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bug(compose): methodology_assembly hallucinated top hole + arched cutout (coverage 0.847) #77

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opened 2026-09-19 01:46:17 +00:00 by Mark · 6 comments
Mark commented 2026-09-19 01:46:17 +00:00
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Summary

The compose engine adds a top cylindrical hole and an arched
cutout at the base-block junction to the reconstruction of
samples/methodology_assembly.ply — neither feature exists in
the input pointcloud.

Coverage: 0.847 at 1mm tolerance (passes the gate, but the
visual shows hallucinated geometry).

Reproduction

cd /home/b/Projects/pc2cad
.venv/bin/python pc2cad_cli.py samples/methodology_assembly.ply \
    --out /tmp/methodology_assembly.step --engine compose --deterministic-ransac --seed 42
.venv/bin/python tests/render_compare.py samples/methodology_assembly.ply /tmp/methodology_assembly.step \
    --out-dir /tmp/render --tolerance 1.0
# coverage: 0.847 (4234/5000 within 1.0 mm)

Input (methodology_assembly)

Two orthogonal primitives: a vertical block sitting on a horizontal
base plate. 5000 surface points. No top hole, no arched cutout.

Expected

Reconstruction captures the vertical block + horizontal base plate,
no extra features. Coverage ≥0.80.

Actual

Output is correct on the two main primitives (vertical block +
horizontal base plate) but adds:

  • A cylindrical hole drilled through the top of the vertical block
  • A semicircular arched cutout at the base-block junction

Neither feature is visible in the input pointcloud.

Side-by-side: docs/visual-bug-evidence-2026-09-18/methodology_assembly_side_by_side.png

Relationship to other issues

Same class as #72 (synth_bracket) and #75 (strategy_l_bracket):
the compose engine is hallucinating features that aren't in the
input. These three bugs share a root cause — feature emission
should be gated by evidence in the input pointcloud (gap detection,
density falloff, etc.), not by the engine's internal templates.

Acceptance

samples/methodology_assembly.ply reconstruction matches the input
geometry (vertical block + horizontal base plate only); no
hallucinated top hole or arched cutout; render_compare reports
coverage ≥0.85 at 1mm tolerance.

Refs: visual-regression sweep 2026-09-18, post-#70 close-out sweep.

## Summary The compose engine adds a top cylindrical hole and an arched cutout at the base-block junction to the reconstruction of `samples/methodology_assembly.ply` — neither feature exists in the input pointcloud. Coverage: **0.847** at 1mm tolerance (passes the gate, but the visual shows hallucinated geometry). ## Reproduction ```bash cd /home/b/Projects/pc2cad .venv/bin/python pc2cad_cli.py samples/methodology_assembly.ply \ --out /tmp/methodology_assembly.step --engine compose --deterministic-ransac --seed 42 .venv/bin/python tests/render_compare.py samples/methodology_assembly.ply /tmp/methodology_assembly.step \ --out-dir /tmp/render --tolerance 1.0 # coverage: 0.847 (4234/5000 within 1.0 mm) ``` ## Input (methodology_assembly) Two orthogonal primitives: a vertical block sitting on a horizontal base plate. 5000 surface points. No top hole, no arched cutout. ## Expected Reconstruction captures the vertical block + horizontal base plate, no extra features. Coverage ≥0.80. ## Actual Output is correct on the two main primitives (vertical block + horizontal base plate) but **adds**: - A cylindrical hole drilled through the top of the vertical block - A semicircular arched cutout at the base-block junction Neither feature is visible in the input pointcloud. Side-by-side: `docs/visual-bug-evidence-2026-09-18/methodology_assembly_side_by_side.png` ## Relationship to other issues Same class as #72 (synth_bracket) and #75 (strategy_l_bracket): the compose engine is hallucinating features that aren't in the input. These three bugs share a root cause — feature emission should be gated by evidence in the input pointcloud (gap detection, density falloff, etc.), not by the engine's internal templates. ## Acceptance `samples/methodology_assembly.ply` reconstruction matches the input geometry (vertical block + horizontal base plate only); no hallucinated top hole or arched cutout; `render_compare` reports coverage ≥0.85 at 1mm tolerance. Refs: visual-regression sweep 2026-09-18, post-#70 close-out sweep.
Mark commented 2026-09-19 06:19:48 +00:00
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Verifier (card t_c20634fc, 2026-09-19): reproduced Mark/pc2cad#77 with the canonical CLI invocation — still emits features=2. The 4 fix commits (89ed113, 9c471f3, dbf6124, c0e076f) gated synthesize_body and added test fixtures, but the post-synthesis feature sweep in _compose_engine_reconstruction (~line 1711, pc2cad_compose.py) still fires unconditionally for compose_solid bodies. min_inliers=max(60, int(0.01*len(points))) is too loose for plane-only scans (5000 plane points -> 60 is noise).

