docs: update remnant fill investigation — engine needs more rotation candidates
The engine gets 7 parts where manual nesting gets 9, all at the same rotation. The fix is trying more rotations across all fill strategies. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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# Remnant Fill Optimization Investigation
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# Remnant Fill Optimization — Try More Rotations
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## Problem
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When filling remnant strips on a partially-nested plate, `NestEngine.Fill(NestItem, Box)` produces fewer parts than the UI's Ctrl+F fill. On a test case (N0308-008.zip, 36x36 plate, "Converto 3 YRD DUMPERSTER HINGE PLATE #2" 5.89x3.39):
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`NestEngine.Fill(NestItem, Box)` gets 7 parts in a narrow remnant strip where manual nesting gets 9 — all at the same rotation. The engine simply isn't trying the rotation angle that fits best.
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- **MCP fill_remnants**: 7 parts in the right-side strip
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- **UI Ctrl+F (ActionClone.Fill)**: 9 parts in the same strip
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## Test Case
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## Test Setup
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Load `C:/Users/AJ/Desktop/N0308-008.zip` — 75 parts on a 36x36 plate. Remnant strip is at `(31.0, 0.8) 4.7x35.0`.
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Load `C:/Users/AJ/Desktop/N0308-008.zip` — 75 parts on plate 0, 5 columns of 15. The remnant strip is at `(31.0, 0.8) 4.7x35.0`.
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Use the OpenNest MCP tools to reproduce:
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```
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load_nest("C:/Users/AJ/Desktop/N0308-008.zip")
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get_plate_info(0) → should show 75 parts, remnant at (31.0, 0.8) 4.7x35.0
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fill_remnants(0, "Converto 3 YRD DUMPERSTER HINGE PLATE #2") → gets 7 parts
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fill_remnants(0, "Converto 3 YRD DUMPERSTER HINGE PLATE #2") → gets 7, should get 9
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```
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## Root Cause Analysis
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## Root Cause
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The MCP's `fill_remnants` calls `NestEngine.Fill(NestItem, Box)` which:
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In `NestEngine.Fill(NestItem, Box)` (`OpenNest.Engine/NestEngine.cs:32-105`), the rotation candidates are:
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1. Tries `FillLinear` with best rotation + 90° (and angle sweep if strip is narrow)
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2. Tries `FillRectangleBestFit` (mixes horizontal/vertical in bin packing)
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3. Tries `FillWithPairs` (paired part combinations via `BestFitCache`)
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4. Picks the best result
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1. `bestRotation` from `RotationAnalysis.FindBestRotation(item)`
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2. `bestRotation + 90°`
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3. If the strip is narrow relative to the part, a sweep every 5° from 0° to 175°
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The UI's `ActionClone.Fill()` (`OpenNest/Actions/ActionClone.cs:171-201`) does something different:
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The narrow-strip sweep triggers when `workAreaShortSide < partLongestSide`. For this strip (4.7" wide, part is 5.89x3.39), the short side is 4.7 and the part's longest side is 5.89, so the sweep **should** trigger. But the winning rotation may still not be found because:
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1. Gets `Helper.GetLargestBoxVertically(pt, bounds, boxes)` and `GetLargestBoxHorizontally(pt, bounds, boxes)` from the cursor position
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2. Picks the largest area
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3. Calls `NestEngine.Fill(groupParts, bestArea)` — note: passes `List<Part>` not `NestItem`
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- The sweep only runs on the `bestRotation`-normalized part dimensions
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- `FillLinear` may not be optimal for all angles — check if `FillRectangleBestFit` and `FillWithPairs` are also tried at each sweep angle
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The `Fill(List<Part>, Box)` overload uses `RotationAnalysis.FindHullEdgeAngles(groupParts)` which may produce different/better rotation candidates than `Fill(NestItem, Box)` which uses `RotationAnalysis.FindBestRotation(item)`.
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## Fix
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## Key Differences to Investigate
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Ensure all three fill strategies (FillLinear, FillRectangleBestFit, FillWithPairs) are tried across the full set of rotation candidates, not just FillLinear.
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### 1. Rotation candidate generation
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- `Fill(NestItem, Box)` uses `FindBestRotation` → best angle + 90° + optional sweep
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- `Fill(List<Part>, Box)` uses `FindHullEdgeAngles` → edge angles from convex hull
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- The hull edge angles may include rotation angles that pack better in the narrow strip
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## Files
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### 2. Region selection
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- UI uses cursor position to find the largest obstacle-free rectangle via `GetLargestBoxVertically`/`GetLargestBoxHorizontally`
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- MCP uses `Plate.GetRemnants()` which returns edge strips from global part boundaries
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- The UI region may differ in exact bounds from the remnant strip
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### 3. Part grouping
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- UI's `ActionClone` can pass multi-part groups to `Fill(List<Part>, Box)`, enabling pattern-based tiling
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- MCP passes single `NestItem` to `Fill(NestItem, Box)`
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## Files to Read
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- `OpenNest.Engine/NestEngine.cs` — both `Fill` overloads, `FillWithPairs`, `FillPattern`
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- `OpenNest/Actions/ActionClone.cs:171-201` — the UI fill path
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- `OpenNest.Engine/BestFit/RotationAnalysis.cs` — `FindBestRotation` vs `FindHullEdgeAngles`
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- `OpenNest.Engine/FillLinear.cs` — the linear tiling engine
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- `OpenNest.Core/Helper.cs:1098+` — `GetLargestBoxVertically`/`GetLargestBoxHorizontally`
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## Possible Fixes
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1. **Use hull edge angles in the NestItem overload** — merge rotation candidates from both `FindBestRotation` and `FindHullEdgeAngles`
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2. **Improve GetRemnants** — instead of global edge strips, scan per-column to find the actual free space shape
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3. **Add a smarter fill_remnants** — have the MCP tool use `GetLargestBox*` helpers to find free rectangles from multiple scan points, similar to how the UI does it
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- `OpenNest.Engine/NestEngine.cs:32-105` — `Fill(NestItem, Box)` rotation logic
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- `OpenNest.Engine/BestFit/RotationAnalysis.cs` — `FindBestRotation`
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- `OpenNest.Engine/FillLinear.cs` — linear tiling
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