fix(io): deduplicate circles and full-circle arcs during DXF import

Duplicate circle entities at the same location inflated pierce counts
and cut pricing (e.g. SULLYS-035 showed 9 pierces instead of 8).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

OpenNest.Console/Program.cs

@@ -151,7 +151,8 @@ static class NestConsole
             f.EndsWith(NestFormat.FileExtension, StringComparison.OrdinalIgnoreCase)
             || f.EndsWith(".zip", StringComparison.OrdinalIgnoreCase));
         var dxfFiles = options.InputFiles.Where(f =>
-            f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)).ToList();
+            f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase) ||
+            f.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase)).ToList();
 
         // If we have a nest file, load it and optionally add DXFs.
         if (nestFile != null)
@@ -187,7 +188,7 @@ static class NestConsole
         // DXF-only mode: create a fresh nest.
         if (dxfFiles.Count == 0)
         {
-            Console.Error.WriteLine("Error: no nest (.nest) or DXF (.dxf) files specified");
+            Console.Error.WriteLine("Error: no nest (.nest) or CAD (.dxf/.dwg) files specified");
             return null;
         }
 
@@ -461,7 +462,7 @@ static class NestConsole
         Console.Error.WriteLine("Usage: OpenNest.Console <input-files...> [options]");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Arguments:");
-        Console.Error.WriteLine("  input-files            One or more .nest nest files or .dxf drawing files");
+        Console.Error.WriteLine("  input-files            One or more .nest nest files or .dxf/.dwg drawing files");
         Console.Error.WriteLine();
         Console.Error.WriteLine("Modes:");
         Console.Error.WriteLine("  <nest.nest>             Load nest and fill (existing behavior)");

OpenNest.Core/Converters/ConvertGeometry.cs

@@ -1,5 +1,6 @@
 using OpenNest.CNC;
 using OpenNest.Geometry;
+using OpenNest.Math;
 using System.Collections.Generic;
 
 namespace OpenNest.Converters
@@ -81,12 +82,21 @@ namespace OpenNest.Converters
             var startpt = arc.StartPoint();
             var endpt = arc.EndPoint();
 
-            if (startpt != lastpt)
+            if (startpt.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(startpt);
 
             lastpt = endpt;
 
-            pgm.ArcTo(endpt, arc.Center, arc.IsReversed ? RotationType.CW : RotationType.CCW);
+            var sweep = System.Math.Abs(arc.SweepAngle());
+            if (sweep < Tolerance.Epsilon || sweep.IsEqualTo(Angle.TwoPI))
+            {
+                pgm.LineTo(endpt);
+            }
+            else
+            {
+                pgm.ArcTo(endpt, arc.Center, arc.IsReversed ? RotationType.CW : RotationType.CCW);
+            }
+
             return lastpt;
         }
 
@@ -94,7 +104,7 @@ namespace OpenNest.Converters
         {
             var startpt = new Vector(circle.Center.X + circle.Radius, circle.Center.Y);
 
-            if (startpt != lastpt)
+            if (startpt.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(startpt);
 
             pgm.ArcTo(startpt, circle.Center, circle.Rotation);
@@ -105,7 +115,7 @@ namespace OpenNest.Converters
 
         private static Vector AddLine(Program pgm, Vector lastpt, Line line)
         {
-            if (line.StartPoint != lastpt)
+            if (line.StartPoint.DistanceTo(lastpt) > Tolerance.ChainTolerance)
                 pgm.MoveTo(line.StartPoint);
 
             var move = new LinearMove(line.EndPoint);

OpenNest.Core/Geometry/Arc.cs

@@ -93,6 +93,9 @@ namespace OpenNest.Geometry
             }
         }
 
+        public bool IsFullCircle() =>
+            SweepAngle() >= Angle.TwoPI - Tolerance.Epsilon;
+
         /// <summary>
         /// Angle in radians between start and end angles.
         /// </summary>

OpenNest.Core/Geometry/Box.cs

@@ -1,8 +1,9 @@
-using OpenNest.Math;
+using System;
+using OpenNest.Math;
 
 namespace OpenNest.Geometry
 {
-    public class Box
+    public class Box : IComparable<Box>
     {
         public static readonly Box Empty = new Box();
 
@@ -214,5 +215,19 @@ namespace OpenNest.Geometry
         {
             return string.Format("[Box: X={0}, Y={1}, Width={2}, Length={3}]", X, Y, Width, Length);
         }
+
+        public int CompareTo(Box other)
+        {
+            var cmp = Width.CompareTo(other.Width);
+            return cmp != 0 ? cmp : Length.CompareTo(other.Length);
+        }
+
+        public static bool operator >(Box a, Box b) => a.CompareTo(b) > 0;
+
+        public static bool operator <(Box a, Box b) => a.CompareTo(b) < 0;
+
+        public static bool operator >=(Box a, Box b) => a.CompareTo(b) >= 0;
+
+        public static bool operator <=(Box a, Box b) => a.CompareTo(b) <= 0;
     }
 }

OpenNest.Core/Geometry/EllipseConverter.cs

@@ -173,7 +173,11 @@ namespace OpenNest.Geometry
 
             if (maxDev <= tolerance)
             {
-                results.Add(CreateArc(arcCenter, radius, center, semiMajor, semiMinor, rotation, t0, t1));
+                var arc = CreateArc(arcCenter, radius, center, semiMajor, semiMinor, rotation, t0, t1);
+                if (arc.SweepAngle() < Tolerance.Epsilon)
+                    results.Add(new Line(p0, p1));
+                else
+                    results.Add(arc);
             }
             else
             {

OpenNest.Core/Geometry/GeometryOptimizer.cs

@@ -17,6 +17,38 @@ namespace OpenNest.Geometry
                 (list, item, i) => list.GetCollinearLines(item, i),
                 (Line a, Line b, out Line joined) => TryJoinLines(a, b, out joined));
 
+        public static void Deduplicate(IList<Circle> circles)
+        {
+            for (var i = circles.Count - 1; i >= 1; i--)
+            {
+                for (var j = i - 1; j >= 0; j--)
+                {
+                    if (circles[i].Center.DistanceTo(circles[j].Center) <= Tolerance.Epsilon
+                        && circles[i].Radius.IsEqualTo(circles[j].Radius))
+                    {
+                        circles.RemoveAt(i);
+                        break;
+                    }
+                }
+            }
+        }
+
+        public static void Deduplicate(IList<Circle> circles, IList<Arc> arcs)
+        {
+            for (var i = circles.Count - 1; i >= 0; i--)
+            {
+                for (var j = arcs.Count - 1; j >= 0; j--)
+                {
+                    if (arcs[j].Center.DistanceTo(circles[i].Center) <= Tolerance.Epsilon
+                        && arcs[j].Radius.IsEqualTo(circles[i].Radius)
+                        && arcs[j].IsFullCircle())
+                    {
+                        arcs.RemoveAt(j);
+                    }
+                }
+            }
+        }
+
         private delegate bool TryJoin<T>(T a, T b, out T joined);
 
         private static void MergePass<T>(IList<T> items,

OpenNest.Core/Geometry/ShapeBuilder.cs

@@ -1,12 +1,13 @@
 using OpenNest.Math;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Linq;
 
 namespace OpenNest.Geometry
 {
     public static class ShapeBuilder
     {
-        public static List<Shape> GetShapes(IEnumerable<Entity> entities)
+        public static List<Shape> GetShapes(IEnumerable<Entity> entities, double? weldTolerance = null)
         {
             var lines = new List<Line>();
             var arcs = new List<Arc>();
@@ -57,6 +58,9 @@ namespace OpenNest.Geometry
             entityList.AddRange(lines);
             entityList.AddRange(arcs);
 
+            if (weldTolerance.HasValue)
+                WeldEndpoints(entityList, weldTolerance.Value);
+
             while (entityList.Count > 0)
             {
                 var next = entityList[0];
@@ -107,6 +111,93 @@ namespace OpenNest.Geometry
             return shapes;
         }
 
