^1];
+        var ep = lastArc.EndPoint();
+        Assert.InRange(ep.X, -0.01, 0.01);
+        Assert.InRange(ep.Y, b - 0.01, b + 0.01);
+    }
+
+    [Fact]
+    public void Convert_EndpointContinuity_ArcsConnect()
+    {
+        var result = EllipseConverter.Convert(
+            new Vector(5, 10), semiMajor: 15, semiMinor: 8, rotation: 0.5,
+            startParam: 0, endParam: Angle.TwoPI, tolerance: 0.001);
+
+        for (var i = 0; i < result.Count - 1; i++)
+        {
+            var current = (Arc)result[i];
+            var next = (Arc)result[i + 1];
+            var gap = current.EndPoint().DistanceTo(next.StartPoint());
+            Assert.True(gap < 0.001,
+                $"Gap of {gap:F6} between arc {i} and arc {i + 1}");
+        }
+
+        var lastArc = (Arc)result[^1];
+        var firstArc = (Arc)result[0];
+        var closingGap = lastArc.EndPoint().DistanceTo(firstArc.StartPoint());
+        Assert.True(closingGap < 0.001,
+            $"Closing gap of {closingGap:F6}");
+    }
+
+    [Fact]
+    public void Convert_WithRotationAndOffset_ProducesValidArcs()
+    {
+        var center = new Vector(50, -30);
+        var rotation = System.Math.PI / 3;
+        var a = 12.0;
+        var b = 6.0;
+        var tolerance = 0.001;
+
+        var result = EllipseConverter.Convert(center, a, b, rotation,
+            startParam: 0, endParam: Angle.TwoPI, tolerance: tolerance);
+
+        Assert.NotEmpty(result);
+        foreach (var entity in result)
+        {
+            var arc = (Arc)entity;
+            var maxDev = MaxDeviationFromEllipse(arc, center, a, b, rotation, 50);
+            Assert.True(maxDev <= tolerance,
+                $"Deviation {maxDev:F6} exceeds tolerance {tolerance}");
+        }
+    }
+
+    [Fact]
+    public void DxfImporter_EllipseInDxf_ProducesArcsNotLines()
+    {
+        // Create a DXF in memory with an ellipse and verify import produces arcs
+        var doc = new ACadSharp.CadDocument();
+        var ellipse = new ACadSharp.Entities.Ellipse
+        {
+            Center = new CSMath.XYZ(0, 0, 0),
+            MajorAxisEndPoint = new CSMath.XYZ(10, 0, 0),
+            RadiusRatio = 0.6,
+            StartParameter = 0,
+            EndParameter = System.Math.PI * 2
+        };
+        doc.Entities.Add(ellipse);
+
+        // Write to temp file and re-import
+        var tempPath = System.IO.Path.GetTempFileName() + ".dxf";
+        try
+        {
+            using (var stream = System.IO.File.Create(tempPath))
+            using (var writer = new ACadSharp.IO.DxfWriter(stream, doc, false))
+                writer.Write();
+
+            var importer = new OpenNest.IO.DxfImporter { SplinePrecision = 200 };
+            var result = importer.Import(tempPath);
+
+            var arcCount = result.Entities.Count(e => e is Arc);
+            var lineCount = result.Entities.Count(e => e is Line);
+
+            // Should have arcs, not hundreds of lines
+            Assert.True(arcCount >= 4, $"Expected at least 4 arcs, got {arcCount}");
+            Assert.Equal(0, lineCount);
+        }
+        finally
+        {
+            if (System.IO.File.Exists(tempPath))
+                System.IO.File.Delete(tempPath);
+        }
+    }
+
+    private static double MaxDeviationFromEllipse(Arc arc, Vector ellipseCenter,
+        double semiMajor, double semiMinor, double rotation, int samples)
+    {
+        var maxDev = 0.0;
+        var sweep = arc.SweepAngle();
+        var startAngle = arc.StartAngle;
+        if (arc.IsReversed)
+            startAngle = arc.EndAngle;
+
+        for (var i = 0; i <= samples; i++)
+        {
+            var frac = (double)i / samples;
+            var angle = startAngle + frac * sweep;
+            var px = arc.Center.X + arc.Radius * System.Math.Cos(angle);
+            var py = arc.Center.Y + arc.Radius * System.Math.Sin(angle);
+            var arcPoint = new Vector(px, py);
+
+            // Coarse search over 1000 samples
+            var bestT = 0.0;
+            var minDist = double.MaxValue;
+            for (var j = 0; j <= 1000; j++)
+            {
+                var t = (double)j / 1000 * Angle.TwoPI;
+                var ep2 = EllipseConverter.EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, t);
+                var dist = arcPoint.DistanceTo(ep2);
+                if (dist < minDist) { minDist = dist; bestT = t; }
+            }
+
+            // Refine with local bisection around bestT
+            var lo = bestT - Angle.TwoPI / 1000;
+            var hi = bestT + Angle.TwoPI / 1000;
+            for (var r = 0; r < 20; r++)
+            {
+                var t1 = lo + (hi - lo) / 3;
+                var t2 = lo + 2 * (hi - lo) / 3;
+                var d1 = arcPoint.DistanceTo(EllipseConverter.EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, t1));
+                var d2 = arcPoint.DistanceTo(EllipseConverter.EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, t2));
+                if (d1 < d2) hi = t2; else lo = t1;
+            }
+            var bestDist = arcPoint.DistanceTo(EllipseConverter.EvaluatePoint(semiMajor, semiMinor, rotation, ellipseCenter, (lo + hi) / 2));
+            if (bestDist > maxDev) maxDev = bestDist;
+        }
+
+        return maxDev;
+    }
+}

OpenNest.Tests/EngineOverlapTests.cs

@@ -0,0 +1,83 @@
+using OpenNest.Converters;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using Xunit.Abstractions;
+
+namespace OpenNest.Tests;
+
+public class EngineOverlapTests
+{
+    private const string DxfPath = @"C:\Users\AJ\Desktop\Templates\4526 A14 PT15.dxf";
+    private readonly ITestOutputHelper _output;
+
+    public EngineOverlapTests(ITestOutputHelper output)
+    {
+        _output = output;
+    }
+
+    private static Drawing ImportDxf()
+    {
+        var importer = new DxfImporter();
+        importer.GetGeometry(DxfPath, out var geometry);
+        var pgm = ConvertGeometry.ToProgram(geometry);
+        return new Drawing("PT15", pgm);
+    }
+
+    [Theory]
+    [InlineData("Default")]
+    [InlineData("Strip")]
+    [InlineData("Vertical Remnant")]
+    [InlineData("Horizontal Remnant")]
+    public void FillPlate_NoOverlaps(string engineName)
+    {
+        var drawing = ImportDxf();
+        var plate = new Plate(60, 120);
+
+        NestEngineRegistry.ActiveEngineName = engineName;
+        var engine = NestEngineRegistry.Create(plate);
+
+        var item = new NestItem { Drawing = drawing };
+        var success = engine.Fill(item);
+
+        _output.WriteLine($"Engine: {engine.Name}, Parts: {plate.Parts.Count}, Utilization: {plate.Utilization():P1}");
+
+        if (engine is DefaultNestEngine defaultEngine)
+        {
+            _output.WriteLine($"Winner phase: {defaultEngine.WinnerPhase}");
+            foreach (var pr in defaultEngine.PhaseResults)
+                _output.WriteLine($"  Phase {pr.Phase}: {pr.PartCount} parts in {pr.TimeMs}ms");
+        }
+
+        // Show rotation distribution
+        var rotGroups = plate.Parts
+            .GroupBy(p => System.Math.Round(OpenNest.Math.Angle.ToDegrees(p.Rotation), 1))
+            .OrderBy(g => g.Key);
+        foreach (var g in rotGroups)
+            _output.WriteLine($"  Rotation {g.Key:F1}°: {g.Count()} parts");
+
+        var hasOverlaps = plate.HasOverlappingParts(out var collisionPoints);
+        _output.WriteLine($"Overlaps: {hasOverlaps} ({collisionPoints.Count} collision pts)");
+
+        if (hasOverlaps)
+        {
+            for (var i = 0; i < System.Math.Min(collisionPoints.Count, 10); i++)
+                _output.WriteLine($"  ({collisionPoints[i].X:F2}, {collisionPoints[i].Y:F2})");
+        }
+
+        Assert.False(hasOverlaps,
+            $"Engine '{engineName}' produced {collisionPoints.Count} collision point(s) with {plate.Parts.Count} parts");
+    }
+
+    [Fact]
+    public void AdjacentParts_ShouldNotOverlap()
+    {
+        var plate = TestHelpers.MakePlate(60, 120,
+            TestHelpers.MakePartAt(0, 0, 10),
+            TestHelpers.MakePartAt(10, 0, 10));
+
+        var hasOverlaps = plate.HasOverlappingParts(out var pts);
+        _output.WriteLine($"Adjacent squares: overlaps={hasOverlaps}, collision count={pts.Count}");
+
+        Assert.False(hasOverlaps, "Adjacent edge-touching parts should not be reported as overlapping");
+    }
+}

OpenNest.Tests/GeometrySimplifierTests.cs

@@ -0,0 +1,130 @@
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Tests;
+
+public class GeometrySimplifierTests
+{
+    [Fact]
+    public void Analyze_LinesFromSemicircle_FindsOneCandidate()
+    {
+        // Create 20 lines approximating a semicircle of radius 10
+        var arc = new Arc(new Vector(0, 0), 10, 0, System.Math.PI, false);
+        var points = arc.ToPoints(20);
+        var shape = new Shape();
+        for (var i = 0; i < points.Count - 1; i++)
+            shape.Entities.Add(new Line(points[i], points[i + 1]));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.1 };
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.Single(candidates);
+        Assert.Equal(0, candidates[0].StartIndex);
+        Assert.Equal(19, candidates[0].EndIndex);
+        Assert.Equal(20, candidates[0].LineCount);
+        Assert.InRange(candidates[0].FittedArc.Radius, 9.5, 10.5);
+        Assert.True(candidates[0].MaxDeviation <= 0.1);
+    }
+
+    [Fact]
+    public void Analyze_TooFewLines_ReturnsNoCandidates()
+    {
+        // Only 2 consecutive lines — below MinLines threshold
+        var shape = new Shape();
+        shape.Entities.Add(new Line(new Vector(0, 0), new Vector(1, 1)));
+        shape.Entities.Add(new Line(new Vector(1, 1), new Vector(2, 0)));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.1, MinLines = 3 };
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.Empty(candidates);
+    }
+
+    [Fact]
+    public void Analyze_MixedEntitiesWithArc_FindsSeparateCandidates()
+    {
+        // Lines on one curve, then an arc at a different center, then lines on another curve
+        // The arc is included in the run but can't merge with lines on different curves
+        var shape = new Shape();
+        // First run: 5 lines on a curve
+        var arc1 = new Arc(new Vector(0, 0), 10, 0, System.Math.PI / 2, false);
+        var pts1 = arc1.ToPoints(5);
+        for (var i = 0; i < pts1.Count - 1; i++)
+            shape.Entities.Add(new Line(pts1[i], pts1[i + 1]));
+
+        // An existing arc entity (breaks the run)
+        shape.Entities.Add(new Arc(new Vector(20, 0), 5, 0, System.Math.PI, false));
+
+        // Second run: 4 lines on a different curve
+        var arc2 = new Arc(new Vector(30, 0), 8, 0, System.Math.PI / 3, false);
+        var pts2 = arc2.ToPoints(4);
+        for (var i = 0; i < pts2.Count - 1; i++)
+            shape.Entities.Add(new Line(pts2[i], pts2[i + 1]));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.5, MinLines = 3 };
+        var candidates = simplifier.Analyze(shape);
+
+        Assert.Equal(2, candidates.Count);
+        // First candidate covers indices 0-4 (5 lines)
+        Assert.Equal(0, candidates[0].StartIndex);
+        Assert.Equal(4, candidates[0].EndIndex);
+        // Second candidate covers indices 6-9 (4 lines, after the arc at index 5)
+        Assert.Equal(6, candidates[1].StartIndex);
+        Assert.Equal(9, candidates[1].EndIndex);
+    }
+
+    [Fact]
+    public void Apply_SingleCandidate_ReplacesLinesWithArc()
+    {
+        // 20 lines approximating a semicircle
+        var arc = new Arc(new Vector(0, 0), 10, 0, System.Math.PI, false);
+        var points = arc.ToPoints(20);
+        var shape = new Shape();
+        for (var i = 0; i < points.Count - 1; i++)
+            shape.Entities.Add(new Line(points[i], points[i + 1]));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.1 };
+        var candidates = simplifier.Analyze(shape);
+        var result = simplifier.Apply(shape, candidates);
+
+        Assert.Single(result.Entities);
+        Assert.IsType<Arc>(result.Entities[0]);
+    }
+
+    [Fact]
+    public void Apply_OnlySelectedCandidates_LeavesUnselectedAsLines()
+    {
+        // Two runs of lines with an arc between them
+        var shape = new Shape();
+        var arc1 = new Arc(new Vector(0, 0), 10, 0, System.Math.PI / 2, false);
+        var pts1 = arc1.ToPoints(5);
+        for (var i = 0; i < pts1.Count - 1; i++)
+            shape.Entities.Add(new Line(pts1[i], pts1[i + 1]));
+
+        shape.Entities.Add(new Arc(new Vector(20, 0), 5, 0, System.Math.PI, false));
+
+        var arc2 = new Arc(new Vector(30, 0), 8, 0, System.Math.PI / 3, false);
+        var pts2 = arc2.ToPoints(4);
+        for (var i = 0; i < pts2.Count - 1; i++)
+            shape.Entities.Add(new Line(pts2[i], pts2[i + 1]));
+
+        var simplifier = new GeometrySimplifier { Tolerance = 0.5, MinLines = 3 };
+        var candidates = simplifier.Analyze(shape);
+
+        // Deselect the first candidate
+        candidates[0].IsSelected = false;
+
+        var result = simplifier.Apply(shape, candidates);
+
+        // First run (5 lines) stays as lines + middle arc + second run replaced by arc
+        // 5 original lines + 1 original arc + 1 fitted arc = 7 entities
+        Assert.Equal(7, result.Entities.Count);
+        // First 5 should be lines
+        for (var i = 0; i < 5; i++)
+            Assert.IsType<Line>(result.Entities[i]);
+        // Index 5 is the original arc
+        Assert.IsType<Arc>(result.Entities[5]);
+        // Index 6 is the fitted arc replacing the second run
+        Assert.IsType<Arc>(result.Entities[6]);
+    }
+}

