Exclude relation anchors from background collision meshes

[qianl-nv]

Summary

Exclude anchored references from background meshes

Detailed description

• Prevent conflicting relation and mesh-collision constraints for anchored object references.
• Exclude referenced USD prim subtrees when aggregating their parent background mesh.
• Include exclusions in mesh-cache keys and handle fully excluded geometry.
• Add coverage for exclusion propagation, extraction, and cache behavior.

Command to run:
/isaac-sim/python.sh isaaclab_arena/evaluation/policy_runner.py --viz kit --policy_type zero_action --num_episodes 20 --disable_fabric --device cpu --env_graph_spec_yaml isaaclab_arena_environments/kitchen_bench/replicator_kitchen_peninsula_mustard_bowl.yam

Before:
[RelationSolver] solve: 3635.3 ms | batch=50 | objects=3 optimizable + 2 anchors | no-overlap pairs=9 | iters=600 (6.06 ms/iter)
[placement] Validated 50 candidate layout(s); passed per check: on_relation=0/50, next_to=34/50, not_next_to=50/50, face_to=50/50, no_overlap=34/50

After:
[RelationSolver] solve: 3392.7 ms | batch=50 | objects=3 optimizable + 2 anchors | no-overlap pairs=9 | iters=600 (5.65 ms/iter)
[placement] Validated 50 candidate layout(s); passed per check: on_relation=35/50, next_to=35/50, not_next_to=50/50, face_to=50/50, no_overlap=47/50

[qianl-nv]

self review 1

[greptile-apps]

Greptile Summary

Excludes anchored object-reference subtrees when aggregating parent USD geometry into background collision meshes.

• Resolves and caches each reference's parent-USD prim path alongside its relative pose.
• Propagates anchored-reference exclusions through passive collision discovery and fixed-mesh aggregation.
• Includes normalized exclusion sets in collision-mesh cache keys and distinguishes fully excluded geometry.
• Adds coverage for exclusion propagation, extraction behavior, and cache isolation.

Confidence Score: 5/5

The PR appears safe to merge; no concrete changed-code failure remains.

The exclusion path preserves scene-object identity, uses correctly delimited absolute USD subtree paths, and separates cached meshes by their exclusion sets.

Important Files Changed

Filename	Overview
isaaclab_arena/assets/object_reference.py	Resolves and retains the referenced absolute USD path while preserving the existing relative-pose calculation.
isaaclab_arena/environments/relation_solver_interface.py	Collects anchored ObjectReferences and forwards them to passive background collision discovery.
isaaclab_arena/relations/passive_collision_objects.py	Groups reference exclusions by the same parent objects selected for aggregate collision processing.
isaaclab_arena/relations/background_collision_object.py	Propagates per-object USD subtree exclusions into fixed collision-mesh extraction.
isaaclab_arena/relations/warp_mesh_manager.py	Keys extracted meshes by normalized exclusions and forwards exclusions to the USD extractor.
isaaclab_arena/utils/usd_helpers.py	Omits exact prim subtrees during traversal and reports when exclusions remove all mesh geometry.
isaaclab_arena/tests/test_relation_solver_background_collision.py	Covers exclusion forwarding, grouping, cache separation, and background extraction failure behavior.
isaaclab_arena/tests/test_usd_helpers.py	Adds simulator-backed coverage for complete exclusions and malformed remaining geometry.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart LR
  A[Anchored ObjectReference] --> B[Resolve parent USD prim path]
  B --> C[Collect exclusions by parent asset]
  C --> D[Passive collision discovery]
  D --> E[Fixed background mesh aggregation]
  E --> F[USD mesh extraction]
  C --> G[Cache key: USD path + scale + exclusions]
  F --> H[Background collision mesh without anchor subtree]

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_{Reviews (1): Last reviewed commit: "Exclude relation anchors from background..." | Re-trigger Greptile}

[arena-review-bot]

🤖 Isaac Lab-Arena Review Bot

Summary

This PR stops anchored object references from being counted twice in placement collision — once as their own anchor collision mesh and again inside the aggregated background mesh — by threading per-object USD subtree exclusions from the solver interface down through mesh extraction. The change is well-layered (pxr imports stay deferred, exclusions live in the domain/relations layer), the cache key correctly incorporates exclusions, subtree matching avoids prefix false-positives (startswith(f"{path}/")), and the reported on_relation / no_overlap gains confirm it fixes a real conflict. Solid, focused work.

Findings

🔵 usd_helpers.py:369 — When exclusions remove every mesh from a background, the new NoCollisionMeshError ultimately trips the whole-scene-Background assertion and aborts placement. Raised as a question: is a hard crash intended, or should a background whose geometry is fully covered by anchors simply contribute no mesh? (See inline.)

Test Coverage

Strong. New coverage spans exclusion propagation (test_passive_background_excludes_relation_anchor_subtrees), cache keying by exclusions (test_warp_mesh_cache_keys_exclusions), the fully-excluded and unsupported-geometry error paths, prim-path caching, and an inner/outer sim test (test_mesh_exclusion_errors) exercising real USD extraction. The interface-level forwarding test correctly patches get_passive_collision_objects at its source module to match the new lazy import.

Verdict

Ship it — the one finding is an open design question, not a blocker.

[zhx06]

LGTM! The only nit is the comments from the arena review bot, whether excluding all meshes should be treated as an error. Everything else looks good.