+        public static void WeldEndpoints(List<Entity> entities, double tolerance)
+        {
+            var endpointGroups = new List<List<(Entity entity, bool isStart, Vector point)>>();
+
+            foreach (var entity in entities)
+            {
+                var (start, end) = GetEndpoints(entity);
+                if (!start.IsValid() || !end.IsValid())
+                    continue;
+
+                AddToGroup(endpointGroups, entity, true, start, tolerance);
+                AddToGroup(endpointGroups, entity, false, end, tolerance);
+            }
+
+            foreach (var group in endpointGroups)
+            {
+                if (group.Count <= 1)
+                    continue;
+
+                var avgX = group.Average(g => g.point.X);
+                var avgY = group.Average(g => g.point.Y);
+                var weldedPoint = new Vector(avgX, avgY);
+
+                foreach (var (entity, isStart, _) in group)
+                    ApplyWeld(entity, isStart, weldedPoint);
+            }
+        }
+
+        private static void AddToGroup(
+            List<List<(Entity entity, bool isStart, Vector point)>> groups,
+            Entity entity, bool isStart, Vector point, double tolerance)
+        {
+            foreach (var group in groups)
+            {
+                if (group[0].point.DistanceTo(point) <= tolerance)
+                {
+                    group.Add((entity, isStart, point));
+                    return;
+                }
+            }
+
+            groups.Add(new List<(Entity, bool, Vector)> { (entity, isStart, point) });
+        }
+
+        private static (Vector start, Vector end) GetEndpoints(Entity entity)
+        {
+            switch (entity.Type)
+            {
+                case EntityType.Arc:
+                    var arc = (Arc)entity;
+                    return (arc.StartPoint(), arc.EndPoint());
+
+                case EntityType.Line:
+                    var line = (Line)entity;
+                    return (line.StartPoint, line.EndPoint);
+
+                default:
+                    return (Vector.Invalid, Vector.Invalid);
+            }
+        }
+
+        private static void ApplyWeld(Entity entity, bool isStart, Vector weldedPoint)
+        {
+            switch (entity.Type)
+            {
+                case EntityType.Line:
+                    var line = (Line)entity;
+                    if (isStart)
+                        line.StartPoint = weldedPoint;
+                    else
+                        line.EndPoint = weldedPoint;
+                    break;
+
+                case EntityType.Arc:
+                    var arc = (Arc)entity;
+                    var deltaX = weldedPoint.X - arc.Center.X;
+                    var deltaY = weldedPoint.Y - arc.Center.Y;
+                    var angle = System.Math.Atan2(deltaY, deltaX);
+
+                    if (isStart)
+                        arc.StartAngle = angle;
+                    else
+                        arc.EndAngle = angle;
+                    break;
+            }
+        }
+
         internal static Entity GetConnected(Vector pt, IEnumerable<Entity> geometry)
         {
             var tol = Tolerance.ChainTolerance;

OpenNest.Core/Math/Fraction.cs

@@ -3,7 +3,7 @@ using System.Linq;
 using System.Text;
 using System.Text.RegularExpressions;
 
-namespace OpenNest.IO.Bom
+namespace OpenNest.Math
 {
     public static class Fraction
     {

OpenNest.IO/Bom/BomAnalyzer.cs

@@ -42,6 +42,11 @@ namespace OpenNest.IO.Bom
                     var nameWithoutExt = Path.GetFileNameWithoutExtension(file);
                     dxfFiles[nameWithoutExt] = file;
                 }
+                foreach (var file in Directory.GetFiles(dxfFolder, "*.dwg"))
+                {
+                    var nameWithoutExt = Path.GetFileNameWithoutExtension(file);
+                    dxfFiles.TryAdd(nameWithoutExt, file);
+                }
             }
 
             // Partition items into: skipped, unmatched, or matched (grouped)
@@ -57,8 +62,8 @@ namespace OpenNest.IO.Bom
 
                 var lookupName = item.FileName;
 
-                // Strip .dxf extension if the BOM includes it
-                if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase))
+                if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)
+                    || lookupName.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase))
                     lookupName = Path.GetFileNameWithoutExtension(lookupName);
 
                 if (!folderExists)

OpenNest.IO/CadImportOptions.cs

@@ -16,6 +16,11 @@ namespace OpenNest.IO
         /// </summary>
         public bool DetectBends { get; set; } = true;
 
+        /// <summary>
+        /// When true, detects and identifies title block entities during import. Default true.
+        /// </summary>
+        public bool DetectTitleBlock { get; set; } = true;
+
         /// <summary>
         /// Override the drawing name. Null = filename without extension.
         /// </summary>

OpenNest.IO/CadImportResult.cs

@@ -1,4 +1,5 @@
 using System.Collections.Generic;
+using ACadSharp;
 using OpenNest.Bending;
 using OpenNest.Geometry;
 
@@ -38,5 +39,16 @@ namespace OpenNest.IO
         /// Default drawing name (filename without extension, unless overridden).
         /// </summary>
         public string Name { get; set; }
+
+        /// <summary>
+        /// The raw CAD document from the source file. Available for callers
+        /// that need access to non-geometry entities (e.g., text annotations).
+        /// </summary>
+        public CadDocument Document { get; set; }
+
+        /// <summary>
+        /// GUIDs of entities identified as part of the title block during import.
+        /// </summary>
+        public HashSet<System.Guid> TitleBlockEntityIds { get; set; }
     }
 }

OpenNest.IO/CadImporter.cs

@@ -5,6 +5,7 @@ using OpenNest.Bending;
 using OpenNest.Converters;
 using OpenNest.Geometry;
 using OpenNest.IO.Bending;
+using OpenNest.Math;
 
 namespace OpenNest.IO
 {
@@ -25,6 +26,9 @@ namespace OpenNest.IO
 
             var dxf = Dxf.Import(path);
 
+            RemoveDuplicateArcs(dxf.Entities);
+            RemoveZeroSweepArcs(dxf.Entities);
+
             var bends = new List<Bend>();
             if (options.DetectBends && dxf.Document != null)
             {
@@ -37,6 +41,10 @@ namespace OpenNest.IO
 
             Bend.UpdateEtchEntities(dxf.Entities, bends);
 
+            HashSet<System.Guid> titleBlockIds = null;
+            if (options.DetectTitleBlock)
+                titleBlockIds = TitleBlockDetector.Detect(dxf.Entities, dxf.Document);
+
             return new CadImportResult
             {
                 Entities = dxf.Entities,
@@ -44,6 +52,8 @@ namespace OpenNest.IO
                 Bounds = dxf.Entities.GetBoundingBox(),
                 SourcePath = path,
                 Name = options.Name ?? Path.GetFileNameWithoutExtension(path),
+                Document = dxf.Document,
+                TitleBlockEntityIds = titleBlockIds,
             };
         }
 
@@ -134,7 +144,51 @@ namespace OpenNest.IO
                     .Where(e => !(e.Layer != null && e.Layer.IsVisible && e.IsVisible))
                     .Select(e => e.Id));
 
+            if (result.TitleBlockEntityIds != null)
+            {
+                var sourceIds = new HashSet<System.Guid>(drawing.SourceEntities.Select(e => e.Id));
+                foreach (var id in result.TitleBlockEntityIds)
+                {
+                    if (sourceIds.Contains(id))
+                        drawing.SuppressedEntityIds.Add(id);
+                }
+            }
+
             return drawing;
         }
+
+        internal static void RemoveZeroSweepArcs(List<Entity> entities)
+        {
+            entities.RemoveAll(e =>
+                e is Arc arc && arc.StartAngle.IsEqualTo(arc.EndAngle, Tolerance.ChainTolerance));
+        }
+
+        internal static void RemoveDuplicateArcs(List<Entity> entities)
+        {
+            var circles = entities.OfType<Circle>().ToList();
+            var arcs = entities.OfType<Arc>().ToList();
+            var arcsToRemove = new List<Arc>();
+
+            foreach (var arc in arcs)
+            {
+                foreach (var circle in circles)
+                {
+                    if (arc.Layer?.Name != circle.Layer?.Name)
+                        continue;
+
+                    if (!arc.Center.DistanceTo(circle.Center).IsEqualTo(0))
+                        continue;
+
+                    if (!arc.Radius.IsEqualTo(circle.Radius))
+                        continue;
+
+                    arcsToRemove.Add(arc);
+                    break;
+                }
+            }
+
+            foreach (var arc in arcsToRemove)
+                entities.Remove(arc);
+        }
     }
 }

OpenNest.IO/Dxf.cs

@@ -27,8 +27,7 @@ namespace OpenNest.IO
         /// </summary>
         public static DxfImportResult Import(string path)
         {
-            using var reader = new DxfReader(path);
-            var doc = reader.Read();
+            var doc = ReadDocument(path);
 
             return new DxfImportResult
             {
@@ -41,8 +40,7 @@ namespace OpenNest.IO
         {
             try
             {
-                using var reader = new DxfReader(path);
-                var doc = reader.Read();
+                var doc = ReadDocument(path);
                 return ConvertEntities(doc);
             }
             catch (Exception ex)
@@ -113,11 +111,29 @@ namespace OpenNest.IO
 