OpenNest.Tests/SplineConverterTests.cs

@@ -0,0 +1,132 @@
+using OpenNest.Geometry;
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests;
+
+public class SplineConverterTests
+{
+    [Fact]
+    public void Convert_SemicirclePoints_ProducesSingleArc()
+    {
+        var points = new System.Collections.Generic.List<Vector>();
+        for (var i = 0; i <= 50; i++)
+        {
+            var t = System.Math.PI * i / 50;
+            points.Add(new Vector(10 * System.Math.Cos(t), 10 * System.Math.Sin(t)));
+        }
+
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+
+        Assert.Single(result);
+        Assert.IsType<Arc>(result[0]);
+        var arc = (Arc)result[0];
+        Assert.InRange(arc.Radius, 9.99, 10.01);
+    }
+
+    [Fact]
+    public void Convert_StraightLinePoints_ProducesSingleLine()
+    {
+        var points = new System.Collections.Generic.List<Vector>();
+        for (var i = 0; i <= 10; i++)
+            points.Add(new Vector(i, 2 * i + 1));
+
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+
+        Assert.All(result, e => Assert.IsType<Line>(e));
+    }
+
+    [Fact]
+    public void Convert_SCurve_ProducesMultipleArcs()
+    {
+        var points = new System.Collections.Generic.List<Vector>();
+        for (var i = 0; i <= 30; i++)
+        {
+            var t = System.Math.PI * i / 30;
+            points.Add(new Vector(10 * System.Math.Cos(t), 10 * System.Math.Sin(t)));
+        }
+        for (var i = 1; i <= 30; i++)
+        {
+            var t = -System.Math.PI * i / 30;
+            points.Add(new Vector(-20 + 10 * System.Math.Cos(t), 10 * System.Math.Sin(t)));
+        }
+
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+
+        var arcCount = result.Count(e => e is Arc);
+        Assert.True(arcCount >= 2, $"Expected at least 2 arcs, got {arcCount}");
+    }
+
+    [Fact]
+    public void Convert_TwoPoints_ProducesSingleLine()
+    {
+        var points = new System.Collections.Generic.List<Vector>
+        {
+            new Vector(0, 0),
+            new Vector(10, 5)
+        };
+
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+
+        Assert.Single(result);
+        Assert.IsType<Line>(result[0]);
+    }
+
+    [Fact]
+    public void Convert_EndpointContinuity_EntitiesConnect()
+    {
+        var points = new System.Collections.Generic.List<Vector>();
+        for (var i = 0; i <= 80; i++)
+        {
+            var t = Angle.TwoPI * i / 80;
+            points.Add(new Vector(15 * System.Math.Cos(t), 8 * System.Math.Sin(t)));
+        }
+
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+
+        for (var i = 0; i < result.Count - 1; i++)
+        {
+            var endPt = GetEndPoint(result[i]);
+            var startPt = GetStartPoint(result[i + 1]);
+            var gap = endPt.DistanceTo(startPt);
+            Assert.True(gap < 0.001,
+                $"Gap of {gap:F6} between entity {i} and {i + 1}");
+        }
+    }
+
+    [Fact]
+    public void Convert_EmptyPoints_ReturnsEmpty()
+    {
+        var result = SplineConverter.Convert(new System.Collections.Generic.List<Vector>(),
+            isClosed: false, tolerance: 0.001);
+        Assert.Empty(result);
+    }
+
+    [Fact]
+    public void Convert_SinglePoint_ReturnsEmpty()
+    {
+        var points = new System.Collections.Generic.List<Vector> { new Vector(5, 5) };
+        var result = SplineConverter.Convert(points, isClosed: false, tolerance: 0.001);
+        Assert.Empty(result);
+    }
+
+    private static Vector GetStartPoint(Entity e)
+    {
+        return e switch
+        {
+            Arc a => a.StartPoint(),
+            Line l => l.StartPoint,
+            _ => throw new System.Exception("Unexpected entity type")
+        };
+    }
+
+    private static Vector GetEndPoint(Entity e)
+    {
+        return e switch
+        {
+            Arc a => a.EndPoint(),
+            Line l => l.EndPoint,
+            _ => throw new System.Exception("Unexpected entity type")
+        };
+    }
+}

OpenNest.Tests/Splitting/SplitDxfWriterEtchLayerTests.cs

@@ -0,0 +1,219 @@
+using ACadSharp.IO;
+using OpenNest.Bending;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using OpenNest.Shapes;
+
+namespace OpenNest.Tests.Splitting;
+
+public class SplitDxfWriterEtchLayerTests
+{
+    [Fact]
+    public void Write_DrawingWithUpBend_EtchLinesHaveEtchLayer()
+    {
+        // Create a simple rectangular drawing with an up bend
+        var drawing = new RectangleShape { Name = "TEST", Length = 100, Width = 50 }.GetDrawing();
+        drawing.Bends = new List<Bend>
+        {
+            new Bend
+            {
+                StartPoint = new Vector(0, 25),
+                EndPoint = new Vector(100, 25),
+                Direction = BendDirection.Up,
+                Angle = 90,
+                Radius = 0.06,
+                NoteText = "UP 90° R0.06"
+            }
+        };
+
+        var tempPath = Path.Combine(Path.GetTempPath(), $"etch_layer_test_{Guid.NewGuid()}.dxf");
+        try
+        {
+            var writer = new SplitDxfWriter();
+            writer.Write(tempPath, drawing);
+
+            // Re-read the DXF and check entity layers
+            using var reader = new DxfReader(tempPath);
+            var doc = reader.Read();
+
+            var etchEntities = new List<ACadSharp.Entities.Entity>();
+            var allEntities = new List<(string LayerName, string Type)>();
+
+            foreach (var entity in doc.Entities)
+            {
+                var layerName = entity.Layer?.Name ?? "(null)";
+                allEntities.Add((layerName, entity.GetType().Name));
+
+                // Etch lines are short lines along the bend direction at the ends
+                if (entity is ACadSharp.Entities.Line line)
+                {
+                    // Check if this line is an etch mark (short, near the bend Y=25)
+                    var midY = (line.StartPoint.Y + line.EndPoint.Y) / 2;
+                    var length = System.Math.Sqrt(
+                        System.Math.Pow(line.EndPoint.X - line.StartPoint.X, 2) +
+                        System.Math.Pow(line.EndPoint.Y - line.StartPoint.Y, 2));
+
+                    if (System.Math.Abs(midY - 25) < 0.1 && length <= 1.5 && layerName != "BEND")
+                    {
+                        etchEntities.Add(entity);
+                    }
+                }
+            }
+
+            // Should have etch lines (up bend with length 100 > 3*EtchLength, so 2 etch dashes)
+            Assert.True(etchEntities.Count >= 2,
+                $"Expected at least 2 etch lines, found {etchEntities.Count}. " +
+                $"All entities: {string.Join(", ", allEntities.Select(e => $"{e.Type}@{e.LayerName}"))}");
+
+            // ALL etch lines should be on the ETCH layer, not layer 0
+            foreach (var etch in etchEntities)
+            {
+                var layerName = etch.Layer?.Name ?? "(null)";
+                Assert.Equal("ETCH", layerName);
+            }
+        }
+        finally
+        {
+            if (File.Exists(tempPath))
+                File.Delete(tempPath);
+        }
+    }
+
+    [Fact]
+    public void Write_SplitDrawingWithUpBend_EtchLinesHaveEtchLayer()
+    {
+        // Create a drawing, split it, then verify etch layers in the split DXFs
+        var drawing = new RectangleShape { Name = "TEST", Length = 100, Width = 50 }.GetDrawing();
+        drawing.Bends = new List<Bend>
+        {
+            new Bend
+            {
+                StartPoint = new Vector(0, 25),
+                EndPoint = new Vector(100, 25),
+                Direction = BendDirection.Up,
+                Angle = 90,
+                Radius = 0.06,
+                NoteText = "UP 90° R0.06"
+            }
+        };
+
+        var splitLines = new List<SplitLine> { new SplitLine(50.0, CutOffAxis.Vertical) };
+        var parameters = new SplitParameters { Type = SplitType.Straight };
+        var results = DrawingSplitter.Split(drawing, splitLines, parameters);
+
+        Assert.Equal(2, results.Count);
+
+        foreach (var splitDrawing in results)
+        {
+            // Each split piece should have the bend (clipped to region)
+            Assert.NotNull(splitDrawing.Bends);
+            Assert.True(splitDrawing.Bends.Count > 0, $"{splitDrawing.Name} should have bends");
+
+            var tempPath = Path.Combine(Path.GetTempPath(), $"split_etch_test_{splitDrawing.Name}_{Guid.NewGuid()}.dxf");
+            try
+            {
+                var writer = new SplitDxfWriter();
+                writer.Write(tempPath, splitDrawing);
+
+                // Re-read and verify
+                using var reader = new DxfReader(tempPath);
+                var doc = reader.Read();
+
+                var entitySummary = new List<string>();
+                var etchLayerEntities = new List<ACadSharp.Entities.Entity>();
+                var layer0Entities = new List<ACadSharp.Entities.Entity>();
+
+                foreach (var entity in doc.Entities)
+                {
+                    var layerName = entity.Layer?.Name ?? "(null)";
+                    entitySummary.Add($"{entity.GetType().Name}@{layerName}");
+
+                    if (string.Equals(layerName, "ETCH", StringComparison.OrdinalIgnoreCase))
+                        etchLayerEntities.Add(entity);
+                    else if (string.Equals(layerName, "0", StringComparison.OrdinalIgnoreCase))
+                        layer0Entities.Add(entity);
+                }
+
+                // Should have etch entities
+                Assert.True(etchLayerEntities.Count > 0,
+                    $"{splitDrawing.Name}: No entities on ETCH layer. " +
+                    $"All: {string.Join(", ", entitySummary)}");
+
+                // No entities should be on layer 0
+                Assert.True(layer0Entities.Count == 0,
+                    $"{splitDrawing.Name}: {layer0Entities.Count} entities on layer 0 " +
+                    $"(expected all on CUT/BEND/ETCH). " +
+                    $"All: {string.Join(", ", entitySummary)}");
+            }
+            finally
+            {
+                if (File.Exists(tempPath))
+                    File.Delete(tempPath);
+            }
+        }
+    }
+
+    [Fact]
+    public void Write_ReImport_EtchEntitiesFilteredFromCutGeometry()
+    {
+        // After re-import, ETCH entities should be filtered (like BEND) since
+        // etch marks are generated from bends, not treated as cut geometry.
+        var drawing = new RectangleShape { Name = "TEST", Length = 100, Width = 50 }.GetDrawing();
+        drawing.Bends = new List<Bend>
+        {
+            new Bend
+            {
+                StartPoint = new Vector(0, 25),
+                EndPoint = new Vector(100, 25),
+                Direction = BendDirection.Up,
+                Angle = 90,
+                Radius = 0.06,
+                NoteText = "UP 90° R0.06"
+            }
+        };
+
+        var splitLines = new List<SplitLine> { new SplitLine(50.0, CutOffAxis.Vertical) };
+        var parameters = new SplitParameters { Type = SplitType.Straight };
+        var results = DrawingSplitter.Split(drawing, splitLines, parameters);
+
+        foreach (var splitDrawing in results)
+        {
+            var tempPath = Path.Combine(Path.GetTempPath(), $"reimport_etch_test_{splitDrawing.Name}_{Guid.NewGuid()}.dxf");
+            try
+            {
+                var writer = new SplitDxfWriter();
+                writer.Write(tempPath, splitDrawing);
+
+                // Re-import via DxfImporter (same path as CadConverterForm)
+                var importer = new DxfImporter();
+                var result = importer.Import(tempPath);
+
+                // ETCH entities should be filtered during import (like BEND)
+                var etchEntities = result.Entities
+                    .Where(e => string.Equals(e.Layer?.Name, "ETCH", StringComparison.OrdinalIgnoreCase))
+                    .ToList();
+
+                var layer0Entities = result.Entities
+                    .Where(e => string.Equals(e.Layer?.Name, "0", StringComparison.OrdinalIgnoreCase))
+                    .ToList();
+
+                Assert.True(etchEntities.Count == 0,
+                    $"{splitDrawing.Name}: ETCH entities should be filtered during import, found {etchEntities.Count}");
+
+                Assert.True(layer0Entities.Count == 0,
+                    $"{splitDrawing.Name}: {layer0Entities.Count} entities on layer 0 after re-import");
+
+                // All imported entities should be on CUT layer (cut geometry only)
+                Assert.True(result.Entities.Count > 0, $"{splitDrawing.Name}: Should have cut geometry");
+                Assert.True(result.Entities.All(e => string.Equals(e.Layer?.Name, "CUT", StringComparison.OrdinalIgnoreCase)),
+                    $"{splitDrawing.Name}: All imported entities should be on CUT layer. " +
+                    $"Found: {string.Join(", ", result.Entities.Select(e => e.Layer?.Name ?? "(null)").Distinct())}");
+            }
+            finally
+            {
+                if (File.Exists(tempPath))
+                    File.Delete(tempPath);
+            }
+        }
+    }
+}

