capwitf/mechanical-cad-skills/cad-reference-acceptance

CAD Reference Acceptance

Core Rule

Never accept a reference-matched CAD/drawing result from whole-page appearance, file validity, entity count, or one broad crop. A match claim needs numbered local-region evidence from the final delivered file.

Observed failure this skill prevents: a hand-redrawn mechanical sheet passed file checks and coarse crop checks, but failed when split into 16 numbered cells.

Acceptance Gate

Use this gate before saying a reference match is ready:

1. Fix the reference source path and final output path.
2. Render or open the final output, not a working preview.
3. Split both into a numbered grid; default is 4x4, numbered left-to-right, top-to-bottom.
4. Compare each cell for pixel similarity, edge difference, line density, text/leader placement, holes, hatches, dimensions, and view boundaries.
5. List the worst cells and root class: geometry, proportion, line type, hatch, annotation, layout, export, or stale file.
6. If any required cell fails, fix the source of truth and regenerate.
7. Save the grid overlay, side-by-side grid, CSV/JSON metrics, and final file evidence.

Do not bury weak cells inside a good average. Report minimum score and worst cell IDs.

Default Thresholds

Use thresholds as tripwires, not proof:

If the reference is a noisy scan, photo, compressed image, or intentionally redrawn semantic CAD, adjust thresholds but state the reason.

Visual vs Editable CAD

Choose and state the target:

Do not deliver a traced outline file while implying it is an editable engineering drawing. Do not deliver editable but rough CAD while implying visual replication.

Script

Use scripts/grid_acceptance.py when reference and output can be rendered as images or PDFs:

python .\.codex\skills\cad-reference-acceptance\scripts\grid_acceptance.py `
  --reference .\reference.png `
  --candidate .\output.pdf `
  --output-dir .\deliverables\acceptance `
  --rows 4 --cols 4 `
  --min-similarity 0.94 `
  --max-edge-diff 0.08

The script writes:

• grid_acceptance.json
• grid_acceptance.csv
• reference_grid.png
• candidate_grid.png
• side_by_side_grid.png

Required Report

Report:

• reference source used,
• final output file checked,
• grid size and thresholds,
• min/average similarity,
• worst cell IDs,
• whether all cells passed,
• root causes for failed cells,
• final file checks and any unverified claims.

Common Mistakes

• Treating PDF/DXF/DWG existence as match evidence.
• Comparing only the whole sheet or one large view crop.
• Reporting average similarity without the minimum and worst cells.
• Comparing a preview while delivering a stale CAD file.
• Mixing visual-trace output with editable-CAD claims.