         #region Private
 
+        private static bool IsDwg(string path) =>
+            Path.GetExtension(path).Equals(".dwg", StringComparison.OrdinalIgnoreCase);
+
+        private static CadDocument ReadDocument(string path)
+        {
+            if (IsDwg(path))
+            {
+                using var reader = new DwgReader(path);
+                return reader.Read();
+            }
+            else
+            {
+                using var reader = new DxfReader(path);
+                return reader.Read();
+            }
+        }
+
         private static List<Entity> ConvertEntities(CadDocument doc)
         {
             var entities = new List<Entity>();
             var lines = new List<Line>();
             var arcs = new List<Arc>();
+            var circles = new List<Circle>();
 
             foreach (var entity in doc.Entities)
             {
@@ -135,7 +151,7 @@ namespace OpenNest.IO
                         break;
 
                     case ACadSharp.Entities.Circle circle:
-                        entities.Add(circle.ToOpenNest());
+                        circles.Add(circle.ToOpenNest());
                         break;
 
                     case ACadSharp.Entities.Spline spline:
@@ -166,7 +182,10 @@ namespace OpenNest.IO
 
             GeometryOptimizer.Optimize(lines);
             GeometryOptimizer.Optimize(arcs);
+            GeometryOptimizer.Deduplicate(circles);
+            GeometryOptimizer.Deduplicate(circles, arcs);
 
+            entities.AddRange(circles);
             entities.AddRange(lines);
             entities.AddRange(arcs);
 

OpenNest.IO/TitleBlockDetector.cs

@@ -0,0 +1,312 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using ACadSharp;
+using OpenNest.Geometry;
+
+namespace OpenNest.IO
+{
+    public static class TitleBlockDetector
+    {
+        private static readonly HashSet<string> TitleBlockLayerNames = new(StringComparer.OrdinalIgnoreCase)
+        {
+            "TITLE", "TITLEBLOCK", "TITLE_BLOCK", "BORDER", "FRAME",
+            "TB", "INFO", "SHEET", "ANNOTATION"
+        };
+
+        public static HashSet<Guid> Detect(List<Entity> entities, CadDocument document)
+        {
+            var flagged = new HashSet<Guid>();
+            DetectByLayerName(entities, flagged);
+            DetectBorder(entities, flagged);
+            if (document != null)
+                DetectTitleBlockRegion(entities, document, flagged);
+            return flagged;
+        }
+
+        private static void DetectByLayerName(List<Entity> entities, HashSet<Guid> flagged)
+        {
+            foreach (var entity in entities)
+            {
+                if (entity.Layer?.Name != null && TitleBlockLayerNames.Contains(entity.Layer.Name))
+                    flagged.Add(entity.Id);
+            }
+        }
+
+        private static void DetectBorder(List<Entity> entities, HashSet<Guid> flagged)
+        {
+            var lines = entities.OfType<Line>().Where(l => !flagged.Contains(l.Id)).ToList();
+            if (lines.Count < 4) return;
+
+            var bounds = entities.GetBoundingBox();
+            if (bounds == null || bounds.Area() < OpenNest.Math.Tolerance.Epsilon) return;
+
+            var borderCount = 0;
+            foreach (var line in lines)
+            {
+                if (IsBorderLine(line, bounds))
+                {
+                    flagged.Add(line.Id);
+                    borderCount++;
+                }
+            }
+
+            if (borderCount >= 2)
+                DetectZoneMarkers(lines, bounds, flagged);
+        }
+
+        private static bool IsBorderLine(Line line, Box bounds)
+        {
+            var dx = line.EndPoint.X - line.StartPoint.X;
+            var dy = line.EndPoint.Y - line.StartPoint.Y;
+            var length = System.Math.Sqrt(dx * dx + dy * dy);
+            var angleRad = System.Math.Atan2(System.Math.Abs(dy), System.Math.Abs(dx));
+            var angularTolerance = OpenNest.Math.Angle.ToRadians(2.0);
+            var positionTolerance = System.Math.Max(bounds.Length, bounds.Width) * 0.01;
+
+            var isHorizontal = angleRad < angularTolerance;
+            var isVertical = System.Math.Abs(angleRad - System.Math.PI / 2) < angularTolerance;
+
+            if (!isHorizontal && !isVertical) return false;
+
+            var minSpan = isHorizontal ? bounds.Length * 0.8 : bounds.Width * 0.8;
+            if (length < minSpan) return false;
+
+            if (isHorizontal)
+            {
+                var midY = (line.StartPoint.Y + line.EndPoint.Y) / 2;
+                return System.Math.Abs(midY - bounds.Bottom) < positionTolerance
+                    || System.Math.Abs(midY - bounds.Top) < positionTolerance;
+            }
+            else
+            {
+                var midX = (line.StartPoint.X + line.EndPoint.X) / 2;
+                return System.Math.Abs(midX - bounds.Left) < positionTolerance
+                    || System.Math.Abs(midX - bounds.Right) < positionTolerance;
+            }
+        }
+
+        private static void DetectZoneMarkers(List<Line> lines, Box bounds, HashSet<Guid> flagged)
+        {
+            var positionTolerance = System.Math.Max(bounds.Length, bounds.Width) * 0.01;
+            var maxTickLength = System.Math.Max(bounds.Length, bounds.Width) * 0.05;
+            var angularTolerance = OpenNest.Math.Angle.ToRadians(2.0);
+
+            foreach (var line in lines)
+            {
+                if (flagged.Contains(line.Id)) continue;
+
+                var dx = line.EndPoint.X - line.StartPoint.X;
+                var dy = line.EndPoint.Y - line.StartPoint.Y;
+                var length = System.Math.Sqrt(dx * dx + dy * dy);
+
+                if (length > maxTickLength || length < OpenNest.Math.Tolerance.Epsilon) continue;
+
+                var angleRad = System.Math.Atan2(System.Math.Abs(dy), System.Math.Abs(dx));
+                var isVertical = System.Math.Abs(angleRad - System.Math.PI / 2) < angularTolerance;
+                var isHorizontal = angleRad < angularTolerance;
+
+                if (!isVertical && !isHorizontal) continue;
+
+                var touchesEdge = false;
+                if (isVertical)
+                {
+                    var minY = System.Math.Min(line.StartPoint.Y, line.EndPoint.Y);
+                    var maxY = System.Math.Max(line.StartPoint.Y, line.EndPoint.Y);
+                    touchesEdge = System.Math.Abs(minY - bounds.Bottom) < positionTolerance
+                               || System.Math.Abs(maxY - bounds.Top) < positionTolerance;
+                }
+                else if (isHorizontal)
+                {
+                    var minX = System.Math.Min(line.StartPoint.X, line.EndPoint.X);
+                    var maxX = System.Math.Max(line.StartPoint.X, line.EndPoint.X);
+                    touchesEdge = System.Math.Abs(minX - bounds.Left) < positionTolerance
+                               || System.Math.Abs(maxX - bounds.Right) < positionTolerance;
+                }
+
+                if (touchesEdge)
+                    flagged.Add(line.Id);
+            }
+        }
+
+        private static void DetectTitleBlockRegion(List<Entity> entities, CadDocument document, HashSet<Guid> flagged)
+        {
+            var textPositions = ExtractTextPositions(document);
+            if (textPositions.Count < 3) return;
+
+            var unflagged = entities.Where(e => !flagged.Contains(e.Id)).ToList();
+            if (unflagged.Count == 0) return;
+
+            var bounds = entities.GetBoundingBox();
+            if (bounds == null || bounds.Area() < OpenNest.Math.Tolerance.Epsilon) return;
+
+            var bestRegion = FindBestTitleBlockRegion(bounds, textPositions, unflagged);
+            if (bestRegion == null) return;
+
+            var initiallyInside = unflagged.Where(e => {
+                var c = EntityCenter(e);
+                return c.HasValue && RegionContains(bestRegion, c.Value);
+            }).ToList();
+
+            var expandedBounds = initiallyInside.Count > 0 ? initiallyInside.GetBoundingBox() : null;
+
+            foreach (var entity in unflagged)
+            {
+                var center = EntityCenter(entity);
+                if (!center.HasValue) continue;
+                if (RegionContains(bestRegion, center.Value)
+                    || (expandedBounds != null && RegionContains(expandedBounds, center.Value)))
+                    flagged.Add(entity.Id);
+            }
+        }
+
+        private static List<Vector> ExtractTextPositions(CadDocument document)
+        {
+            var positions = new List<Vector>();
+            foreach (var entity in document.Entities)
+            {
+                switch (entity)
+                {
+                    case ACadSharp.Entities.MText mtext:
+                        positions.Add(new Vector(mtext.InsertPoint.X, mtext.InsertPoint.Y));
+                        break;
+                    case ACadSharp.Entities.TextEntity text:
+                        var pt = text.HorizontalAlignment != 0 || text.VerticalAlignment != 0
+                            ? text.AlignmentPoint : text.InsertPoint;
+                        positions.Add(new Vector(pt.X, pt.Y));
+                        break;
+                }
+            }
+            return positions;
+        }
+
+        private static Box FindBestTitleBlockRegion(Box bounds, List<Vector> textPositions, List<Entity> entities)
+        {
+            var candidates = GenerateCandidateRegions(bounds);
+            Box bestRegion = null;
+            var bestScore = 0.0;
+
+            var openLines = FindOpenLines(entities);
+
+            foreach (var region in candidates)
+            {
+                var textCount = textPositions.Count(p => RegionContains(region, p));
+                if (textCount < 3) continue;
+
+                var openLineCount = openLines.Count(l => RegionContains(region, l.MidPoint));
+
+                var area = region.Area();
+                if (area < OpenNest.Math.Tolerance.Epsilon) continue;
+
+                var score = (double)textCount + openLineCount * 0.5;
+
+                var regionCenterX = (region.Left + region.Right) / 2;
+                var regionCenterY = (region.Bottom + region.Top) / 2;
+                if (regionCenterX > bounds.Center.X) score *= 1.3;
+                if (regionCenterY < bounds.Center.Y) score *= 1.3;
+
+                if (score > bestScore)
+                {
+                    bestScore = score;
+                    bestRegion = region;
+                }
+            }
+
+            return bestRegion;
+        }
+
+        private static List<Box> GenerateCandidateRegions(Box bounds)
+        {
+            var regions = new List<Box>();
+            var fractions = new[] { 0.25, 0.333, 0.5 };
+
+            foreach (var fx in fractions)
+            {
+                foreach (var fy in fractions)
+                {
+                    var w = bounds.Length * fx;
+                    var h = bounds.Width * fy;
+
+                    regions.Add(new Box(bounds.Right - w, bounds.Bottom, w, h));
+                    regions.Add(new Box(bounds.Left, bounds.Bottom, w, h));
+                    regions.Add(new Box(bounds.Right - w, bounds.Top - h, w, h));
+                    regions.Add(new Box(bounds.Left, bounds.Top - h, w, h));
+                }
+            }
+
+            foreach (var fy in fractions)
+            {
+                var h = bounds.Width * fy;
+                regions.Add(new Box(bounds.Left, bounds.Bottom, bounds.Length, h));
+            }
+
+            foreach (var fx in fractions)
+            {
+                var w = bounds.Length * fx;
+                regions.Add(new Box(bounds.Right - w, bounds.Bottom, w, bounds.Width));
+            }
+
+            return regions;
+        }
+
+        private static List<Line> FindOpenLines(List<Entity> entities)
+        {
+            var endpointUsers = new Dictionary<long, int>();
+
+            foreach (var entity in entities)
+            {
+                foreach (var ep in GetEntityEndpoints(entity))
+                {
+                    var key = QuantizePoint(ep);
+                    endpointUsers[key] = endpointUsers.GetValueOrDefault(key) + 1;
+                }
+            }
+
+            var openLines = new List<Line>();
+            foreach (var line in entities.OfType<Line>())
+            {
+                var startKey = QuantizePoint(line.StartPoint);
+                var endKey = QuantizePoint(line.EndPoint);
+
+                if (endpointUsers.GetValueOrDefault(startKey) <= 1 || endpointUsers.GetValueOrDefault(endKey) <= 1)
+                    openLines.Add(line);
+            }
+
+            return openLines;
+        }
+
+        private static List<Vector> GetEntityEndpoints(Entity entity)
+        {
+            return entity switch
+            {
+                Line line => new List<Vector> { line.StartPoint, line.EndPoint },
+                Arc arc => new List<Vector> { arc.StartPoint(), arc.EndPoint() },
+                _ => new List<Vector>()
+            };
+        }
+
+        private static long QuantizePoint(Vector pt)
+        {
+            var qx = (long)(pt.X * 1000);
+            var qy = (long)(pt.Y * 1000);
+            return qx * 100000000L + qy;
+        }
+
+        private static Vector? EntityCenter(Entity entity)
+        {
+            return entity switch
+            {
+                Line line => line.MidPoint,
+                Arc arc => arc.Center,
+                Circle circle => circle.Center,
+                _ => null
+            };
+        }
+
+        private static bool RegionContains(Box box, Vector pt)
+        {
+            return pt.X >= box.Left && pt.X <= box.Right
+                && pt.Y >= box.Bottom && pt.Y <= box.Top;
+        }
+    }
+}