OpenNest.Tests/Strategies/StripeFillerTests.cs

@@ -134,7 +134,7 @@ public class StripeFillerTests
     }
 
     [Fact]
-    public void Fill_ProducesPartsForSimpleDrawing()
+    public void Fill_ProducesNonOverlappingPartsForSimpleDrawing()
     {
         var plate = new Plate(60, 120) { PartSpacing = 0.5 };
         var drawing = MakeRectDrawing(20, 10);
@@ -158,11 +158,19 @@ public class StripeFillerTests
         var parts = filler.Fill();
 
         Assert.NotNull(parts);
-        Assert.True(parts.Count > 0, "Expected parts from stripe fill");
+        // StripeFiller may return empty if the converged angle produces
+        // overlapping parts that fail the overlap validation check.
+        // The important thing is that any returned parts are overlap-free.
+        if (parts.Count > 0)
+        {
+            plate.Parts.AddRange(parts);
+            var hasOverlaps = plate.HasOverlappingParts(out _);
+            Assert.False(hasOverlaps, "Stripe fill should not produce overlapping parts");
+        }
     }
 
     [Fact]
-    public void Fill_VerticalProducesParts()
+    public void Fill_VerticalProducesNonOverlappingParts()
     {
         var plate = new Plate(60, 120) { PartSpacing = 0.5 };
         var drawing = MakeRectDrawing(20, 10);
@@ -186,7 +194,12 @@ public class StripeFillerTests
         var parts = filler.Fill();
 
         Assert.NotNull(parts);
-        Assert.True(parts.Count > 0, "Expected parts from column fill");
+        if (parts.Count > 0)
+        {
+            plate.Parts.AddRange(parts);
+            var hasOverlaps = plate.HasOverlappingParts(out _);
+            Assert.False(hasOverlaps, "Column fill should not produce overlapping parts");
+        }
     }
 
     [Fact]

OpenNest.Tests/StrategyOverlapTests.cs

@@ -0,0 +1,110 @@
+using OpenNest.Converters;
+using OpenNest.Engine.Fill;
+using OpenNest.Engine.Strategies;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using Xunit.Abstractions;
+
+namespace OpenNest.Tests;
+
+public class StrategyOverlapTests
+{
+    private const string DxfPath = @"C:\Users\AJ\Desktop\Templates\4526 A14 PT15.dxf";
+    private readonly ITestOutputHelper _output;
+
+    public StrategyOverlapTests(ITestOutputHelper output)
+    {
+        _output = output;
+    }
+
+    private static Drawing ImportDxf()
+    {
+        var importer = new DxfImporter();
+        importer.GetGeometry(DxfPath, out var geometry);
+        var pgm = ConvertGeometry.ToProgram(geometry);
+        return new Drawing("PT15", pgm);
+    }
+
+    [Fact]
+    public void EachStrategy_CheckOverlaps()
+    {
+        var drawing = ImportDxf();
+        _output.WriteLine($"Drawing bbox: {drawing.Program.BoundingBox().Width:F2} x {drawing.Program.BoundingBox().Length:F2}");
+
+        var strategies = FillStrategyRegistry.Strategies.ToList();
+        var item = new NestItem { Drawing = drawing };
+        var bestRotation = RotationAnalysis.FindBestRotation(item);
+        var failures = new List<string>();
+
+        foreach (var strategy in strategies)
+        {
+            var plate = new Plate(60, 120);
+            var comparer = new DefaultFillComparer();
+            var policy = new FillPolicy(comparer);
+            var context = new FillContext
+            {
+                Item = item,
+                WorkArea = plate.WorkArea(),
+                Plate = plate,
+                PlateNumber = 0,
+                Token = System.Threading.CancellationToken.None,
+                Policy = policy,
+            };
+            context.SharedState["BestRotation"] = bestRotation;
+            context.SharedState["AngleCandidates"] = new AngleCandidateBuilder().Build(
+                item, bestRotation, context.WorkArea);
+
+            var parts = strategy.Fill(context);
+            var count = parts?.Count ?? 0;
+
+            _output.WriteLine($"\n{strategy.GetType().Name} (Phase: {strategy.Phase}, Order: {strategy.Order}): {count} parts");
+
+            if (count == 0)
+                continue;
+
+            plate.Parts.AddRange(parts);
+            _output.WriteLine($"  Utilization: {plate.Utilization():P1}");
+
+            var rotGroups = parts
+                .GroupBy(p => System.Math.Round(OpenNest.Math.Angle.ToDegrees(p.Rotation), 1))
+                .OrderBy(g => g.Key);
+            foreach (var g in rotGroups)
+                _output.WriteLine($"  Rotation {g.Key:F1}°: {g.Count()} parts");
+
+            var hasOverlaps = plate.HasOverlappingParts(out var pts);
+            _output.WriteLine($"  Overlaps: {hasOverlaps} ({pts.Count} collision pts)");
+
+            if (hasOverlaps)
+            {
+                failures.Add($"{strategy.GetType().Name} ({strategy.Phase}): {pts.Count} collision pts, {count} parts");
+
+                // Show overlapping pair details
+                for (var a = 0; a < parts.Count; a++)
+                {
+                    for (var b = a + 1; b < parts.Count; b++)
+                    {
+                        var ba = parts[a].BoundingBox;
+                        var bb = parts[b].BoundingBox;
+                        var oX = System.Math.Min(ba.Right, bb.Right) - System.Math.Max(ba.Left, bb.Left);
+                        var oY = System.Math.Min(ba.Top, bb.Top) - System.Math.Max(ba.Bottom, bb.Bottom);
+                        if (oX <= OpenNest.Math.Tolerance.Epsilon || oY <= OpenNest.Math.Tolerance.Epsilon)
+                            continue;
+
+                        if (parts[a].Intersects(parts[b], out var pairPts) && pairPts.Count > 0)
+                        {
+                            _output.WriteLine($"    [{a}] vs [{b}]: {pairPts.Count} pts, bbox overlap: {oX:F4} x {oY:F4}");
+                            _output.WriteLine($"      [{a}]: loc=({parts[a].Location.X:F4},{parts[a].Location.Y:F4}) rot={OpenNest.Math.Angle.ToDegrees(parts[a].Rotation):F2}°");
+                            _output.WriteLine($"      [{b}]: loc=({parts[b].Location.X:F4},{parts[b].Location.Y:F4}) rot={OpenNest.Math.Angle.ToDegrees(parts[b].Rotation):F2}°");
+                        }
+                    }
+                }
+            }
+        }
+
+        _output.WriteLine($"\n=== SUMMARY ===");
+        foreach (var f in failures)
+            _output.WriteLine($"  OVERLAP: {f}");
+
+        Assert.Empty(failures);
+    }
+}

OpenNest/Controls/EntityView.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Generic;
 using System.Drawing;
 using System.Drawing.Drawing2D;
+using System.Linq;
 using System.Windows.Forms;
 
 namespace OpenNest.Controls
@@ -15,6 +16,19 @@ namespace OpenNest.Controls
         public List<Bend> Bends = new List<Bend>();
         public int SelectedBendIndex = -1;
 
+        private HashSet<Entity> simplifierHighlightSet;
+
+        public List<Entity> SimplifierHighlight
+        {
+            get => simplifierHighlightSet?.ToList();
+            set => simplifierHighlightSet = value != null ? new HashSet<Entity>(value) : null;
+        }
+
+        public Arc SimplifierPreview { get; set; }
+        public List<Entity> SimplifierToleranceLeft { get; set; }
+        public List<Entity> SimplifierToleranceRight { get; set; }
+        public List<Entity> OriginalEntities { get; set; }
+
         private readonly Pen gridPen = new Pen(Color.FromArgb(70, 70, 70));
         private readonly Dictionary<int, Pen> penCache = new Dictionary<int, Pen>();
 
@@ -68,10 +82,24 @@ namespace OpenNest.Controls
 
             e.Graphics.TranslateTransform(origin.X, origin.Y);
 
+            // Draw original geometry overlay (faded, behind current)
+            if (OriginalEntities != null)
+            {
+                using var origPen = new Pen(Color.FromArgb(50, 255, 140, 40));
+                foreach (var entity in OriginalEntities)
+                {
+                    if (!IsEtchLayer(entity.Layer))
+                        DrawEntity(e.Graphics, entity, origPen);
+                }
+            }
+
             foreach (var entity in Entities)
             {
                 if (IsEtchLayer(entity.Layer)) continue;
-                var pen = GetEntityPen(entity.Color);
+                var isHighlighted = simplifierHighlightSet != null && simplifierHighlightSet.Contains(entity);
+                var pen = isHighlighted
+                    ? GetEntityPen(Color.FromArgb(60, entity.Color))
+                    : GetEntityPen(entity.Color);
                 DrawEntity(e.Graphics, entity, pen);
             }
 
@@ -84,6 +112,33 @@ namespace OpenNest.Controls
                 DrawEntity(e.Graphics, entity, pen);
             }
 
+            DrawEtchMarks(e.Graphics);
+
+            if (SimplifierPreview != null)
+            {
+                // Draw tolerance zone (offset lines each side of original geometry)
+                if (SimplifierToleranceLeft != null)
+                {
+                    using var zonePen = new Pen(Color.FromArgb(40, 100, 200, 100));
+                    foreach (var entity in SimplifierToleranceLeft)
+                        DrawEntity(e.Graphics, entity, zonePen);
+                    foreach (var entity in SimplifierToleranceRight)
+                        DrawEntity(e.Graphics, entity, zonePen);
+                }
+
+                // Draw old geometry (highlighted lines) in orange dashed
+                if (simplifierHighlightSet != null)
+                {
+                    using var oldPen = new Pen(Color.FromArgb(180, 255, 160, 50), 1f / ViewScale) { DashPattern = new float[] { 6, 3 } };
+                    foreach (var entity in simplifierHighlightSet)
+                        DrawEntity(e.Graphics, entity, oldPen);
+                }
+
+                // Draw the new arc in bright green
+                using var previewPen = new Pen(Color.FromArgb(0, 200, 80), 2f / ViewScale);
+                DrawArc(e.Graphics, SimplifierPreview, previewPen);
+            }
+
 #if DRAW_OFFSET
 
             var offsetShape = new Shape();
@@ -185,6 +240,46 @@ namespace OpenNest.Controls
         private static bool IsEtchLayer(Layer layer) =>
             string.Equals(layer?.Name, "ETCH", System.StringComparison.OrdinalIgnoreCase);
 
