LiEdi Physics Fixer

USD physics diagnostics and structure repair extension for NVIDIA Isaac Sim. The tool scans a loaded stage, reports structural physics issues, and applies targeted fixes for common asset-side failures.

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1. Development Background

Isaac Sim physics workflows often require manual inspection across multiple nested USD prims and API bindings. Existing debugger-style tools are useful for runtime diagnosis, but they can be slow to navigate when the problem is a static asset issue.

LiEdi focuses on the asset-repair path:

• inspect the USD stage directly
• detect common physics schema conflicts
• generate a readable diff-style summary
• apply deterministic fixes to the stage

The goal is to keep the workflow short and mechanical: scan, inspect, fix, verify.

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2. Core Features (First Release)

This first release targets six recurring failure modes that commonly break simulation stability or prevent articulation from behaving as expected:

1. Root & Prim API Conflict

   • Issue: A prim carries both UsdPhysics.ArticulationRootAPI and UsdPhysics.RigidBodyAPI.
   • Fix: Removes the conflicting rigid body schema from the articulation root.

2. Nested RigidBody Conflict

   • Issue: A rigid body is nested under another rigid body without an explicit joint boundary.
   • Fix: Rehomes the child under a non-rigid parent or scene root.

3. Joint Missing RigidBodyAPI

   • Issue: A UsdPhysics.Joint points to a target missing RigidBodyAPI.
   • Fix: Applies the missing rigid body schema to the joint target.

4. Invalid Joint Limits

   • Issue: Joint limits are inverted, with lowerLimit > upperLimit.
   • Fix: Normalizes the limit ordering.

5. Inactive Drive Parameters

   • Issue: A joint has DriveAPI enabled, but both stiffness and damping are zero.
   • Fix: Restores non-zero drive gains.

6. Missing/Invalid Mass & Inertia

   • Issue: Mass properties are missing or inertia values collapse toward zero.
   • Fix: Ensures explicit mass metadata with valid inertia values.

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3. How to Use

1. Launch Isaac Sim and enable the extension from Window > Extensions.
2. Open Utilities > LiEdi Phys Fix.
3. Run Scan Stage on the active USD stage.
4. Review the diff panel and apply the suggested fix set.
5. Re-run the scan to confirm the stage is clean.

Expected output:

• a list of detected physics schema issues
• a diff-style preview of intended edits
• an applied stage patch when the fix action is accepted