OpenNest.Tests/Engine/NestInvarianceTests.cs

@@ -0,0 +1,84 @@
+using OpenNest.CNC;
+using OpenNest.Engine;
+using OpenNest.Engine.BestFit;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using System.Threading;
+
+namespace OpenNest.Tests.Engine;
+
+public class NestInvarianceTests
+{
+    private static OpenNest.CNC.Program MakeLShapedProgram()
+    {
+        // L-shape: 100x50 outer rect with a 50x30 notch removed from top-right.
+        var pgm = new OpenNest.CNC.Program();
+        pgm.Codes.Add(new RapidMove(new Vector(0, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(100, 0)));
+        pgm.Codes.Add(new LinearMove(new Vector(100, 20)));
+        pgm.Codes.Add(new LinearMove(new Vector(50, 20)));
+        pgm.Codes.Add(new LinearMove(new Vector(50, 50)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 50)));
+        pgm.Codes.Add(new LinearMove(new Vector(0, 0)));
+        return pgm;
+    }
+
+    private static Drawing MakeImportedAt(double rotation)
+    {
+        var pgm = MakeLShapedProgram();
+        if (!Tolerance.IsEqualTo(rotation, 0))
+            pgm.Rotate(rotation, pgm.BoundingBox().Center);
+        return new Drawing("L", pgm);
+    }
+
+    private static Plate MakePlate() => new Plate(new Size(500, 500))
+    {
+        Quadrant = 1,
+        PartSpacing = 2,
+    };
+
+    private static int RunFillCount(Drawing drawing, Plate plate)
+    {
+        BestFitCache.Clear();
+        var engine = new DefaultNestEngine(plate);
+        var item = new NestItem { Drawing = drawing };
+        var parts = engine.Fill(item, plate.WorkArea(), progress: null, token: CancellationToken.None);
+        return parts?.Count ?? 0;
+    }
+
+    [Theory]
+    [InlineData(0.0)]
+    [InlineData(0.3)]
+    [InlineData(0.8)]
+    [InlineData(1.2)]
+    public void Fill_SameCount_AcrossImportOrientations(double theta)
+    {
+        var baseline = RunFillCount(MakeImportedAt(0.0), MakePlate());
+        var rotated = RunFillCount(MakeImportedAt(theta), MakePlate());
+
+        // Allow +/-1 tolerance for sweep quantization edge effects near plate boundaries.
+        Assert.InRange(rotated, baseline - 1, baseline + 1);
+    }
+
+    [Fact]
+    public void Fill_PlacedPartsStayWithinWorkArea_AcrossImportOrientations()
+    {
+        var plate = MakePlate();
+        var workArea = plate.WorkArea();
+
+        foreach (var theta in new[] { 0.0, 0.3, 0.8, 1.2 })
+        {
+            BestFitCache.Clear();
+            var engine = new DefaultNestEngine(plate);
+            var item = new NestItem { Drawing = MakeImportedAt(theta) };
+            var parts = engine.Fill(item, workArea, progress: null, token: CancellationToken.None);
+
+            Assert.NotNull(parts);
+            foreach (var p in parts)
+            {
+                Assert.InRange(p.BoundingBox.Left, workArea.Left - 0.5, workArea.Right + 0.5);
+                Assert.InRange(p.BoundingBox.Bottom, workArea.Bottom - 0.5, workArea.Top + 0.5);
+            }
+        }
+    }
+}