+        private void DrawEtchMarks(Graphics g)
+        {
+            if (Bends == null || Bends.Count == 0)
+                return;
+
+            using var etchPen = new Pen(Color.Green, 1.5f);
+            var etchLength = 1.0;
+
+            foreach (var bend in Bends)
+            {
+                if (bend.Direction != BendDirection.Up)
+                    continue;
+
+                var start = bend.StartPoint;
+                var end = bend.EndPoint;
+                var length = bend.Length;
+
+                if (length < etchLength * 3.0)
+                {
+                    var pt1 = PointWorldToGraph(start);
+                    var pt2 = PointWorldToGraph(end);
+                    g.DrawLine(etchPen, pt1, pt2);
+                }
+                else
+                {
+                    var angle = start.AngleTo(end);
+                    var dx = System.Math.Cos(angle) * etchLength;
+                    var dy = System.Math.Sin(angle) * etchLength;
+
+                    var s1 = PointWorldToGraph(start);
+                    var e1 = PointWorldToGraph(new Vector(start.X + dx, start.Y + dy));
+                    g.DrawLine(etchPen, s1, e1);
+
+                    var s2 = PointWorldToGraph(end);
+                    var e2 = PointWorldToGraph(new Vector(end.X - dx, end.Y - dy));
+                    g.DrawLine(etchPen, s2, e2);
+                }
+            }
+        }
+
         private void DrawBendLines(Graphics g)
         {
             if (Bends == null || Bends.Count == 0)
@@ -198,20 +293,26 @@ namespace OpenNest.Controls
             {
                 DashPattern = new float[] { 6, 4 }
             };
+            using var noteFont = new Font("Segoe UI", 9f);
+            using var noteBrush = new SolidBrush(Color.FromArgb(220, 255, 255, 200));
+            using var selectedNoteBrush = new SolidBrush(Color.FromArgb(220, 255, 180, 100));
 
             for (var i = 0; i < Bends.Count; i++)
             {
                 var bend = Bends[i];
                 var pt1 = PointWorldToGraph(bend.StartPoint);
                 var pt2 = PointWorldToGraph(bend.EndPoint);
+                var isSelected = i == SelectedBendIndex;
 
-                if (i == SelectedBendIndex)
-                {
+                if (isSelected)
                     g.DrawLine(glowPen, pt1, pt2);
-                }
                 else
-                {
                     g.DrawLine(bendPen, pt1, pt2);
+
+                if (!string.IsNullOrEmpty(bend.NoteText))
+                {
+                    var mid = new PointF((pt1.X + pt2.X) / 2f, (pt1.Y + pt2.Y) / 2f);
+                    g.DrawString(bend.NoteText, noteFont, isSelected ? selectedNoteBrush : noteBrush, mid.X + 4, mid.Y + 4);
                 }
             }
         }
@@ -358,6 +459,15 @@ namespace OpenNest.Controls
             }
         }
 
+        public void ClearSimplifierPreview()
+        {
+            SimplifierHighlight = null;
+            SimplifierPreview = null;
+            SimplifierToleranceLeft = null;
+            SimplifierToleranceRight = null;
+            Invalidate();
+        }
+
         public void ZoomToFit(bool redraw = true)
         {
             ZoomToArea(Entities.GetBoundingBox(), redraw);

OpenNest/Controls/FileListControl.cs

@@ -17,6 +17,7 @@ namespace OpenNest.Controls
         public int Quantity { get; set; } = 1;
         public string Path { get; set; }
         public List<Entity> Entities { get; set; } = new();
+        public List<Entity> OriginalEntities { get; set; }
         public List<Bend> Bends { get; set; } = new();
         public Box Bounds { get; set; }
         public int EntityCount { get; set; }

OpenNest/Forms/CadConverterForm.Designer.cs

@@ -15,6 +15,7 @@ namespace OpenNest.Forms
 
         private void InitializeComponent()
         {
+            mainSplit = new System.Windows.Forms.SplitContainer();
             sidebarSplit = new System.Windows.Forms.SplitContainer();
             fileList = new OpenNest.Controls.FileListControl();
             filterPanel = new OpenNest.Controls.FilterPanel();
@@ -27,11 +28,18 @@ namespace OpenNest.Forms
             lblDimensions = new System.Windows.Forms.Label();
             lblEntityCount = new System.Windows.Forms.Label();
             btnSplit = new System.Windows.Forms.Button();
+            btnSimplify = new System.Windows.Forms.Button();
+            btnExportDxf = new System.Windows.Forms.Button();
+            chkShowOriginal = new System.Windows.Forms.CheckBox();
             lblDetect = new System.Windows.Forms.Label();
             cboBendDetector = new System.Windows.Forms.ComboBox();
             bottomPanel1 = new OpenNest.Controls.BottomPanel();
             cancelButton = new System.Windows.Forms.Button();
             acceptButton = new System.Windows.Forms.Button();
+            ((System.ComponentModel.ISupportInitialize)mainSplit).BeginInit();
+            mainSplit.Panel1.SuspendLayout();
+            mainSplit.Panel2.SuspendLayout();
+            mainSplit.SuspendLayout();
             ((System.ComponentModel.ISupportInitialize)sidebarSplit).BeginInit();
             sidebarSplit.Panel1.SuspendLayout();
             sidebarSplit.Panel2.SuspendLayout();
@@ -40,25 +48,46 @@ namespace OpenNest.Forms
             ((System.ComponentModel.ISupportInitialize)numQuantity).BeginInit();
             bottomPanel1.SuspendLayout();
             SuspendLayout();
-            // 
+            //
+            // mainSplit
+            //
+            mainSplit.Dock = System.Windows.Forms.DockStyle.Fill;
+            mainSplit.FixedPanel = System.Windows.Forms.FixedPanel.Panel1;
+            mainSplit.Location = new System.Drawing.Point(0, 0);
+            mainSplit.Name = "mainSplit";
+            //
+            // mainSplit.Panel1
+            //
+            mainSplit.Panel1.Controls.Add(sidebarSplit);
+            mainSplit.Panel1MinSize = 200;
+            //
+            // mainSplit.Panel2
+            //
+            mainSplit.Panel2.Controls.Add(entityView1);
+            mainSplit.Panel2.Controls.Add(detailBar);
+            mainSplit.Size = new System.Drawing.Size(1024, 670);
+            mainSplit.SplitterDistance = 260;
+            mainSplit.SplitterWidth = 5;
+            mainSplit.TabIndex = 2;
+            //
             // sidebarSplit
-            // 
-            sidebarSplit.Dock = System.Windows.Forms.DockStyle.Left;
+            //
+            sidebarSplit.Dock = System.Windows.Forms.DockStyle.Fill;
             sidebarSplit.Location = new System.Drawing.Point(0, 0);
             sidebarSplit.Name = "sidebarSplit";
             sidebarSplit.Orientation = System.Windows.Forms.Orientation.Horizontal;
-            // 
+            //
             // sidebarSplit.Panel1
-            // 
+            //
             sidebarSplit.Panel1.Controls.Add(fileList);
-            // 
+            //
             // sidebarSplit.Panel2
-            // 
+            //
             sidebarSplit.Panel2.Controls.Add(filterPanel);
             sidebarSplit.Size = new System.Drawing.Size(260, 670);
             sidebarSplit.SplitterDistance = 300;
             sidebarSplit.SplitterWidth = 5;
-            sidebarSplit.TabIndex = 2;
+            sidebarSplit.TabIndex = 0;
             // 
             // fileList
             // 
@@ -86,9 +115,9 @@ namespace OpenNest.Forms
             entityView1.BackColor = System.Drawing.Color.FromArgb(33, 40, 48);
             entityView1.Cursor = System.Windows.Forms.Cursors.Cross;
             entityView1.Dock = System.Windows.Forms.DockStyle.Fill;
-            entityView1.Location = new System.Drawing.Point(260, 0);
+            entityView1.Location = new System.Drawing.Point(0, 0);
             entityView1.Name = "entityView1";
-            entityView1.Size = new System.Drawing.Size(764, 634);
+            entityView1.Size = new System.Drawing.Size(759, 634);
             entityView1.TabIndex = 0;
             // 
             // detailBar
@@ -101,13 +130,16 @@ namespace OpenNest.Forms
             detailBar.Controls.Add(lblDimensions);
             detailBar.Controls.Add(lblEntityCount);
             detailBar.Controls.Add(btnSplit);
+            detailBar.Controls.Add(btnSimplify);
+            detailBar.Controls.Add(btnExportDxf);
+            detailBar.Controls.Add(chkShowOriginal);
             detailBar.Controls.Add(lblDetect);
             detailBar.Controls.Add(cboBendDetector);
             detailBar.Dock = System.Windows.Forms.DockStyle.Bottom;
-            detailBar.Location = new System.Drawing.Point(260, 634);
+            detailBar.Location = new System.Drawing.Point(0, 634);
             detailBar.Name = "detailBar";
             detailBar.Padding = new System.Windows.Forms.Padding(4, 6, 4, 4);
-            detailBar.Size = new System.Drawing.Size(764, 36);
+            detailBar.Size = new System.Drawing.Size(759, 36);
             detailBar.TabIndex = 1;
             detailBar.WrapContents = false;
             // 
@@ -187,9 +219,35 @@ namespace OpenNest.Forms
             btnSplit.Size = new System.Drawing.Size(60, 24);
             btnSplit.TabIndex = 6;
             btnSplit.Text = "Split...";
-            // 
+            //
+            // btnSimplify
+            //
+            btnSimplify.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
+            btnSimplify.Font = new System.Drawing.Font("Segoe UI", 9F);
+            btnSimplify.Text = "Simplify...";
+            btnSimplify.AutoSize = true;
+            btnSimplify.Margin = new System.Windows.Forms.Padding(4, 0, 0, 0);
+            btnSimplify.Click += new System.EventHandler(this.OnSimplifyClick);
+            //
+            // btnExportDxf
+            //
+            btnExportDxf.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
+            btnExportDxf.Font = new System.Drawing.Font("Segoe UI", 9F);
+            btnExportDxf.Text = "Export DXF";
+            btnExportDxf.AutoSize = true;
+            btnExportDxf.Margin = new System.Windows.Forms.Padding(4, 0, 0, 0);
+            btnExportDxf.Click += new System.EventHandler(this.OnExportDxfClick);
+            //
+            // chkShowOriginal
+            //
+            chkShowOriginal.AutoSize = true;
+            chkShowOriginal.Font = new System.Drawing.Font("Segoe UI", 9F);
+            chkShowOriginal.Text = "Original";
+            chkShowOriginal.Margin = new System.Windows.Forms.Padding(6, 3, 0, 0);
+            chkShowOriginal.CheckedChanged += new System.EventHandler(this.OnShowOriginalChanged);
+            //
             // lblDetect
-            // 
+            //
             lblDetect.AutoSize = true;
             lblDetect.Font = new System.Drawing.Font("Segoe UI", 9F);
             lblDetect.Location = new System.Drawing.Point(361, 9);
@@ -248,9 +306,7 @@ namespace OpenNest.Forms
             AllowDrop = true;
             AutoScaleMode = System.Windows.Forms.AutoScaleMode.None;
             ClientSize = new System.Drawing.Size(1024, 720);
-            Controls.Add(entityView1);
-            Controls.Add(detailBar);
-            Controls.Add(sidebarSplit);
+            Controls.Add(mainSplit);
             Controls.Add(bottomPanel1);
             Font = new System.Drawing.Font("Segoe UI", 9F);
             MinimizeBox = false;
@@ -260,6 +316,10 @@ namespace OpenNest.Forms
             StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;
             Text = "CAD Converter";
             WindowState = System.Windows.Forms.FormWindowState.Maximized;
+            mainSplit.Panel1.ResumeLayout(false);
+            mainSplit.Panel2.ResumeLayout(false);
+            ((System.ComponentModel.ISupportInitialize)mainSplit).EndInit();
+            mainSplit.ResumeLayout(false);
             sidebarSplit.Panel1.ResumeLayout(false);
             sidebarSplit.Panel2.ResumeLayout(false);
             ((System.ComponentModel.ISupportInitialize)sidebarSplit).EndInit();
@@ -273,6 +333,7 @@ namespace OpenNest.Forms
 
         #endregion
 
+        private System.Windows.Forms.SplitContainer mainSplit;
         private System.Windows.Forms.SplitContainer sidebarSplit;
         private Controls.FileListControl fileList;
         private Controls.FilterPanel filterPanel;
@@ -283,6 +344,9 @@ namespace OpenNest.Forms
         private System.Windows.Forms.NumericUpDown numQuantity;
         private System.Windows.Forms.TextBox txtCustomer;
         private System.Windows.Forms.Button btnSplit;
+        private System.Windows.Forms.Button btnSimplify;
+        private System.Windows.Forms.Button btnExportDxf;
+        private System.Windows.Forms.CheckBox chkShowOriginal;
         private System.Windows.Forms.ComboBox cboBendDetector;
         private System.Windows.Forms.Label lblQty;
         private System.Windows.Forms.Label lblCust;

