Compare 3D CAD models using boolean operations (IoU, Dice, precision/recall). Use when evaluating generated models against gold references, diffing CAD revisions, or computing similarity metrics for ML training. Triggers on: model diff, compare models, IoU, intersection over union, model similarity, CAD comparison, STEP diff, 3D evaluation, gold reference, generated model, precision recall 3D.
View on GitHubplugins/build123d/skills/model-compare/SKILL.md
January 21, 2026
Select agents to install to:
npx add-skill https://github.com/rawwerks/VibeCAD/blob/main/plugins/build123d/skills/model-compare/SKILL.md -a claude-code --skill model-compareInstallation paths:
.claude/skills/model-compare/# 3D Model Comparison Tool Compare CAD models using boolean operations to compute similarity metrics like IoU, Dice, precision, and recall. Useful for: - Evaluating ML-generated models against gold references - Comparing revisions of CAD designs - Computing metrics for training 3D generative models - Visualizing geometric differences ## Quick Start ```bash # Compare two STEP files uvx --from build123d python scripts/model_diff.py reference.step generated.step # JSON output for training pipelines uvx --from build123d python scripts/model_diff.py ref.step gen.step --json --no-export # Demo mode (no files needed) uvx --from build123d python scripts/model_diff.py --demo ``` ## Supported Formats | Format | Extension | Notes | |--------|-----------|-------| | STEP | `.step`, `.stp` | Recommended - full CAD fidelity | | BREP | `.brep` | OpenCASCADE native format | | STL | `.stl` | Mesh format - may have boolean issues | ## Output Metrics ### Primary Metrics (for ML training) | Metric | Range | Description | |--------|-------|-------------| | **IoU** (Jaccard) | 0-1 | `|A∩B| / |A∪B|` - standard similarity | | **Dice** (F1) | 0-1 | `2|A∩B| / (|A|+|B|)` - more sensitive to small overlaps | | **Precision** | 0-1 | `|A∩B| / |B|` - how much of generated is correct | | **Recall** | 0-1 | `|A∩B| / |A|` - how much of reference was captured | ### Diagnostic Metrics | Metric | Description | |--------|-------------| | `volume_ratio` | B/A volume ratio (1.0 = same size) | | `center_offset` | Distance between centers of mass | | `bbox_iou` | Bounding box IoU (coarse alignment) | | `size_ratio_x/y/z` | Per-axis scale comparison | | `surface_ratio` | Surface area comparison | ### Interpretation The tool provides automatic interpretation: - **Over-generating**: Low precision, high extra geometry - **Under-generating**: Low recall, missing geometry - **Size issues**: Volume ratio far from 1.0 - **Position issues**: Large center offset ## CLI Options ``` usage: model_diff.py