OpenNest.Tests/Geometry/BoxComparisonTests.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+using OpenNest.Geometry;
+using Xunit;
+
+namespace OpenNest.Tests.Geometry;
+
+public class BoxComparisonTests
+{
+    [Fact]
+    public void GreaterThan_TallerBox_ReturnsTrue()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(tall > short_);
+        Assert.False(short_ > tall);
+    }
+
+    [Fact]
+    public void GreaterThan_SameWidthLongerBox_ReturnsTrue()
+    {
+        var longer = new Box(0, 0, 20, 10);
+        var shorter = new Box(0, 0, 10, 10);
+
+        Assert.True(longer > shorter);
+        Assert.False(shorter > longer);
+    }
+
+    [Fact]
+    public void LessThan_ShorterBox_ReturnsTrue()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(short_ < tall);
+        Assert.False(tall < short_);
+    }
+
+    [Fact]
+    public void GreaterThanOrEqual_EqualBoxes_ReturnsTrue()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.True(a >= b);
+        Assert.True(b >= a);
+    }
+
+    [Fact]
+    public void LessThanOrEqual_EqualBoxes_ReturnsTrue()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.True(a <= b);
+        Assert.True(b <= a);
+    }
+
+    [Fact]
+    public void CompareTo_TallerBox_ReturnsPositive()
+    {
+        var tall = new Box(0, 0, 10, 20);
+        var short_ = new Box(0, 0, 10, 10);
+
+        Assert.True(tall.CompareTo(short_) > 0);
+        Assert.True(short_.CompareTo(tall) < 0);
+    }
+
+    [Fact]
+    public void CompareTo_EqualBoxes_ReturnsZero()
+    {
+        var a = new Box(0, 0, 10, 20);
+        var b = new Box(0, 0, 10, 20);
+
+        Assert.Equal(0, a.CompareTo(b));
+    }
+
+    [Fact]
+    public void Sort_OrdersByWidthThenLength()
+    {
+        var boxes = new List<Box>
+        {
+            new Box(0, 0, 20, 10),
+            new Box(0, 0, 5, 30),
+            new Box(0, 0, 10, 10),
+        };
+
+        boxes.Sort();
+
+        Assert.Equal(10, boxes[0].Width);
+        Assert.Equal(10, boxes[0].Length);
+        Assert.Equal(10, boxes[1].Width);
+        Assert.Equal(20, boxes[1].Length);
+        Assert.Equal(30, boxes[2].Width);
+    }
+}

OpenNest.Tests/Geometry/WeldEndpointsTests.cs

@@ -0,0 +1,72 @@
+using System.Collections.Generic;
+using OpenNest.Geometry;
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.Geometry;
+
+public class WeldEndpointsTests
+{
+    [Fact]
+    public void WeldEndpoints_SnapsNearbyLineEndpoints()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.0000005, 0, 20, 0);
+        var entities = new List<Entity> { line1, line2 };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.000001);
+
+        Assert.True(line1.EndPoint.DistanceTo(line2.StartPoint) <= Tolerance.Epsilon);
+    }
+
+    [Fact]
+    public void WeldEndpoints_SnapsArcEndpointByAdjustingAngle()
+    {
+        var line = new Line(0, 0, 10, 0);
+        var arc = new Arc(15, 0, 5, Angle.ToRadians(180.001), Angle.ToRadians(90));
+        var entities = new List<Entity> { line, arc };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.01);
+
+        var arcStart = arc.StartPoint();
+        Assert.True(line.EndPoint.DistanceTo(arcStart) <= 0.01);
+    }
+
+    [Fact]
+    public void WeldEndpoints_DoesNotWeldDistantEndpoints()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.1, 0, 20, 0);
+        var entities = new List<Entity> { line1, line2 };
+
+        ShapeBuilder.WeldEndpoints(entities, 0.000001);
+
+        Assert.True(line1.EndPoint.DistanceTo(line2.StartPoint) > 0.01);
+    }
+
+    [Fact]
+    public void GetShapes_WithWeldTolerance_WeldsBeforeChaining()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10.0000005, 0, 10.0000005, 10);
+        var entities = new List<Entity> { line1, line2 };
+
+        var shapes = ShapeBuilder.GetShapes(entities, weldTolerance: 0.000001);
+
+        Assert.Single(shapes);
+        Assert.Equal(2, shapes[0].Entities.Count);
+    }
+
+    [Fact]
+    public void GetShapes_WithoutWeldTolerance_DefaultBehavior()
+    {
+        var line1 = new Line(0, 0, 10, 0);
+        var line2 = new Line(10, 0, 10, 10);
+        var entities = new List<Entity> { line1, line2 };
+
+        var shapes = ShapeBuilder.GetShapes(entities);
+
+        Assert.Single(shapes);
+        Assert.Equal(2, shapes[0].Entities.Count);
+    }
+}

OpenNest.Tests/IO/CadImporterTests.cs

@@ -134,5 +134,21 @@ namespace OpenNest.Tests.IO
             Assert.NotNull(drawing.Program);
             Assert.NotNull(drawing.SourceEntities);
         }
+
+        [Fact]
+        public void Import_WhenDetectTitleBlockTrue_PopulatesTitleBlockEntityIds()
+        {
+            var result = CadImporter.Import(TestDxf);
+
+            Assert.NotNull(result.TitleBlockEntityIds);
+        }
+
+        [Fact]
+        public void Import_WhenDetectTitleBlockFalse_TitleBlockEntityIdsIsNull()
+        {
+            var result = CadImporter.Import(TestDxf, new CadImportOptions { DetectTitleBlock = false });
+
+            Assert.Null(result.TitleBlockEntityIds);
+        }
     }
 }

OpenNest.Tests/IO/RemoveDuplicateArcsTests.cs

@@ -0,0 +1,96 @@
+using System.Collections.Generic;
+using System.Linq;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.IO;
+
+public class RemoveDuplicateArcsTests
+{
+    [Fact]
+    public void RemoveDuplicateArcs_RemovesArcMatchingCircle_SameLayer()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var line = new Line(0, 0, 10, 0) { Layer = layer };
+        var entities = new List<Entity> { circle, arc, line };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+        Assert.Contains(circle, entities);
+        Assert.Contains(line, entities);
+        Assert.DoesNotContain(arc, entities);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcOnDifferentLayer()
+    {
+        var layer1 = new Layer("cut");
+        var layer2 = new Layer("etch");
+        var circle = new Circle(10, 10, 5) { Layer = layer1 };
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer2 };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+        Assert.Contains(arc, entities);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcWithDifferentRadius()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(10, 10, 3, 0, Angle.ToRadians(90)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_KeepsArcWithDifferentCenter()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc = new Arc(20, 20, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_NoCircles_NoChange()
+    {
+        var arc = new Arc(10, 10, 5, 0, Angle.ToRadians(90));
+        var line = new Line(0, 0, 10, 0);
+        var entities = new List<Entity> { arc, line };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Equal(2, entities.Count);
+    }
+
+    [Fact]
+    public void RemoveDuplicateArcs_MultipleArcsMatchOneCircle_RemovesAll()
+    {
+        var layer = new Layer("0");
+        var circle = new Circle(10, 10, 5) { Layer = layer };
+        var arc1 = new Arc(10, 10, 5, 0, Angle.ToRadians(90)) { Layer = layer };
+        var arc2 = new Arc(10, 10, 5, Angle.ToRadians(90), Angle.ToRadians(180)) { Layer = layer };
+        var entities = new List<Entity> { circle, arc1, arc2 };
+
+        CadImporter.RemoveDuplicateArcs(entities);
+
+        Assert.Single(entities);
+        Assert.Contains(circle, entities);
+    }
+}