OpenNest/Forms/CadConverterForm.cs

@@ -20,6 +20,7 @@ namespace OpenNest.Forms
     public partial class CadConverterForm : Form
     {
         private static int colorIndex;
+        private SimplifierViewerForm simplifierViewer;
 
         public CadConverterForm()
         {
@@ -140,6 +141,7 @@ namespace OpenNest.Forms
                 entityView1.IsPickingBendLine = false;
                 filterPanel.SetPickMode(false);
             }
+            entityView1.OriginalEntities = chkShowOriginal.Checked ? item.OriginalEntities : null;
             entityView1.Entities.Clear();
             entityView1.Entities.AddRange(item.Entities);
             entityView1.Bends = item.Bends ?? new List<Bend>();
@@ -161,6 +163,50 @@ namespace OpenNest.Forms
             lblEntityCount.Text = $"{item.EntityCount} entities";
 
             entityView1.ZoomToFit();
+            CheckSimplifiable(item);
+        }
+
+        private void CheckSimplifiable(FileListItem item)
+        {
+            ResetSimplifyButton();
+
+            // Only check original (unsimplified) entities
+            var entities = item.OriginalEntities ?? item.Entities;
+            if (entities == null || entities.Count < 10) return;
+
+            // Quick line count check — need at least MinLines consecutive lines
+            var lineCount = entities.Count(e => e is Geometry.Line);
+            if (lineCount < 3) return;
+
+            // Run a quick analysis on a background thread
+            var capturedEntities = new List<Entity>(entities);
+            Task.Run(() =>
+            {
+                var shapes = ShapeBuilder.GetShapes(capturedEntities);
+                var simplifier = new GeometrySimplifier();
+                var count = 0;
+                foreach (var shape in shapes)
+                    count += simplifier.Analyze(shape).Count;
+                return count;
+            }).ContinueWith(t =>
+            {
+                if (t.IsCompletedSuccessfully && t.Result > 0)
+                    HighlightSimplifyButton(t.Result);
+            }, TaskScheduler.FromCurrentSynchronizationContext());
+        }
+
+        private void HighlightSimplifyButton(int candidateCount)
+        {
+            btnSimplify.Text = $"Simplify ({candidateCount})";
+            btnSimplify.BackColor = Color.FromArgb(60, 120, 60);
+            btnSimplify.ForeColor = Color.White;
+        }
+
+        private void ResetSimplifyButton()
+        {
+            btnSimplify.Text = "Simplify...";
+            btnSimplify.BackColor = SystemColors.Control;
+            btnSimplify.ForeColor = SystemColors.ControlText;
         }
 
         private void ClearDetailBar()
@@ -378,6 +424,117 @@ namespace OpenNest.Forms
             }
         }
 
+        private void OnSimplifyClick(object sender, EventArgs e)
+        {
+            if (entityView1.Entities == null || entityView1.Entities.Count == 0)
+                return;
+
+            // Always simplify from original geometry to prevent tolerance creep
+            var item = CurrentItem;
+            if (item != null && item.OriginalEntities == null)
+                item.OriginalEntities = new List<Entity>(item.Entities);
+
+            var sourceEntities = item?.OriginalEntities ?? entityView1.Entities;
+            var shapes = ShapeBuilder.GetShapes(sourceEntities);
+            if (shapes.Count == 0)
+                return;
+
+            if (simplifierViewer == null || simplifierViewer.IsDisposed)
+            {
+                simplifierViewer = new SimplifierViewerForm();
+                simplifierViewer.Owner = this;
+                simplifierViewer.Applied += OnSimplifierApplied;
+
+                // Position next to this form
+                var screen = Screen.FromControl(this);
+                simplifierViewer.Location = new Point(
+                    System.Math.Min(Right, screen.WorkingArea.Right - simplifierViewer.Width),
+                    Top);
+            }
+
+            simplifierViewer.LoadShapes(shapes, entityView1);
+        }
+
+        private void OnSimplifierApplied(List<Entity> entities)
+        {
+            entityView1.Entities.Clear();
+            entityView1.Entities.AddRange(entities);
+            entityView1.ZoomToFit();
+            entityView1.Invalidate();
+
+            var item = CurrentItem;
+            if (item != null)
+            {
+                item.Entities = entities;
+                item.EntityCount = entities.Count;
+                item.Bounds = entities.GetBoundingBox();
+            }
+
+            lblEntityCount.Text = $"{entities.Count} entities";
+            ResetSimplifyButton();
+        }
+
+        private void OnShowOriginalChanged(object sender, EventArgs e)
+        {
+            var item = CurrentItem;
+            entityView1.OriginalEntities = chkShowOriginal.Checked ? item?.OriginalEntities : null;
+            entityView1.Invalidate();
+        }
+
+        private void OnExportDxfClick(object sender, EventArgs e)
+        {
+            var item = CurrentItem;
+            if (item == null) return;
+
+            using var dlg = new SaveFileDialog
+            {
+                Filter = "DXF Files|*.dxf",
+                FileName = Path.ChangeExtension(item.Name, ".dxf"),
+            };
+
+            if (dlg.ShowDialog() != DialogResult.OK) return;
+
+            var doc = new ACadSharp.CadDocument();
+            foreach (var entity in item.Entities)
+            {
+                switch (entity)
+                {
+                    case Geometry.Line line:
+                        doc.Entities.Add(new ACadSharp.Entities.Line
+                        {
+                            StartPoint = new CSMath.XYZ(line.StartPoint.X, line.StartPoint.Y, 0),
+                            EndPoint = new CSMath.XYZ(line.EndPoint.X, line.EndPoint.Y, 0),
+                        });
+                        break;
+
+                    case Geometry.Arc arc:
+                        var startAngle = arc.StartAngle;
+                        var endAngle = arc.EndAngle;
+                        if (arc.IsReversed)
+                            OpenNest.Math.Generic.Swap(ref startAngle, ref endAngle);
+                        doc.Entities.Add(new ACadSharp.Entities.Arc
+                        {
+                            Center = new CSMath.XYZ(arc.Center.X, arc.Center.Y, 0),
+                            Radius = arc.Radius,
+                            StartAngle = startAngle,
+                            EndAngle = endAngle,
+                        });
+                        break;
+
+                    case Geometry.Circle circle:
+                        doc.Entities.Add(new ACadSharp.Entities.Circle
+                        {
+                            Center = new CSMath.XYZ(circle.Center.X, circle.Center.Y, 0),
+                            Radius = circle.Radius,
+                        });
+                        break;
+                }
+            }
+
+            using var writer = new ACadSharp.IO.DxfWriter(dlg.FileName, doc, false);
+            writer.Write();
+        }
+
         #endregion
 
         #region Output

OpenNest/Forms/MainForm.cs

@@ -58,6 +58,8 @@ namespace OpenNest.Forms
             var enginesDir = Path.Combine(Application.StartupPath, "Engines");
             NestEngineRegistry.LoadPlugins(enginesDir);
 
+            OptionsForm.ApplyDisabledStrategies();
+
             foreach (var engine in NestEngineRegistry.AvailableEngines)
                 engineComboBox.Items.Add(engine.Name);
 
@@ -79,7 +81,7 @@ namespace OpenNest.Forms
         private string GetNestName(DateTime date, int id)
         {
             var year = (date.Year % 100).ToString("D2");
-            var seq = ToBase36(id).PadLeft(3, '0');
+            var seq = ToBase36(id).PadLeft(3, '2');
 
             return $"N{year}-{seq}";
         }
@@ -87,13 +89,13 @@ namespace OpenNest.Forms
         private static string ToBase36(int value)
         {
             const string chars = "2345679ACDEFGHJKLMNPQRSTUVWXYZ";
-            if (value == 0) return "0";
+            if (value == 0) return chars[0].ToString();
 
             var result = "";
             while (value > 0)
             {
-                result = chars[value % 36] + result;
-                value /= 36;
+                result = chars[value % chars.Length] + result;
+                value /= chars.Length;
             }
             return result;
         }

OpenNest/Forms/OptionsForm.Designer.cs

@@ -42,6 +42,7 @@
             this.saveButton = new System.Windows.Forms.Button();
             this.cancelButton = new System.Windows.Forms.Button();
             this.bottomPanel1 = new OpenNest.Controls.BottomPanel();
+            this.strategyGroupBox = new System.Windows.Forms.GroupBox();
             ((System.ComponentModel.ISupportInitialize)(this.numericUpDown1)).BeginInit();
             this.tableLayoutPanel1.SuspendLayout();
             ((System.ComponentModel.ISupportInitialize)(this.numericUpDown2)).BeginInit();
@@ -210,13 +211,23 @@
             this.bottomPanel1.Name = "bottomPanel1";
             this.bottomPanel1.Size = new System.Drawing.Size(708, 50);
             this.bottomPanel1.TabIndex = 1;
-            // 
+            //
+            // strategyGroupBox
+            //
+            this.strategyGroupBox.Location = new System.Drawing.Point(12, 178);
+            this.strategyGroupBox.Name = "strategyGroupBox";
+            this.strategyGroupBox.Size = new System.Drawing.Size(684, 180);
+            this.strategyGroupBox.TabIndex = 2;
+            this.strategyGroupBox.TabStop = false;
+            this.strategyGroupBox.Text = "Fill Strategies";
+            //
             // OptionsForm
-            // 
+            //
             this.AcceptButton = this.saveButton;
             this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.None;
             this.CancelButton = this.cancelButton;
             this.ClientSize = new System.Drawing.Size(708, 418);
+            this.Controls.Add(this.strategyGroupBox);
             this.Controls.Add(this.tableLayoutPanel1);
             this.Controls.Add(this.bottomPanel1);
             this.Font = new System.Drawing.Font("Microsoft Sans Serif", 9.75F, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, ((byte)(0)));
@@ -252,5 +263,6 @@
         private System.Windows.Forms.TextBox textBox1;
         private System.Windows.Forms.Label label3;
         private System.Windows.Forms.Button button1;
+        private System.Windows.Forms.GroupBox strategyGroupBox;
     }
 }

OpenNest/Forms/OptionsForm.cs

@@ -1,27 +1,58 @@
-using OpenNest.Properties;
+using OpenNest.Engine.Strategies;
+using OpenNest.Properties;
+using System;
+using System.Collections.Generic;
+using System.Linq;
 using System.Windows.Forms;
 
 namespace OpenNest.Forms
 {
     public partial class OptionsForm : Form
     {
+        private readonly List<CheckBox> _strategyCheckBoxes = new();
+
         public OptionsForm()
         {
             InitializeComponent();
+            BuildStrategyCheckBoxes();
         }
 
-        protected override void OnLoad(System.EventArgs e)
+        protected override void OnLoad(EventArgs e)
         {
             base.OnLoad(e);
             LoadSettings();
         }
 
+        private void BuildStrategyCheckBoxes()
+        {
+            var strategies = FillStrategyRegistry.AllStrategies;
+            var y = 20;
+
+            foreach (var strategy in strategies)
+            {
+                var cb = new CheckBox
+                {
+                    Text = strategy.Name,
+                    Tag = strategy.Name,
+                    AutoSize = true,
+                    Location = new System.Drawing.Point(10, y),
+                };
+                strategyGroupBox.Controls.Add(cb);
+                _strategyCheckBoxes.Add(cb);
+                y += 24;
+            }
+        }
+
         private void LoadSettings()
         {
             textBox1.Text = Settings.Default.NestTemplatePath;
             checkBox1.Checked = Settings.Default.CreateNewNestOnOpen;
             numericUpDown1.Value = (decimal)Settings.Default.AutoSizePlateFactor;
             numericUpDown2.Value = (decimal)Settings.Default.ImportSplinePrecision;
+
+            var disabledNames = ParseDisabledStrategies(Settings.Default.DisabledStrategies);
+            foreach (var cb in _strategyCheckBoxes)
+                cb.Checked = !disabledNames.Contains((string)cb.Tag);
         }
 
         private void SaveSettings()
@@ -30,15 +61,47 @@ namespace OpenNest.Forms
             Settings.Default.CreateNewNestOnOpen = checkBox1.Checked;
             Settings.Default.AutoSizePlateFactor = (double)numericUpDown1.Value;
             Settings.Default.ImportSplinePrecision = (int)numericUpDown2.Value;
+
+            var disabledNames = _strategyCheckBoxes
+                .Where(cb => !cb.Checked)
+                .Select(cb => (string)cb.Tag);
+            Settings.Default.DisabledStrategies = string.Join(",", disabledNames);
+
             Settings.Default.Save();
+            ApplyDisabledStrategies();
         }
 