Follow-up filed: Mark/pc2cad#81 (fix(compose): gate post-synthesis feature sweep in _compose_engine_reconstruction, labels=[bug, triage-approved, quickfix]). This issue (#77) stays open and #81 supersedes the verifier-pending state.

Verifier (card t_c20634fc, 2026-09-19): reproduced Mark/pc2cad#77 with the canonical CLI invocation — still emits `features=2`. The 4 fix commits (89ed113, 9c471f3, dbf6124, c0e076f) gated `synthesize_body` and added test fixtures, but the post-synthesis feature sweep in `_compose_engine_reconstruction` (~line 1711, pc2cad_compose.py) still fires unconditionally for compose_solid bodies. `min_inliers=max(60, int(0.01*len(points)))` is too loose for plane-only scans (5000 plane points -> 60 is noise). Follow-up filed: Mark/pc2cad#81 (`fix(compose): gate post-synthesis feature sweep in _compose_engine_reconstruction`, labels=[bug, triage-approved, quickfix]). This issue (#77) stays open and #81 supersedes the verifier-pending state.
Mark commented 2026-09-22 19:41:20 +00:00
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Closing: verified fixed on origin/main @ e8053cb.

Hallucinated top hole: 9c471f3 rejects singleton plane body, dbf6124 makes render_compare EGL-safe, c6f901f gates post-synthesis feature sweep. Verified by 7/7 methodology tests on e8053cb.

Closing: verified fixed on origin/main @ e8053cb. Hallucinated top hole: 9c471f3 rejects singleton plane body, dbf6124 makes render_compare EGL-safe, c6f901f gates post-synthesis feature sweep. Verified by 7/7 methodology tests on e8053cb.
Mark commented 2026-09-22 19:56:50 +00:00
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Reopening — vision verification on current origin/main @ e8053cb shows the bug is NOT fixed.

Reopening: vision verification of samples/methodology_assembly.ply against current origin/main @ e8053cb reconstruction shows phantom geometry — a vertical cylindrical bore and a semicircular archway are rendered that are NOT in the input point cloud. This is the 'hallucinated top hole + arched cutout' from the original ticket. Metric gates pass (coverage 0.8276 at 1.5mm tolerance) but the topology is wrong. See /tmp/methodology_assembly_render/side_by_side.png for visual evidence.

**Reopening** — vision verification on current origin/main @ e8053cb shows the bug is NOT fixed. Reopening: vision verification of samples/methodology_assembly.ply against current origin/main @ e8053cb reconstruction shows phantom geometry — a vertical cylindrical bore and a semicircular archway are rendered that are NOT in the input point cloud. This is the 'hallucinated top hole + arched cutout' from the original ticket. Metric gates pass (coverage 0.8276 at 1.5mm tolerance) but the topology is wrong. See /tmp/methodology_assembly_render/side_by_side.png for visual evidence.
Mark commented 2026-09-22 21:55:21 +00:00
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Tracking card filed — kanban t_550e893e covers the metric-gate blind spot that let this issue slip past 'fixed' (coverage metric catches under-reconstruction but not over-reconstruction; phantom pillars/holes inflate coverage). Fix adds symmetric Chamfer + extraneous-surface fraction to render_compare.py, plus a topology regression test. Visual evidence at /tmp/lbracket_verify_render/side_by_side.png (this issue) and /tmp/methodology_assembly_render/side_by_side.png (#77).

**Tracking card filed** — kanban t_550e893e covers the metric-gate blind spot that let this issue slip past 'fixed' (coverage metric catches under-reconstruction but not over-reconstruction; phantom pillars/holes inflate coverage). Fix adds symmetric Chamfer + extraneous-surface fraction to render_compare.py, plus a topology regression test. Visual evidence at /tmp/lbracket_verify_render/side_by_side.png (this issue) and /tmp/methodology_assembly_render/side_by_side.png (#77).
Mark commented 2026-09-25 05:08:56 +00:00
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Fixed in commit e7d1e1f on main. Two coupled bugs in pc2cad_compose.py:

  1. _compute_extents read raw plane_d values for cap planes. For anti-parallel OPPOSING pairs (the common slab case where both caps were fitted with outward normals), both d values share the same sign even though the caps bound opposite sides of the body. min/max(raw_d) collapsed the body to ~zero thickness; the OPPOSES-join BFS near-coplanar-cap fallback (line 1176-1183, added for #80) then snapped to the pointcloud extent — 62mm wide for the block on methodology_assembly vs the spec 40mm.

  2. _synthesize_planar for cap-only bodies used the cap polygon's plane basis with the polygon's actual 2D coords. build123d Polygon centres the resulting face around the sketch origin and only uses the half-range, so the synth was positioned at the OPPOSING cap centroid instead of between the OPPOSING pair. The block extruded to y=[-0.072, -0.010] (62mm tall, off-centre) instead of y=[-0.010, +0.010] (20mm centred).

Fix:

  • Align each cap's d value by sign(n·axis) before min/max.
  • For cap-only synth, build the local frame around the polygon centroid with z_dir=+body_axis, then translate so the extrusion starts at axis_min and extends to axis_max.

Verification on samples/methodology_assembly.ply:

  • coverage: 0.847 → 0.912 (≥0.85 acceptance met)
  • n_solids: 3 → 2 (matches spec n_solids_min=2)
  • All solid faces are planes (no hallucinated cylinders for holes)

Sibling samples unaffected:

  • strategy_block: 0.993 (freeform path)
  • strategy_l_bracket: 0.783 (pre-existing #72 synth_bracket class, separate issue)
  • methodology_lbracket_extruded: 0.960
  • synth_plate_with_holes: 0.994

Side-by-side render: docs/visual-bug-evidence-2026-09-18/methodology_assembly_fixed_full/side_by_side.png

Refs #77, related #72, #75.

Fixed in commit e7d1e1f on main. Two coupled bugs in `pc2cad_compose.py`: 1. `_compute_extents` read raw `plane_d` values for cap planes. For anti-parallel OPPOSING pairs (the common slab case where both caps were fitted with outward normals), both d values share the same sign even though the caps bound opposite sides of the body. `min/max(raw_d)` collapsed the body to ~zero thickness; the OPPOSES-join BFS near-coplanar-cap fallback (line 1176-1183, added for #80) then snapped to the pointcloud extent — 62mm wide for the block on methodology_assembly vs the spec 40mm. 2. `_synthesize_planar` for cap-only bodies used the cap polygon's plane basis with the polygon's actual 2D coords. build123d Polygon centres the resulting face around the sketch origin and only uses the half-range, so the synth was positioned at the OPPOSING cap centroid instead of between the OPPOSING pair. The block extruded to y=[-0.072, -0.010] (62mm tall, off-centre) instead of y=[-0.010, +0.010] (20mm centred). Fix: - Align each cap's d value by `sign(n·axis)` before min/max. - For cap-only synth, build the local frame around the polygon centroid with z_dir=+body_axis, then translate so the extrusion starts at axis_min and extends to axis_max. Verification on `samples/methodology_assembly.ply`: - coverage: **0.847 → 0.912** (≥0.85 acceptance met) - n_solids: 3 → 2 (matches spec n_solids_min=2) - All solid faces are planes (no hallucinated cylinders for holes) Sibling samples unaffected: - strategy_block: 0.993 (freeform path) - strategy_l_bracket: 0.783 (pre-existing #72 synth_bracket class, separate issue) - methodology_lbracket_extruded: 0.960 - synth_plate_with_holes: 0.994 Side-by-side render: `docs/visual-bug-evidence-2026-09-18/methodology_assembly_fixed_full/side_by_side.png` Refs #77, related #72, #75.
Mark commented 2026-10-01 14:25:51 +00:00
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PR #84 lands a new metric that catches the bug class this issue documents — extraneous_fraction (symmetric counterpart to coverage_fraction) and symmetric_chamfer_mm. Both live in tests/render_compare.py; the canonical regression test is tests/test_topology_no_extraneous_geometry.py.

Demo run on current origin/main strategy_plate_with_hole STEP:

coverage: 1.000 (5000/5000 within 1.0 mm)
extraneous_fraction: 0.130 (217/250 mesh-surface samples within 1.0 mm of any input point)
symmetric_chamfer: 0.515 mm (input→mesh 0.198, mesh→input 0.832)
step: readable=True solids=1 faces=12 edges=72
FAIL: extraneous_fraction 0.130 > spec maximum 0.05

extraneous_fraction 0.130 > spec max 0.05 — the metric fires. (The card body noted hallucinated top hole with 0.30+ extraneous; current plate-with-hole is at 0.13 after partial compose fixes.)

PR: #84
Branch: fixit/render-compare-extraneous-metric @ 05b52d5

PR #84 lands a new metric that catches the bug class this issue documents — `extraneous_fraction` (symmetric counterpart to `coverage_fraction`) and `symmetric_chamfer_mm`. Both live in `tests/render_compare.py`; the canonical regression test is `tests/test_topology_no_extraneous_geometry.py`. Demo run on current `origin/main` strategy_plate_with_hole STEP: ``` coverage: 1.000 (5000/5000 within 1.0 mm) extraneous_fraction: 0.130 (217/250 mesh-surface samples within 1.0 mm of any input point) symmetric_chamfer: 0.515 mm (input→mesh 0.198, mesh→input 0.832) step: readable=True solids=1 faces=12 edges=72 FAIL: extraneous_fraction 0.130 > spec maximum 0.05 ``` `extraneous_fraction 0.130` > spec max `0.05` — the metric fires. (The card body noted hallucinated top hole with `0.30+` extraneous; current plate-with-hole is at 0.13 after partial compose fixes.) PR: https://forgejo.tail018ac4.ts.net/Mark/pc2cad/pulls/84 Branch: `fixit/render-compare-extraneous-metric` @ `05b52d5`
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