OpenNest.Tests/IO/TitleBlockDetectorTests.cs

@@ -0,0 +1,245 @@
+using System.Collections.Generic;
+using CSMath;
+using OpenNest.Geometry;
+using OpenNest.IO;
+using Xunit;
+
+namespace OpenNest.Tests.IO
+{
+    public class TitleBlockDetectorTests
+    {
+        private static Line MakeLine(double x1, double y1, double x2, double y2) =>
+            new Line(x1, y1, x2, y2);
+
+        [Fact]
+        public void DetectByLayerName_FlagsTitleLayer()
+        {
+            var line = MakeLine(0, 0, 10, 0);
+            line.Layer = new Layer("TITLE");
+            var entities = new List<Entity> { line };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(line.Id, result);
+        }
+
+        [Fact]
+        public void DetectByLayerName_CaseInsensitive()
+        {
+            var line = MakeLine(0, 0, 10, 0);
+            line.Layer = new Layer("border");
+            var entities = new List<Entity> { line };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(line.Id, result);
+        }
+
+        [Fact]
+        public void DetectByLayerName_IgnoresNonMatchingLayers()
+        {
+            var line = MakeLine(0, 0, 10, 0);
+            line.Layer = new Layer("0");
+            var entities = new List<Entity> { line };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.DoesNotContain(line.Id, result);
+        }
+
+        [Theory]
+        [InlineData("TITLE")]
+        [InlineData("TITLEBLOCK")]
+        [InlineData("TITLE_BLOCK")]
+        [InlineData("BORDER")]
+        [InlineData("FRAME")]
+        [InlineData("TB")]
+        [InlineData("INFO")]
+        [InlineData("SHEET")]
+        [InlineData("ANNOTATION")]
+        public void DetectByLayerName_AllKnownNames(string layerName)
+        {
+            var line = MakeLine(0, 0, 10, 0);
+            line.Layer = new Layer(layerName);
+            var entities = new List<Entity> { line };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(line.Id, result);
+        }
+
+        [Fact]
+        public void DetectBorder_FlagsLinesOnBoundingBoxEdges()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(0, 0, 86, 0) { Layer = new Layer("0") },
+                new Line(86, 0, 86, 134) { Layer = new Layer("0") },
+                new Line(86, 134, 0, 134) { Layer = new Layer("0") },
+                new Line(0, 134, 0, 0) { Layer = new Layer("0") },
+                new Line(30, 40, 50, 90) { Layer = new Layer("0") },
+                new Line(50, 90, 70, 40) { Layer = new Layer("0") },
+                new Line(70, 40, 30, 40) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(entities[0].Id, result);
+            Assert.Contains(entities[1].Id, result);
+            Assert.Contains(entities[2].Id, result);
+            Assert.Contains(entities[3].Id, result);
+            Assert.DoesNotContain(entities[4].Id, result);
+            Assert.DoesNotContain(entities[5].Id, result);
+            Assert.DoesNotContain(entities[6].Id, result);
+        }
+
+        [Fact]
+        public void DetectBorder_FlagsZoneMarkerTicks()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(0, 0, 100, 0) { Layer = new Layer("0") },
+                new Line(100, 0, 100, 80) { Layer = new Layer("0") },
+                new Line(100, 80, 0, 80) { Layer = new Layer("0") },
+                new Line(0, 80, 0, 0) { Layer = new Layer("0") },
+                new Line(25, 80, 25, 77) { Layer = new Layer("0") },
+                new Line(50, 80, 50, 77) { Layer = new Layer("0") },
+                new Line(75, 80, 75, 77) { Layer = new Layer("0") },
+                new Line(40, 30, 60, 30) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(entities[4].Id, result);
+            Assert.Contains(entities[5].Id, result);
+            Assert.Contains(entities[6].Id, result);
+            Assert.DoesNotContain(entities[7].Id, result);
+        }
+
+        [Fact]
+        public void DetectBorder_IgnoresWhenNoBorderPresent()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(30, 40, 50, 90) { Layer = new Layer("0") },
+                new Line(50, 90, 70, 40) { Layer = new Layer("0") },
+                new Line(70, 40, 30, 40) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Empty(result);
+        }
+
+        [Fact]
+        public void DetectBorder_ToleratesSlightRotation()
+        {
+            var angleRad = OpenNest.Math.Angle.ToRadians(0.5);
+            var endY = 86 * System.Math.Sin(angleRad);
+            var entities = new List<Entity>
+            {
+                new Line(0, 0, 86, endY) { Layer = new Layer("0") },
+                new Line(86, endY, 86, 134) { Layer = new Layer("0") },
+                new Line(86, 134, 0, 134) { Layer = new Layer("0") },
+                new Line(0, 134, 0, 0) { Layer = new Layer("0") },
+                new Line(30, 40, 50, 90) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Contains(entities[0].Id, result);
+        }
+
+        [Fact]
+        public void DetectTitleBlock_FlagsEntitiesInTextDenseCorner()
+        {
+            var partLine1 = new Line(5, 70, 25, 120) { Layer = new Layer("0") };
+            var partLine2 = new Line(25, 120, 45, 70) { Layer = new Layer("0") };
+            var partLine3 = new Line(45, 70, 5, 70) { Layer = new Layer("0") };
+
+            var tbLines = new List<Entity>();
+            for (var x = 50; x <= 85; x += 5)
+                tbLines.Add(new Line(x, 0, x, 30) { Layer = new Layer("0") });
+            for (var y = 0; y <= 30; y += 5)
+                tbLines.Add(new Line(50, y, 85, y) { Layer = new Layer("0") });
+
+            var entities = new List<Entity> { partLine1, partLine2, partLine3 };
+            entities.AddRange(tbLines);
+
+            var doc = BuildDocWithTexts(
+                (60, 5, "TITLE: Test Part"),
+                (60, 10, "DWG NO: 12345"),
+                (60, 15, "SCALE: 1:1"),
+                (60, 20, "REV: A"),
+                (60, 25, "MATERIAL: STEEL"));
+
+            var result = TitleBlockDetector.Detect(entities, doc);
+
+            foreach (var tb in tbLines)
+                Assert.Contains(tb.Id, result);
+            Assert.DoesNotContain(partLine1.Id, result);
+            Assert.DoesNotContain(partLine2.Id, result);
+            Assert.DoesNotContain(partLine3.Id, result);
+        }
+
+        [Fact]
+        public void DetectTitleBlock_NoFalsePositivesWithoutText()
+        {
+            var entities = new List<Entity>
+            {
+                new Line(30, 40, 50, 90) { Layer = new Layer("0") },
+                new Line(50, 90, 70, 40) { Layer = new Layer("0") },
+                new Line(70, 40, 30, 40) { Layer = new Layer("0") },
+            };
+
+            var result = TitleBlockDetector.Detect(entities, null);
+
+            Assert.Empty(result);
+        }
+
+        [Fact]
+        public void DetectTitleBlock_BottomEdgeStrip()
+        {
+            var partLine = new Line(20, 40, 80, 40) { Layer = new Layer("0") };
+
+            var tbLines = new List<Entity>();
+            for (var x = 0; x <= 100; x += 10)
+                tbLines.Add(new Line(x, 0, x, 20) { Layer = new Layer("0") });
+            for (var y = 0; y <= 20; y += 5)
+                tbLines.Add(new Line(0, y, 100, y) { Layer = new Layer("0") });
+
+            var entities = new List<Entity> { partLine };
+            entities.AddRange(tbLines);
+
+            var doc = BuildDocWithTexts(
+                (10, 5, "TITLE"),
+                (30, 5, "DWG NO"),
+                (50, 5, "SCALE"),
+                (70, 5, "REV"),
+                (90, 5, "DATE"));
+
+            var result = TitleBlockDetector.Detect(entities, doc);
+
+            foreach (var tb in tbLines)
+                Assert.Contains(tb.Id, result);
+            Assert.DoesNotContain(partLine.Id, result);
+        }
+
+        private static ACadSharp.CadDocument BuildDocWithTexts(
+            params (double x, double y, string value)[] texts)
+        {
+            var doc = new ACadSharp.CadDocument();
+            foreach (var (x, y, value) in texts)
+            {
+                var mtext = new ACadSharp.Entities.MText
+                {
+                    InsertPoint = new XYZ(x, y, 0),
+                    Value = value,
+                    Height = 2.0
+                };
+                doc.Entities.Add(mtext);
+            }
+            return doc;
+        }
+    }
+}

OpenNest.Tests/Math/FractionTests.cs

@@ -0,0 +1,46 @@
+using OpenNest.Math;
+using Xunit;
+
+namespace OpenNest.Tests.Math;
+
+public class FractionTests
+{
+    [Theory]
+    [InlineData("3/8", 0.375)]
+    [InlineData("1 3/4", 1.75)]
+    [InlineData("1-3/4", 1.75)]
+    [InlineData("1/2", 0.5)]
+    public void Parse_ValidFraction_ReturnsDouble(string input, double expected)
+    {
+        var result = Fraction.Parse(input);
+
+        Assert.Equal(expected, result, 8);
+    }
+
+    [Theory]
+    [InlineData("3/8", true)]
+    [InlineData("abc", false)]
+    [InlineData("1 3/4", true)]
+    public void IsValid_ReturnsExpected(string input, bool expected)
+    {
+        Assert.Equal(expected, Fraction.IsValid(input));
+    }
+
+    [Fact]
+    public void TryParse_InvalidInput_ReturnsFalse()
+    {
+        var result = Fraction.TryParse("abc", out var value);
+
+        Assert.False(result);
+        Assert.Equal(0, value);
+    }
+
+    [Fact]
+    public void ReplaceFractionsWithDecimals_ReplacesFractionInString()
+    {
+        var result = Fraction.ReplaceFractionsWithDecimals("length is 1 3/4 inches");
+
+        Assert.Contains("1.75", result);
+        Assert.DoesNotContain("3/4", result);
+    }
+}

OpenNest.Training/Program.cs

@@ -89,8 +89,10 @@ int RunDataCollection(string dir, string dbPath, string saveDir, double s, strin
         new Size(48, 24), new Size(120, 10)
     };
 
-    var dxfFiles = Directory.GetFiles(dir, "*.dxf", SearchOption.AllDirectories);
-    Console.WriteLine($"Found {dxfFiles.Length} DXF files");
+    var dxfFiles = Directory.GetFiles(dir, "*.dxf", SearchOption.AllDirectories)
+        .Concat(Directory.GetFiles(dir, "*.dwg", SearchOption.AllDirectories))
+        .ToArray();
+    Console.WriteLine($"Found {dxfFiles.Length} CAD files");
     var resolvedDb = dbPath.EndsWith(".db", StringComparison.OrdinalIgnoreCase) ? dbPath : dbPath + ".db";
     Console.WriteLine($"Database: {Path.GetFullPath(resolvedDb)}");
     Console.WriteLine($"Sheet sizes: {sheetSuite.Length} configurations");