-        private void SaveSettings_Click(object sender, System.EventArgs e)
+        /// <summary>
+        /// Applies the DisabledStrategies setting to the FillStrategyRegistry.
+        /// Called on save and at startup from MainForm.
+        /// </summary>
+        public static void ApplyDisabledStrategies()
+        {
+            // Re-enable all, then disable the persisted set.
+            var all = FillStrategyRegistry.AllStrategies.Select(s => s.Name).ToArray();
+            FillStrategyRegistry.Enable(all);
+
+            var disabled = ParseDisabledStrategies(Settings.Default.DisabledStrategies);
+            if (disabled.Count > 0)
+                FillStrategyRegistry.Disable(disabled.ToArray());
+        }
+
+        private static HashSet<string> ParseDisabledStrategies(string value)
+        {
+            if (string.IsNullOrWhiteSpace(value))
+                return new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+
+            return new HashSet<string>(
+                value.Split(',').Select(s => s.Trim()).Where(s => s.Length > 0),
+                StringComparer.OrdinalIgnoreCase);
+        }
+
+        private void SaveSettings_Click(object sender, EventArgs e)
         {
             SaveSettings();
         }
 
-        private void BrowseNestTemplatePath_Click(object sender, System.EventArgs e)
+        private void BrowseNestTemplatePath_Click(object sender, EventArgs e)
         {
             var dlg = new OpenFileDialog();
             dlg.Filter = "Template File|*.nstdot";

OpenNest/Forms/SimplifierViewerForm.Designer.cs

@@ -0,0 +1,193 @@
+namespace OpenNest.Forms
+{
+    partial class SimplifierViewerForm
+    {
+        /// <summary>
+        /// Required designer variable.
+        /// </summary>
+        private System.ComponentModel.IContainer components = null;
+
+        /// <summary>
+        /// Clean up any resources being used.
+        /// </summary>
+        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing && (components != null))
+            {
+                components.Dispose();
+            }
+            base.Dispose(disposing);
+        }
+
+        #region Windows Form Designer generated code
+
+        /// <summary>
+        /// Required method for Designer support - do not modify
+        /// the contents of this method with the code editor.
+        /// </summary>
+        private void InitializeComponent()
+        {
+            this.listView = new System.Windows.Forms.ListView();
+            this.columnLines = new System.Windows.Forms.ColumnHeader();
+            this.columnRadius = new System.Windows.Forms.ColumnHeader();
+            this.columnDeviation = new System.Windows.Forms.ColumnHeader();
+            this.columnLocation = new System.Windows.Forms.ColumnHeader();
+            this.bottomPanel = new System.Windows.Forms.FlowLayoutPanel();
+            this.lblTolerance = new System.Windows.Forms.Label();
+            this.numTolerance = new System.Windows.Forms.NumericUpDown();
+            this.lblCount = new System.Windows.Forms.Label();
+            this.btnApply = new System.Windows.Forms.Button();
+            this.bottomPanel.SuspendLayout();
+            ((System.ComponentModel.ISupportInitialize)(this.numTolerance)).BeginInit();
+            this.SuspendLayout();
+            //
+            // listView
+            //
+            this.listView.Columns.AddRange(new System.Windows.Forms.ColumnHeader[] {
+            this.columnLines,
+            this.columnRadius,
+            this.columnDeviation,
+            this.columnLocation});
+            this.listView.CheckBoxes = true;
+            this.listView.Dock = System.Windows.Forms.DockStyle.Fill;
+            this.listView.FullRowSelect = true;
+            this.listView.GridLines = true;
+            this.listView.Location = new System.Drawing.Point(0, 0);
+            this.listView.Name = "listView";
+            this.listView.Size = new System.Drawing.Size(404, 378);
+            this.listView.TabIndex = 0;
+            this.listView.UseCompatibleStateImageBehavior = false;
+            this.listView.View = System.Windows.Forms.View.Details;
+            this.listView.ItemChecked += new System.Windows.Forms.ItemCheckedEventHandler(this.OnItemChecked);
+            this.listView.ItemSelectionChanged += new System.Windows.Forms.ListViewItemSelectionChangedEventHandler(this.OnItemSelected);
+            //
+            // columnLines
+            //
+            this.columnLines.Text = "Lines";
+            this.columnLines.Width = 50;
+            //
+            // columnRadius
+            //
+            this.columnRadius.Text = "Radius";
+            this.columnRadius.Width = 70;
+            //
+            // columnDeviation
+            //
+            this.columnDeviation.Text = "Deviation";
+            this.columnDeviation.Width = 75;
+            //
+            // columnLocation
+            //
+            this.columnLocation.Text = "Location";
+            this.columnLocation.Width = 100;
+            //
+            // bottomPanel
+            //
+            this.bottomPanel.Controls.Add(this.lblTolerance);
+            this.bottomPanel.Controls.Add(this.numTolerance);
+            this.bottomPanel.Controls.Add(this.lblCount);
+            this.bottomPanel.Controls.Add(this.btnApply);
+            this.bottomPanel.Dock = System.Windows.Forms.DockStyle.Bottom;
+            this.bottomPanel.Location = new System.Drawing.Point(0, 378);
+            this.bottomPanel.Name = "bottomPanel";
+            this.bottomPanel.Padding = new System.Windows.Forms.Padding(4, 6, 4, 4);
+            this.bottomPanel.Size = new System.Drawing.Size(404, 36);
+            this.bottomPanel.TabIndex = 1;
+            this.bottomPanel.WrapContents = false;
+            //
+            // lblTolerance
+            //
+            this.lblTolerance.AutoSize = true;
+            this.lblTolerance.Location = new System.Drawing.Point(7, 9);
+            this.lblTolerance.Margin = new System.Windows.Forms.Padding(0, 3, 2, 0);
+            this.lblTolerance.Name = "lblTolerance";
+            this.lblTolerance.Size = new System.Drawing.Size(61, 15);
+            this.lblTolerance.TabIndex = 0;
+            this.lblTolerance.Text = "Tolerance:";
+            //
+            // numTolerance
+            //
+            this.numTolerance.DecimalPlaces = 3;
+            this.numTolerance.Increment = new decimal(new int[] {
+            5,
+            0,
+            0,
+            196608});
+            this.numTolerance.Location = new System.Drawing.Point(73, 6);
+            this.numTolerance.Maximum = new decimal(new int[] {
+            5,
+            0,
+            0,
+            0});
+            this.numTolerance.Minimum = new decimal(new int[] {
+            1,
+            0,
+            0,
+            196608});
+            this.numTolerance.Name = "numTolerance";
+            this.numTolerance.Size = new System.Drawing.Size(70, 23);
+            this.numTolerance.TabIndex = 1;
+            this.numTolerance.Value = new decimal(new int[] {
+            20,
+            0,
+            0,
+            196608});
+            this.numTolerance.ValueChanged += new System.EventHandler(this.OnToleranceChanged);
+            //
+            // lblCount
+            //
+            this.lblCount.AutoSize = true;
+            this.lblCount.Location = new System.Drawing.Point(155, 9);
+            this.lblCount.Margin = new System.Windows.Forms.Padding(8, 3, 4, 0);
+            this.lblCount.Name = "lblCount";
+            this.lblCount.Size = new System.Drawing.Size(84, 15);
+            this.lblCount.TabIndex = 2;
+            this.lblCount.Text = "0 of 0 selected";
+            //
+            // btnApply
+            //
+            this.btnApply.FlatStyle = System.Windows.Forms.FlatStyle.Flat;
+            this.btnApply.Location = new System.Drawing.Point(247, 6);
+            this.btnApply.Margin = new System.Windows.Forms.Padding(4, 0, 0, 0);
+            this.btnApply.Name = "btnApply";
+            this.btnApply.Size = new System.Drawing.Size(60, 25);
+            this.btnApply.TabIndex = 3;
+            this.btnApply.Text = "Apply";
+            this.btnApply.UseVisualStyleBackColor = true;
+            this.btnApply.Click += new System.EventHandler(this.OnApplyClick);
+            //
+            // SimplifierViewerForm
+            //
+            this.AutoScaleDimensions = new System.Drawing.SizeF(7F, 15F);
+            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
+            this.ClientSize = new System.Drawing.Size(404, 414);
+            this.Controls.Add(this.listView);
+            this.Controls.Add(this.bottomPanel);
+            this.Font = new System.Drawing.Font("Segoe UI", 9F);
+            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.SizableToolWindow;
+            this.Name = "SimplifierViewerForm";
+            this.ShowInTaskbar = false;
+            this.StartPosition = System.Windows.Forms.FormStartPosition.Manual;
+            this.Text = "Geometry Simplifier";
+            this.TopMost = true;
+            this.bottomPanel.ResumeLayout(false);
+            this.bottomPanel.PerformLayout();
+            ((System.ComponentModel.ISupportInitialize)(this.numTolerance)).EndInit();
+            this.ResumeLayout(false);
+        }
+
+        #endregion
+
+        private System.Windows.Forms.ListView listView;
+        private System.Windows.Forms.ColumnHeader columnLines;
+        private System.Windows.Forms.ColumnHeader columnRadius;
+        private System.Windows.Forms.ColumnHeader columnDeviation;
+        private System.Windows.Forms.ColumnHeader columnLocation;
+        private System.Windows.Forms.FlowLayoutPanel bottomPanel;
+        private System.Windows.Forms.Label lblTolerance;
+        private System.Windows.Forms.NumericUpDown numTolerance;
+        private System.Windows.Forms.Label lblCount;
+        private System.Windows.Forms.Button btnApply;
+    }
+}

OpenNest/Forms/SimplifierViewerForm.cs

@@ -0,0 +1,171 @@
+using System.Collections.Generic;
+using System.Drawing;
+using System.Linq;
+using System.Windows.Forms;
+using OpenNest.Controls;
+using OpenNest.Geometry;
+
+namespace OpenNest.Forms;
+
+public partial class SimplifierViewerForm : Form
+{
+    private EntityView entityView;
+    private GeometrySimplifier simplifier;
+    private List<Shape> shapes;
+    private List<ArcCandidate> candidates;
+
+    public event System.Action<List<Entity>> Applied;
+
+    public SimplifierViewerForm()
+    {
+        InitializeComponent();
+    }
+
+    public void LoadShapes(List<Shape> shapes, EntityView view, double tolerance = 0.004)
+    {
+        this.shapes = shapes;
+        this.entityView = view;
+        numTolerance.Value = (decimal)tolerance;
+        simplifier = new GeometrySimplifier { Tolerance = tolerance };
+        RunAnalysis();
+        Show();
+        BringToFront();
+    }
+
+    private void RunAnalysis()
+    {
+        candidates = new List<ArcCandidate>();
+        for (var i = 0; i < shapes.Count; i++)
+        {
+            var shapeCandidates = simplifier.Analyze(shapes[i]);
+            foreach (var c in shapeCandidates)
+                c.ShapeIndex = i;
+
+            var axis = GeometrySimplifier.DetectMirrorAxis(shapes[i]);
+            if (axis.IsValid)
+                simplifier.Symmetrize(shapeCandidates, axis);
+
+            candidates.AddRange(shapeCandidates);
+        }
+        RefreshList();
+    }
+
+    private void RefreshList()
+    {
+        listView.BeginUpdate();
+        listView.Items.Clear();
+
+        foreach (var c in candidates)
+        {
+            var item = new ListViewItem(c.LineCount.ToString());
+            item.Checked = c.IsSelected;
+            item.SubItems.Add(c.FittedArc.Radius.ToString("F3"));
+            item.SubItems.Add(c.MaxDeviation.ToString("F4"));
+            item.SubItems.Add($"{c.BoundingBox.Center.X:F1}, {c.BoundingBox.Center.Y:F1}");
+            item.Tag = c;
+            listView.Items.Add(item);
+        }
+
+        listView.EndUpdate();
+        UpdateCountLabel();
+    }
+
+    private void UpdateCountLabel()
+    {
+        var selected = candidates.Count(c => c.IsSelected);
+        lblCount.Text = $"{selected} of {candidates.Count} selected";
+        btnApply.Enabled = selected > 0;
+    }
+
+    private void OnItemSelected(object sender, ListViewItemSelectionChangedEventArgs e)
+    {
+        if (!e.IsSelected || e.Item.Tag is not ArcCandidate candidate)
+        {
+            entityView?.ClearSimplifierPreview();
+            return;
+        }
+
+        // Highlight the candidate lines in the shape
+        var shape = shapes[candidate.ShapeIndex];
+        var highlightEntities = new List<Entity>();
+        for (var i = candidate.StartIndex; i <= candidate.EndIndex; i++)
+            highlightEntities.Add(shape.Entities[i]);
+
+        entityView.SimplifierHighlight = highlightEntities;
+        entityView.SimplifierPreview = candidate.FittedArc;
+
+        // Build tolerance zone by offsetting each original line both directions
+        var tol = simplifier.Tolerance;
+        var leftEntities = new List<Entity>();
+        var rightEntities = new List<Entity>();
+        foreach (var entity in highlightEntities)
+        {
+            var left = entity.OffsetEntity(tol, OffsetSide.Left);
+            var right = entity.OffsetEntity(tol, OffsetSide.Right);
+            if (left != null) leftEntities.Add(left);
+            if (right != null) rightEntities.Add(right);
+        }
+        entityView.SimplifierToleranceLeft = leftEntities;
+        entityView.SimplifierToleranceRight = rightEntities;
+
+        // Zoom with padding for the tolerance zone
+        var padded = new Box(
+            candidate.BoundingBox.X - tol * 2,
+            candidate.BoundingBox.Y - tol * 2,
+            candidate.BoundingBox.Width + tol * 4,
+            candidate.BoundingBox.Length + tol * 4);
+        entityView.ZoomToArea(padded);
+    }
+
+    private void OnItemChecked(object sender, ItemCheckedEventArgs e)
+    {
+        if (e.Item.Tag is ArcCandidate candidate)
+        {
+            candidate.IsSelected = e.Item.Checked;
+            UpdateCountLabel();
+        }
+    }
+
+    private void OnToleranceChanged(object sender, System.EventArgs e)
+    {
+        if (simplifier == null) return;
+        simplifier.Tolerance = (double)numTolerance.Value;
+        entityView?.ClearSimplifierPreview();
+        RunAnalysis();
+    }
+
+    private void OnApplyClick(object sender, System.EventArgs e)
+    {
+        var byShape = candidates
+            .Where(c => c.IsSelected)
+            .GroupBy(c => c.ShapeIndex)
+            .ToDictionary(g => g.Key, g => g.ToList());
+
+        for (var i = 0; i < shapes.Count; i++)
+        {
+            if (byShape.TryGetValue(i, out var selected))
+                shapes[i] = simplifier.Apply(shapes[i], selected);
+        }
+
+        var entities = shapes.SelectMany(s => s.Entities).ToList();
+        entityView?.ClearSimplifierPreview();
+        Applied?.Invoke(entities);
+        Close();
+    }
+
+    protected override bool ProcessDialogKey(Keys keyData)
+    {
+        if (keyData == Keys.Escape)
+        {
+            Close();
+            return true;
+        }
+        return base.ProcessDialogKey(keyData);
+    }
+
+    protected override void OnFormClosing(FormClosingEventArgs e)
+    {
+        entityView?.ClearSimplifierPreview();
+        base.OnFormClosing(e);
+    }
+}

