Object fixes: collision geometry, coordinate frames, mesh alignment

[siddhss5]

Convention

• Origin at bottom center (canonical resting pose, Z-up)
• dimensions[2] is always the resting height
• Collision geom aligned with visual mesh
• Visual mesh centered at origin in mesh file (no pos/euler offsets in XML)

Verification Status

Object	Collision Geom	Coll/Render Align	Coord Frame	Mesh Z	Notes
can	✅	✅	✅	✅
cracker_box	✅	✅	✅	✅	mesh re-centered
fuze_bottle	✅	✅	✅	✅	mesh re-centered
gelatin_box	✅	✅	✅	✅	mesh re-centered + rotated
herring_tin	🔧	🔧	🔧	🔧	box+2cyl collision, dims swapped to resting frame
lunchbox	✅	✅	🔧	🔧	rotated to flat pose, collision fits main body
notebook	✅	🔧	✅	✅	mesh re-centered
plastic_bowl	🔧	🔧	🔧	✅	mesh collision + solref/solimp for nesting
plastic_glass	🔧	🔧	🔧	✅	cylinder collision with pos offset
plastic_plate	🔧	🔧	🔧	✅	mesh collision + solref/solimp for stacking
pocky_box	✅	✅	✅	✅
pop_tarts	✅	✅	✅	✅	mesh re-centered + rotated
potted_meat_can	✅	✅	✅	✅	mesh re-centered
recycle_bin	✅	✅	✅	n/a	primitives only
sugar_box	✅	🔧	🔧	🔧	rotated to flat pose
wicker_tray	✅	✅	✅	✅	hollow tray primitives
yellow_tote	✅	🔧	✅	✅	hollow tote primitives, mesh shifted

Legend: ✅ verified, 🔧 needs fix

Objects needing work

• herring_tin — all 4 criteria
• plastic_bowl — collision, alignment, coord frame
• plastic_glass — collision, alignment, coord frame
• plastic_plate — collision, alignment, coord frame
• sugar_box — alignment, coord frame, mesh Z
• lunchbox — coord frame, mesh Z
• notebook — alignment
• yellow_tote — alignment

Useful scripts (already in repo)

• scripts/validate_objects.py — check all 6 criteria
• scripts/inspect_object.py — visual inspection with collision overlay + axes
• scripts/recenter_mesh.py — re-center mesh origin to centroid
• scripts/viz_all_objects.py — grid view with collision overlays
• scripts/viz_stacking_demo.py — physics demo with stacked dishes

Workflow

1. uv run python scripts/validate_objects.py <object>
2. uv run python scripts/inspect_object.py <object>
3. uv run python scripts/recenter_mesh.py path/to/mesh.obj --apply
4. Re-validate and visually verify

Key lessons

• dimensions[2] must be the resting height (thin dimension for flat objects like herring_tin)
• Mesh must be centered at centroid; use body pos for z-offset, not mesh origin
• Don't use pos/euler on visual geoms — fix the mesh file directly
• Tall thin objects (glass) work better with cylinder primitive than mesh collision
• Mesh collision for nesting (bowls, plates) needs solref="0.004 1" solimp="0.95 0.99 0.001"
• When primitive collision has its own pos, keep body pos="0 0 0"
• Physics stacking demos need integrator="implicitfast" and viscosity="2.0"