OpenNest/Actions/ActionCutOff.cs

@@ -16,15 +16,11 @@ namespace OpenNest.Actions
         private CutOffSettings settings;
         private CutOffAxis lockedAxis = CutOffAxis.Vertical;
         private Dictionary<Part, Entity> perimeterCache;
-        private readonly Timer debounceTimer;
-        private bool regeneratePending;
 
         public ActionCutOff(PlateView plateView)
             : base(plateView)
         {
             settings = plateView.CutOffSettings;
-            debounceTimer = new Timer { Interval = 16 };
-            debounceTimer.Tick += OnDebounce;
             ConnectEvents();
         }
 
@@ -40,8 +36,6 @@ namespace OpenNest.Actions
 
         public override void DisconnectEvents()
         {
-            debounceTimer.Stop();
-            debounceTimer.Dispose();
             plateView.MouseMove -= OnMouseMove;
             plateView.MouseDown -= OnMouseDown;
             plateView.KeyDown -= OnKeyDown;
@@ -58,18 +52,6 @@ namespace OpenNest.Actions
 
         private void OnMouseMove(object sender, MouseEventArgs e)
         {
-            regeneratePending = true;
-            debounceTimer.Start();
-        }
-
-        private void OnDebounce(object sender, System.EventArgs e)
-        {
-            debounceTimer.Stop();
-
-            if (!regeneratePending)
-                return;
-
-            regeneratePending = false;
             var pt = plateView.CurrentPoint;
             previewCutOff = new CutOff(pt, lockedAxis);
             previewCutOff.Regenerate(plateView.Plate, settings, perimeterCache);

OpenNest/ArchUnits.cs

@@ -1,4 +1,4 @@
-using OpenNest.IO.Bom;
+using OpenNest.Math;
 using System;
 using System.Drawing;
 using System.Text;

OpenNest/Controls/CadText.cs

@@ -0,0 +1,16 @@
+using System.Drawing;
+using OpenNest.Geometry;
+
+namespace OpenNest.Controls
+{
+    public class CadText
+    {
+        public Vector Position { get; set; }
+        public string Value { get; set; }
+        public double Height { get; set; }
+        public double Rotation { get; set; }
+        public string LayerName { get; set; }
+        public StringAlignment HAlign { get; set; }
+        public StringAlignment VAlign { get; set; }
+    }
+}

OpenNest/Controls/EntityView.cs

@@ -29,12 +29,17 @@ namespace OpenNest.Controls
         public List<Entity> SimplifierToleranceRight { get; set; }
         public List<Entity> OriginalEntities { get; set; }
         public bool ShowEntityLabels { get; set; }
+        public List<CadText> Texts { get; set; } = new List<CadText>();
+        public HashSet<Guid> TitleBlockEntityIds { get; set; }
 
         private readonly Pen gridPen = new Pen(Color.FromArgb(70, 70, 70));
         private readonly Dictionary<int, Pen> penCache = new Dictionary<int, Pen>();
+        private readonly Dictionary<int, Pen> ghostPenCache = new Dictionary<int, Pen>();
         private readonly Font labelFont = new Font("Segoe UI", 7f);
         private readonly SolidBrush labelBrush = new SolidBrush(Color.FromArgb(220, 255, 255, 200));
         private readonly SolidBrush labelBackBrush = new SolidBrush(Color.FromArgb(33, 40, 48));
+        private readonly SolidBrush textBrush = new SolidBrush(Color.FromArgb(180, 200, 200, 200));
+        private readonly SolidBrush ghostTextBrush = new SolidBrush(Color.FromArgb(50, 200, 200, 200));
 
         public event EventHandler<Line> LinePicked;
         public event EventHandler PickCancelled;
@@ -100,6 +105,13 @@ namespace OpenNest.Controls
             foreach (var entity in Entities)
             {
                 if (IsEtchLayer(entity.Layer)) continue;
+
+                if (TitleBlockEntityIds != null && TitleBlockEntityIds.Contains(entity.Id))
+                {
+                    DrawGhostEntity(e.Graphics, entity);
+                    continue;
+                }
+
                 var isHighlighted = simplifierHighlightSet != null && simplifierHighlightSet.Contains(entity);
                 var pen = isHighlighted
                     ? GetEntityPen(Color.FromArgb(60, entity.Color))
@@ -116,6 +128,8 @@ namespace OpenNest.Controls
                 DrawEntity(e.Graphics, entity, pen);
             }
 
+            DrawTexts(e.Graphics);
+
             if (ShowEntityLabels)
                 DrawEntityLabels(e.Graphics);
 
@@ -239,11 +253,26 @@ namespace OpenNest.Controls
             return pen;
         }
 
+        private Pen GetGhostPen(Color color)
+        {
+            var ghostColor = Color.FromArgb(60, color.R, color.G, color.B);
+            var argb = ghostColor.ToArgb();
+            if (!ghostPenCache.TryGetValue(argb, out var pen))
+            {
+                pen = new Pen(ghostColor);
+                ghostPenCache[argb] = pen;
+            }
+            return pen;
+        }
+
         public void ClearPenCache()
         {
             foreach (var pen in penCache.Values)
                 pen.Dispose();
             penCache.Clear();
+            foreach (var pen in ghostPenCache.Values)
+                pen.Dispose();
+            ghostPenCache.Clear();
         }
 
         private static bool IsEtchLayer(Layer layer) =>
@@ -408,10 +437,29 @@ namespace OpenNest.Controls
                 labelFont.Dispose();
                 labelBrush.Dispose();
                 labelBackBrush.Dispose();
+                textBrush.Dispose();
+                ghostTextBrush.Dispose();
             }
             base.Dispose(disposing);
         }
 
+        private void DrawGhostEntity(Graphics g, Entity e)
+        {
+            var pen = GetGhostPen(e.Color);
+            switch (e.Type)
+            {
+                case EntityType.Arc:
+                    DrawArc(g, (Arc)e, pen);
+                    break;
+                case EntityType.Circle:
+                    DrawCircle(g, (Circle)e, pen);
+                    break;
+                case EntityType.Line:
+                    DrawLine(g, (Line)e, pen);
+                    break;
+            }
+        }
+
         private void DrawEntity(Graphics g, Entity e, Pen pen)
         {
             if (!e.Layer.IsVisible || !e.IsVisible)
@@ -474,6 +522,36 @@ namespace OpenNest.Controls
                 diameter);
         }
 
+        private void DrawTexts(Graphics g)
+        {
+            if (Texts == null || Texts.Count == 0)
+                return;
+
+            using var sf = new StringFormat();
+
+            foreach (var text in Texts)
+            {
+                var pos = PointWorldToGraph(text.Position);
+                var fontSize = LengthWorldToGui(text.Height);
+                if (fontSize < 2f) continue;
+
+                var state = g.Save();
+                g.TranslateTransform(pos.X, pos.Y);
+
+                if (text.Rotation != 0)
+                    g.RotateTransform((float)OpenNest.Math.Angle.ToDegrees(text.Rotation));
+
+                sf.Alignment = text.HAlign;
+                sf.LineAlignment = text.VAlign;
+
+                var brush = TitleBlockEntityIds != null && TitleBlockEntityIds.Count > 0
+                    ? ghostTextBrush : textBrush;
+                using var font = new Font("Segoe UI", fontSize, GraphicsUnit.Pixel);
+                g.DrawString(text.Value, font, brush, 0, 0, sf);
+                g.Restore(state);
+            }
+        }
+
         private void DrawPoint(Graphics g, Vector pt, Pen pen)
         {
             var pt1 = PointWorldToGraph(pt);

OpenNest/Controls/FileListControl.cs

@@ -20,8 +20,10 @@ namespace OpenNest.Controls
         public List<Entity> OriginalEntities { get; set; }
         public List<Bend> Bends { get; set; } = new();
         public HashSet<Guid> SuppressedEntityIds { get; set; }
+        public HashSet<Guid> TitleBlockEntityIds { get; set; }
         public Box Bounds { get; set; }
         public int EntityCount { get; set; }
+        public List<CadText> Texts { get; set; } = new();
     }
 
     public class FileListControl : Control

OpenNest/Forms/BomImportForm.cs

@@ -165,7 +165,8 @@ namespace OpenNest.Forms
                 else
                 {
                     var lookupName = item.FileName;
-                    if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase))
+                    if (lookupName.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)
+                        || lookupName.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase))
                         lookupName = Path.GetFileNameWithoutExtension(lookupName);
 
                     if (matchedPaths.TryGetValue(lookupName, out var dxfPath))