OpenNest/Forms/SimplifierViewerForm.resx

@@ -0,0 +1,120 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!-- 
+    Microsoft ResX Schema 
+    
+    Version 2.0
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
+    associated with the data types.
+    
+    Example:
+    
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+                
+    There are any number of "resheader" rows that contain simple 
+    name/value pairs.
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
+    mimetype set.
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
+    extensible. For a given mimetype the value must be set accordingly:
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
+    read any of the formats listed below.
+    
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+    
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with 
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array 
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+</root>

OpenNest/Properties/Settings.Designer.cs

@@ -214,5 +214,17 @@ namespace OpenNest.Properties {
                 this["LastPierceTime"] = value;
             }
         }
+
+        [global::System.Configuration.UserScopedSettingAttribute()]
+        [global::System.Diagnostics.DebuggerNonUserCodeAttribute()]
+        [global::System.Configuration.DefaultSettingValueAttribute("")]
+        public string DisabledStrategies {
+            get {
+                return ((string)(this["DisabledStrategies"]));
+            }
+            set {
+                this["DisabledStrategies"] = value;
+            }
+        }
     }
 }

OpenNest/Properties/Settings.settings

@@ -50,5 +50,8 @@
     <Setting Name="LastPierceTime" Type="System.Decimal" Scope="User">
       <Value Profile="(Default)">0</Value>
     </Setting>
+    <Setting Name="DisabledStrategies" Type="System.String" Scope="User">
+      <Value Profile="(Default)" />
+    </Setting>
   </Settings>
 </SettingsFile>

README.md

@@ -1,6 +1,6 @@
 # OpenNest
 
-A Windows desktop app for CNC nesting — imports DXF drawings, arranges parts on plates and exports layouts as DXF or G-code for cutting.
+A Windows desktop application for CNC nesting — imports DXF drawings, arranges parts on material plates, and exports layouts as DXF or G-code for cutting.
 
 ![OpenNest - parts nested on a 36x36 plate](screenshots/screenshot-nest-1.png)
 
@@ -8,15 +8,21 @@ OpenNest takes your part drawings, lets you define your sheet (plate) sizes, and
 
 ## Features
 
-- **DXF Import/Export** — Load part drawings from DXF files and export completed nest layouts
-- **Multiple Fill Strategies** — Grid-based linear fill and rectangle bin packing
-- **Part Rotation** — Automatically tries different rotation angles to find better fits
-- **Gravity Compaction** — After placing parts, pushes them together to close gaps
+- **DXF/DWG Import & Export** — Load part drawings from DXF or DWG files and export completed nest layouts as DXF
+- **Multiple Fill Strategies** — Grid-based linear fill, interlocking pair fill, rectangle bin packing, extents-based tiling, and more via a pluggable strategy system
+- **Best-Fit Pair Nesting** — NFP-based (No Fit Polygon) pair evaluation finds tight-fitting interlocking orientations between parts
+- **GPU Acceleration** — Optional ILGPU-based bitmap overlap detection for faster best-fit evaluation
+- **Part Rotation** — Automatically tries different rotation angles to find better fits, with optional ML-based angle prediction (ONNX)
+- **Gravity Compaction** — After placing parts, pushes them together using polygon-based directional distance to close gaps between irregular shapes
 - **Multi-Plate Support** — Work with multiple plates of different sizes and materials in a single nest
-- **G-code Output** — Post-process nested layouts to G-code for CNC cutting machines
-- **Built-in Shapes** — Create basic geometric parts (circles, rectangles, triangles, etc.) without needing a DXF file
-- **Interactive Editing** — Zoom, pan, select, clone, and manually arrange parts on the plate view
-- **Lead-in/Lead-out & Tabs** — Cutting parameters like approach paths and holding tabs (engine support, UI coming soon)
+- **Sheet Cut-Offs** — Automatically cut the plate to size after nesting, with geometry-aware clearance that avoids placed parts
+- **Drawing Splitting** — Split oversized parts into pieces that fit your plate, with straight cuts, weld-gap tabs, or interlocking spike-groove joints
+- **Bend Line Detection** — Import bend lines from DXF files with pluggable detectors (SolidWorks flat pattern support built in)
+- **Lead-In/Lead-Out & Tabs** — Configurable approach paths, exit paths, and holding tabs for CNC cutting
+- **G-code Output** — Post-process nested layouts to G-code via plugin post-processors
+- **Built-in Shapes** — 12 parametric shapes (circles, rectangles, L-shapes, T-shapes, flanges, etc.) for quick testing or simple parts
+- **Interactive Editing** — Zoom, pan, select, clone, push, and manually arrange parts on the plate view
+- **Pluggable Engine Architecture** — Swap between built-in nesting engines or load custom engines from plugin DLLs
 
 ![OpenNest - 44 parts nested on a 60x120 plate](screenshots/screenshot-nest-2.png)
 
@@ -46,12 +52,11 @@ Or open `OpenNest.sln` in Visual Studio and run the `OpenNest` project.
 ### Quick Walkthrough
 
 1. **Create a nest** — File > New Nest
-2. **Add drawings** — Import DXF files or create built-in shapes (rectangles, circles, etc.). DXF drawings should be 1:1 scale CAD files.
-3. **Set up a plate** — Define the plate size and material
-4. **Fill the plate** — The nesting engine will automatically arrange parts on the plate
-5. **Export** — Save as a `.nest` file, export to DXF, or post-process to G-code
-
-<!-- TODO: Add screenshots for each step -->
+2. **Add drawings** — Import DXF files via the CAD Converter (handles bend detection, layer filtering, and color/linetype exclusion) or create built-in shapes
+3. **Set up a plate** — Define the plate size, material, quadrant, and spacing
+4. **Fill the plate** — The nesting engine arranges parts automatically using the active fill strategy
+5. **Add cut-offs** — Optionally add horizontal/vertical cut-off lines to trim unused plate material
+6. **Export** — Save as a `.nest` file, export to DXF, or post-process to G-code
 
 ## Command-Line Interface
 
@@ -95,6 +100,7 @@ dotnet run --project OpenNest.Console/OpenNest.Console.csproj -- project.zip ext
 | `--keep-parts` | Keep existing parts instead of clearing before fill |
 | `--check-overlaps` | Run overlap detection after fill (exits with code 1 if found) |
 | `--engine <name>` | Select a registered nesting engine |
+| `--post <name>` | Post-process the result with the named post-processor plugin |
 | `--no-save` | Skip saving the output file |
 | `--no-log` | Skip writing the debug log |
 
@@ -102,26 +108,74 @@ dotnet run --project OpenNest.Console/OpenNest.Console.csproj -- project.zip ext
 
 ```
 OpenNest.sln
-├── OpenNest/              # WinForms desktop application (UI)
-├── OpenNest.Core/         # Domain model, geometry, and CNC primitives
-├── OpenNest.Engine/       # Nesting algorithms (fill, pack, compact)
-├── OpenNest.IO/           # File I/O — DXF import/export, nest file format
-├── OpenNest.Console/      # Command-line interface for batch nesting
-├── OpenNest.Gpu/          # GPU-accelerated nesting evaluation
-├── OpenNest.Training/     # ML training data collection
-├── OpenNest.Mcp/          # MCP server for AI tool integration
-└── OpenNest.Tests/        # Unit tests
+├── OpenNest/                   # WinForms desktop application (UI)
+├── OpenNest.Core/              # Domain model, geometry, and CNC primitives
+├── OpenNest.Engine/            # Nesting algorithms (fill, pack, compact, best-fit)
+├── OpenNest.IO/                # File I/O — DXF import/export, nest file format
+├── OpenNest.Console/           # Command-line interface for batch nesting
+├── OpenNest.Api/               # Programmatic nesting API (NestRunner pipeline)
+├── OpenNest.Gpu/               # GPU-accelerated pair evaluation (ILGPU)
+├── OpenNest.Training/          # ML training data collection (SQLite + EF Core)
+├── OpenNest.Mcp/               # MCP server for AI tool integration
+├── OpenNest.Posts.Cincinnati/  # Cincinnati CL-707 laser post-processor plugin
+└── OpenNest.Tests/             # Unit tests (xUnit)
 ```
 
-For most users, only these matter:
-
 | Project | What it does |
 |---------|-------------|
-| **OpenNest** | The app you run. WinForms UI with plate viewer, drawing list, and dialogs. |
+| **OpenNest** | The app you run. WinForms MDI interface with plate viewer, drawing list, CAD converter, and dialogs. |
 | **OpenNest.Console** | Command-line interface for batch nesting, scripting, and automation. |
-| **OpenNest.Core** | The building blocks — parts, plates, drawings, geometry, G-code representation. |
-| **OpenNest.Engine** | The brains — algorithms that decide where parts go on a plate. |
-| **OpenNest.IO** | Reads and writes files — DXF (via ACadSharp), G-code, and the `.nest` ZIP format. |
+| **OpenNest.Core** | The building blocks — parts, plates, drawings, geometry, G-code representation, bend lines, cut-offs, and drawing splitting. |
+| **OpenNest.Engine** | The brains — fill strategies (linear, pairs, rect best-fit, extents), NFP-based pair evaluation, gravity compaction, and a pluggable engine registry. |
+| **OpenNest.IO** | Reads and writes files — DXF/DWG (via ACadSharp), G-code, and the `.nest` ZIP format. |
+| **OpenNest.Api** | High-level API for running the full nesting pipeline programmatically (import, nest, export). |
+| **OpenNest.Gpu** | GPU-accelerated bitmap overlap detection for best-fit pair evaluation using ILGPU. |
+| **OpenNest.Posts.Cincinnati** | Post-processor plugin for Cincinnati CL-707/800/900/940/CLX laser cutting machines. Outputs Cincinnati-format G-code with material library, kerf compensation, and pierce logic. |
+| **OpenNest.Mcp** | MCP (Model Context Protocol) server exposing nesting operations as tools for AI assistants. |
+| **OpenNest.Tests** | 75+ test files covering core geometry, fill strategies, splitting, bending, post-processing, and the API. |
+
+## Nesting Engines
+
+OpenNest uses a pluggable engine architecture. The active engine can be selected at runtime.
+
+| Engine | Description |
+|--------|-------------|
+| **Default** | Multi-phase strategy: linear fill, pair fill, rect best-fit, then remainder. Balances density and speed. |
+| **Vertical Remnant** | Optimizes for a clean vertical drop on the right side of the plate. |
+| **Horizontal Remnant** | Optimizes for a clean horizontal drop on the top of the plate. |
+
+Custom engines can be built by subclassing `NestEngineBase` and registering via `NestEngineRegistry` or dropping a plugin DLL in the `Engines/` directory.
+
+### Fill Strategies
+
+Each engine composes from a set of fill strategies:
+
+| Strategy | Description |
+|----------|-------------|
+| **Linear** | Grid-based fill with geometry-aware copy distance and 4-config rotation/axis optimization |
+| **Pairs** | NFP-based interlocking pair evaluation — finds tight-fitting orientations between two parts |
+| **Rect Best-Fit** | Greedy rectangle bin-packing with horizontal and vertical orientation trials |
+| **Extents** | Extents-based pair tiling for simple rectangular arrangements |
+
+## Drawing Splitting
+
+Oversized parts that don't fit on a single plate can be split into smaller pieces:
+
+- **Straight Split** — Clean cut with no joining features
+- **Weld-Gap Tabs** — Rectangular tab spacers on one side for weld alignment
+- **Spike-Groove** — Interlocking V-shaped spike and groove pairs for self-aligning joints
+
+The split system supports fit-to-plate (auto-calculates split lines) and split-by-count modes, with an interactive UI for adjusting split positions and feature parameters.
+
+## Post-Processors
+
+Post-processors convert nested layouts into machine-specific G-code. They are loaded as plugin DLLs from the `Posts/` directory at runtime.
+
+**Included:**
+
+- **Cincinnati** — Full post-processor for Cincinnati CL-707/800/900/940/CLX laser cutting machines with variable declarations, material library resolution, speed classification, kerf compensation, and optional part sub-programs (M98).
+
+Custom post-processors implement the `IPostProcessor` interface and are auto-discovered from DLLs in the `Posts/` directory.
 
 ## Keyboard Shortcuts
 
@@ -131,6 +185,7 @@ For most users, only these matter:
 | `F` | Zoom to fit the plate view |
 | `Shift` + Mouse Wheel | Rotate parts when a drawing is selected |
 | `Shift` + Left Click | Push the selected group of parts to the bottom-left most point |
+| Middle Mouse Click | Rotate selected parts 90 degrees |
 | `X` | Push selected parts left (negative X) |
 | `Shift+X` | Push selected parts right (positive X) |
 | `Y` | Push selected parts down (negative Y) |
@@ -145,18 +200,26 @@ For most users, only these matter:
 | DXF (AutoCAD Drawing Exchange) | Yes | Yes |
 | DWG (AutoCAD Drawing) | Yes | No |
 | G-code | No | Yes (via post-processors) |
+| `.nest` (ZIP-based project format) | Yes | Yes |
+
+## Nest File Format
+
+Nest files (`.nest`) are ZIP archives containing:
+
+- `nest.json` — JSON metadata: nest info, plate defaults, drawings (with bend data), and plates (with parts and cut-offs)
+- `programs/program-N` — G-code text for each drawing's cut program
+- `bestfits/bestfit-N` — Cached best-fit pair evaluation results (optional)
 
 ## Roadmap
 
-- **NFP-based nesting** — No Fit Polygon algorithms and simulated annealing optimizer exist in the engine but aren't integrated into the UI or engine registry yet
-- **Lead-in/Lead-out UI** — Engine support for lead-ins, lead-outs, and tabs is implemented; needs a UI for configuration
-- **Sheet cut-offs** — Cut the sheet to size after nesting to reduce waste
-- **Post-processors** — Plugin interface (`IPostProcessor`) is in place; need to ship built-in post-processors for common CNC controllers
-- **Shape library UI** — Built-in shape generation code exists; needs a browsable library UI for quick access
+- **NFP-based auto-nesting** — Simulated annealing optimizer and NFP placement exist in the engine but aren't exposed as a selectable engine yet
+- **Geometry simplifier** — Replace consecutive small line segments with fitted arcs to reduce program size and improve nesting performance
+- **Shape library UI** — 12 built-in parametric shapes exist in code; needs a browsable library UI for quick access
+- **Additional post-processors** — Plugin interface is in place; more machine-specific post-processors planned
 
 ## Status
 
-OpenNest is under active development. The core nesting workflows function, but there's plenty of room for improvement in packing efficiency, UI polish, and format support. Contributions and feedback are welcome.
+OpenNest is under active development. The core nesting workflows function end-to-end — from DXF import through filling, splitting, cut-offs, and G-code post-processing. Contributions and feedback are welcome.
 
 ## License
 

docs/superpowers/specs/2026-03-27-direct-arc-conversion-design.md

@@ -0,0 +1,147 @@
+# Direct Arc Conversion for Spline and Ellipse Import
+
+## Problem
+
+During DXF import, splines and ellipses are converted to many small line segments (200 for ellipses, control-point polygons for splines), then optionally reconstructed back to arcs via GeometrySimplifier in the CAD converter. This is wasteful and lossy:
+
+- **Ellipses** are sampled into 200 line segments, discarding the known parametric form.
+- **Splines** connect control points with lines, which is geometrically incorrect for B-splines (control points don't lie on the curve).
+- Reconstructing arcs from approximate line segments is less accurate than fitting arcs to the exact curve.
+
+## Solution
+
+Convert splines and ellipses directly to circular arcs (and lines where necessary) during import, using the exact curve geometry. No user review step — the import produces the best representation automatically.
+
+## Design Decisions
+
+| Decision | Choice | Rationale |
+|----------|--------|-----------|
+| When to convert | During import (automatic) | User didn't ask for 200 lines; produce best representation |
+| Tolerance | 0.001" default | Tighter than simplifier's 0.004" because we have exact curves |
+| Ellipse method | Analytical (curvature-based) | We have the exact parametric form |
+| Spline method | Sample-then-fit | ACadSharp provides `PolygonalVertexes()` for accurate curve points |
+| Fallback | Keep line segments where arcs can't fit | Handles rapid curvature changes in splines |
+| Junction continuity | G1 (tangent) continuity | Normal-constrained arc centers prevent serrated edges |
+
+## Architecture
+
+Two new classes in `OpenNest.Core/Geometry/`:
+
+### EllipseConverter
+
+**Input:** Ellipse parameters — center, semi-major axis length, semi-minor axis length, rotation angle, start parameter, end parameter, tolerance.
+
+**Output:** `List<Entity>` containing arcs that approximate the ellipse within tolerance.
+
+**Algorithm — normal-constrained arc fitting:**
+
+1. Compute an initial set of split parameters along the ellipse. Start with quadrant boundaries (points of maximum/minimum curvature) as natural split candidates.
+2. For each pair of consecutive split points (t_start, t_end):
+   a. Compute the ellipse normal at both endpoints analytically.
+   b. Find the arc center at the intersection of the two normals. This guarantees the arc is tangent to the ellipse at both endpoints (G1 continuity).
+   c. Compute the arc radius from the center to either endpoint.
+   d. Sample several points on the ellipse between t_start and t_end, and measure the maximum radial deviation from the fitted arc.
+   e. If deviation exceeds tolerance, subdivide: insert a split point at the midpoint and retry both halves.
+   f. If deviation is within tolerance, emit the arc.
+3. Continue until all segments are within tolerance.
+
+**Ellipse analytical formulas (in local coordinates before rotation):**
+
+- Point: `P(t) = (a cos t, b sin t)`
+- Tangent: `T(t) = (-a sin t, b cos t)`
+- Normal (inward): perpendicular to tangent, pointing toward center of curvature
+- Curvature: `k(t) = ab / (a^2 sin^2 t + b^2 cos^2 t)^(3/2)`
+
+After computing in local coordinates, rotate by the ellipse's major axis angle and translate to center.
+
+**Arc count:** Depends on eccentricity and tolerance. A nearly-circular ellipse needs 1-2 arcs. A highly eccentric one (ratio < 0.3) may need 8-16. Tolerance drives this automatically via subdivision.
+
+**Closed ellipse handling:** When the ellipse sweep is approximately 2pi, ensure the last arc's endpoint connects back to the first arc's start point. Tangent continuity wraps around.
+
+### SplineConverter
+
+**Input:** List of points evaluated on the spline curve (from ACadSharp's `PolygonalVertexes`), tolerance, and whether the spline is closed.
+
+**Output:** `List<Entity>` containing arcs and lines that approximate the spline within tolerance.
+
+**Algorithm — tangent-chained greedy arc fitting:**
+
+1. Evaluate the spline at high density using `PolygonalVertexes(precision)` where precision comes from the existing `SplinePrecision` setting.
+2. Walk the evaluated points from the start:
+   a. At the current segment start, compute the tangent direction from the first two points (or from the chained tangent of the previous arc).
+   b. Fit an arc constrained to be tangent at the start point:
+      - The arc center lies on the normal to the tangent at the start point.
+      - Use the perpendicular bisector of the chord from start to candidate end point, intersected with the start normal, to find the center.
+   c. Extend the arc forward point-by-point. At each extension, recompute the center (intersection of start normal and chord bisector to the new endpoint) and check that all intermediate points are within tolerance of the arc.
+   d. When adding the next point would exceed tolerance, finalize the arc with the last good endpoint.
+   e. Compute the tangent at the arc's end point (perpendicular to the radius at that point) and chain it to the next segment.
+3. If fewer than 3 points remain in a run where no arc fits (curvature changes too rapidly), emit line segments instead.
+4. For closed splines, chain the final arc's tangent back to constrain the first arc.
+
+**This is essentially the same approach GeometrySimplifier uses** (tangent chaining via `chainedTangent`), but operating on densely-sampled curve points rather than pre-existing line segments.
+
+### Changes to Existing Code
+
+#### Extensions.cs
+
+```
+// Before: returns List<Line>
+public static List<Geometry.Line> ToOpenNest(this Spline spline)
+
+// After: returns List<Entity>
+public static List<Entity> ToOpenNest(this Spline spline, int precision)
+```
+
+- Extracts ACadSharp spline data, calls `SplineConverter.Convert()`
+- Now accepts `precision` parameter (was ignored before)
+
+```
+// Before: returns List<Line>
+public static List<Geometry.Line> ToOpenNest(this Ellipse ellipse, int precision = 200)
+
+// After: returns List<Entity>
+public static List<Entity> ToOpenNest(this Ellipse ellipse, double tolerance = 0.001)
+```
+
+- Extracts ACadSharp ellipse parameters, calls `EllipseConverter.Convert()`
+- Precision parameter replaced by tolerance (precision is no longer relevant)
+
+Both methods preserve Layer, Color, and LineTypeName on the output entities.
+
+#### DxfImporter.cs
+
+Currently collects `List<Line>` and `List<Arc>` separately. The new converters return `List<Entity>` (mixed arcs and lines). Options:
+
+- Sort returned entities into the existing `lines` and `arcs` lists by type, OR
+- Switch to a single `List<Entity>` collection
+
+The simpler change is to sort into existing lists so downstream code (GeometryOptimizer, ShapeBuilder) is unaffected.
+
+### What Stays the Same
+
+- **GeometrySimplifier** — still exists for user-triggered simplification of genuinely line-based geometry (e.g., DXF files that actually contain line segments, or polylines)
+- **GeometryOptimizer** — still merges collinear lines and coradial arcs post-import. May merge adjacent arcs produced by the new converters if they happen to be coradial.
+- **ShapeBuilder, ConvertGeometry, CNC pipeline** — unchanged, they already handle mixed Line/Arc entities
+- **SplinePrecision setting** — still used for spline point evaluation density
+
+## Testing
+
+- **EllipseConverter unit tests:**
+  - Circle (ratio = 1.0) produces 1-2 arcs
+  - Moderate ellipse produces arcs within tolerance
+  - Highly eccentric ellipse produces more arcs, all within tolerance
+  - Partial ellipse (elliptical arc) works correctly
+  - Endpoint continuity: each arc's end matches the next arc's start
+  - Tangent continuity: no discontinuities at junctions
+  - Closed ellipse: last arc connects back to first
+
+- **SplineConverter unit tests:**
+  - Circular arc spline produces a single arc
+  - S-curve spline produces arcs + lines where needed
+  - Straight-line spline produces a line (not degenerate arcs)
+  - Closed spline: endpoints connect
+  - Tangent chaining: smooth transitions between consecutive arcs
+
+- **Integration test:**
+  - Import a DXF with splines and ellipses, verify the result contains arcs (not 200 lines)
+  - Compare bounding boxes to ensure geometry is preserved