OpenNest/Forms/CadConverterForm.cs

@@ -92,9 +92,18 @@ namespace OpenNest.Forms
                     Customer = string.Empty,
                     Bends = result.Bends,
                     Bounds = result.Bounds,
-                    EntityCount = result.Entities.Count
+                    EntityCount = result.Entities.Count,
+                    Texts = ExtractTexts(result.Document),
+                    TitleBlockEntityIds = result.TitleBlockEntityIds,
                 };
 
+                if (result.TitleBlockEntityIds != null && result.TitleBlockEntityIds.Count > 0)
+                {
+                    item.SuppressedEntityIds ??= new HashSet<Guid>();
+                    foreach (var id in result.TitleBlockEntityIds)
+                        item.SuppressedEntityIds.Add(id);
+                }
+
                 if (InvokeRequired)
                     BeginInvoke((Action)(() => fileList.AddItem(item)));
                 else
@@ -152,6 +161,8 @@ namespace OpenNest.Forms
             entityView1.Entities.Clear();
             entityView1.Entities.AddRange(item.Entities);
             entityView1.Bends = item.Bends ?? new List<Bend>();
+            entityView1.Texts = item.Texts ?? new List<CadText>();
+            entityView1.TitleBlockEntityIds = item.TitleBlockEntityIds;
 
             item.Entities.ForEach(e => e.IsVisible = true);
             if (item.Entities.Any(e => e.Layer != null))
@@ -473,7 +484,8 @@ namespace OpenNest.Forms
             {
                 var files = (string[])e.Data.GetData(DataFormats.FileDrop);
                 var dxfFiles = files.Where(f =>
-                    f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase)).ToArray();
+                    f.EndsWith(".dxf", StringComparison.OrdinalIgnoreCase) ||
+                    f.EndsWith(".dwg", StringComparison.OrdinalIgnoreCase)).ToArray();
                 if (dxfFiles.Length > 0)
                     AddFiles(dxfFiles);
             }
@@ -803,6 +815,102 @@ namespace OpenNest.Forms
 
         #endregion
 
+        private static List<CadText> ExtractTexts(ACadSharp.CadDocument doc)
+        {
+            var texts = new List<CadText>();
+            if (doc == null) return texts;
+
+            foreach (var entity in doc.Entities)
+            {
+                switch (entity)
+                {
+                    case ACadSharp.Entities.MText mtext:
+                        var (mh, mv) = MapAttachmentPoint(mtext.AttachmentPoint);
+                        texts.Add(new CadText
+                        {
+                            Position = new Vector(mtext.InsertPoint.X, mtext.InsertPoint.Y),
+                            Value = ReplaceControlCodes(StripMTextFormatting(mtext.Value)),
+                            Height = mtext.Height,
+                            Rotation = mtext.Rotation,
+                            LayerName = mtext.Layer?.Name,
+                            HAlign = mh,
+                            VAlign = mv,
+                        });
+                        break;
+
+                    case ACadSharp.Entities.TextEntity text:
+                        var useAlignment = text.HorizontalAlignment != 0
+                            || text.VerticalAlignment != 0;
+                        var pt = useAlignment ? text.AlignmentPoint : text.InsertPoint;
+                        var ha = text.HorizontalAlignment switch
+                        {
+                            ACadSharp.Entities.TextHorizontalAlignment.Center => System.Drawing.StringAlignment.Center,
+                            ACadSharp.Entities.TextHorizontalAlignment.Right => System.Drawing.StringAlignment.Far,
+                            _ => System.Drawing.StringAlignment.Near,
+                        };
+                        texts.Add(new CadText
+                        {
+                            Position = new Vector(pt.X, pt.Y),
+                            Value = ReplaceControlCodes(text.Value),
+                            Height = text.Height,
+                            Rotation = text.Rotation,
+                            LayerName = text.Layer?.Name,
+                            HAlign = ha,
+                        });
+                        break;
+                }
+            }
+
+            return texts;
+        }
+
+        private static (System.Drawing.StringAlignment h, System.Drawing.StringAlignment v) MapAttachmentPoint(
+            ACadSharp.Entities.AttachmentPointType apt)
+        {
+            var h = apt switch
+            {
+                ACadSharp.Entities.AttachmentPointType.TopCenter
+                    or ACadSharp.Entities.AttachmentPointType.MiddleCenter
+                    or ACadSharp.Entities.AttachmentPointType.BottomCenter => System.Drawing.StringAlignment.Center,
+                ACadSharp.Entities.AttachmentPointType.TopRight
+                    or ACadSharp.Entities.AttachmentPointType.MiddleRight
+                    or ACadSharp.Entities.AttachmentPointType.BottomRight => System.Drawing.StringAlignment.Far,
+                _ => System.Drawing.StringAlignment.Near,
+            };
+            var v = apt switch
+            {
+                ACadSharp.Entities.AttachmentPointType.MiddleLeft
+                    or ACadSharp.Entities.AttachmentPointType.MiddleCenter
+                    or ACadSharp.Entities.AttachmentPointType.MiddleRight => System.Drawing.StringAlignment.Center,
+                ACadSharp.Entities.AttachmentPointType.BottomLeft
+                    or ACadSharp.Entities.AttachmentPointType.BottomCenter
+                    or ACadSharp.Entities.AttachmentPointType.BottomRight => System.Drawing.StringAlignment.Far,
+                _ => System.Drawing.StringAlignment.Near,
+            };
+            return (h, v);
+        }
+
+        private static string StripMTextFormatting(string text)
+        {
+            if (string.IsNullOrEmpty(text)) return text;
+            var result = System.Text.RegularExpressions.Regex.Replace(text, @"\\[A-Za-z][^;]*;", "");
+            result = result.Replace("{", "").Replace("}", "");
+            return result.Trim();
+        }
+
+        private static string ReplaceControlCodes(string text)
+        {
+            if (string.IsNullOrEmpty(text)) return text;
+            return text
+                .Replace("%%p", "±")
+                .Replace("%%P", "±")
+                .Replace("%%d", "°")
+                .Replace("%%D", "°")
+                .Replace("%%c", "⌀")
+                .Replace("%%C", "⌀")
+                .Replace("%%%", "%");
+        }
+
         private void filterPanel_Paint(object sender, PaintEventArgs e)
         {
 

OpenNest/Forms/EditNestForm.cs

@@ -329,7 +329,7 @@ namespace OpenNest.Forms
         {
             var dlg = new OpenFileDialog();
             dlg.Multiselect = true;
-            dlg.Filter = "DXF Files (*.dxf) | *.dxf";
+            dlg.Filter = "CAD Files (*.dxf;*.dwg)|*.dxf;*.dwg|DXF Files (*.dxf)|*.dxf|DWG Files (*.dwg)|*.dwg";
 
             if (dlg.ShowDialog() != DialogResult.OK)
                 return;
@@ -346,7 +346,6 @@ namespace OpenNest.Forms
             drawings.ForEach(d => Nest.Drawings.Add(d));
 
             UpdateDrawingList();
-            tabControl1.SelectedIndex = 1;
         }
 
         public bool Export()

OpenNest/GraphicsHelper.cs

@@ -138,9 +138,20 @@ namespace OpenNest
                         break;
 
                     case CodeType.RapidMove:
-                        cutPath.StartFigure();
-                        leadPath.StartFigure();
-                        AddLine(cutPath, (RapidMove)code, mode, ref curpos);
+                        {
+                            var rapid = (RapidMove)code;
+                            var endpt = rapid.EndPoint;
+                            if (mode == Mode.Incremental)
+                                endpt += curpos;
+                            var dx = endpt.X - curpos.X;
+                            var dy = endpt.Y - curpos.Y;
+                            if (dx * dx + dy * dy > 0.001 * 0.001)
+                            {
+                                cutPath.StartFigure();
+                                leadPath.StartFigure();
+                            }
+                            curpos = endpt;
+                        }
                         break;
 
                     case CodeType.SubProgramCall:
@@ -300,8 +311,17 @@ namespace OpenNest
                         break;
 
                     case CodeType.RapidMove:
-                        Flush();
-                        AddLine(path, (RapidMove)code, mode, ref curpos);
+                        {
+                            var rapid = (RapidMove)code;
+                            var endpt = rapid.EndPoint;
+                            if (mode == Mode.Incremental)
+                                endpt += curpos;
+                            var dx = endpt.X - curpos.X;
+                            var dy = endpt.Y - curpos.Y;
+                            if (dx * dx + dy * dy > 0.001 * 0.001)
+                                Flush();
+                            curpos = endpt;
+                        }
                         break;
 
                     case CodeType.SubProgramCall: