How to programmatically apply Convex Decomposition with Shrink Wrap to match Isaac Sim UI defaults?

[mattmazzola]

Context

I have a scene containing rigid body prims with meshes which have concave areas.
I apply the Convex Decomposition collision approximation but when visualizing the colliders I can see they are not very accurate to the mesh boundaries.

Notice the cube looks like it is floating off the surface of the tray.

I am using code similar to the following

mesh_collision_api = UsdPhysics.MeshCollisionAPI.Apply(prim)
mesh_collision_api.GetApproximationAttr().Set(UsdPhysics.Tokens.convexDecomposition)

You can see it results in these properties on the mesh prim.

Manual application of Convex Decomposition

I noticed if I toggle the approximation method through the UI, such as changing to Convex Hull and then back to Convex Decomposition, I get an extended set of prim attributes for physxConvexDecompositionCollision

One notable attribute is physxConvexDecompositionCollision:shrinkWrap

If I enable this property, the collider is very accurate and acceptable. 👍

Programmatic Application of Shrink Wrap

The issue I have is that when I try to apply the shrink wrap using code it does NOT behave the same way.

shrink_wrap_attr = prim.CreateAttribute(
    "physxConvexDecompositionCollision:shrinkWrap",
    Sdf.ValueTypeNames.Bool,
)
if shrink_wrap_attr is not None:
    shrink_wrap_attr.Set(apply_shrink_wrap_for_decomposition)

This does apply the shrink wrap effect; however, the approximation is different, notice the smaller gap.

Also, I do NOT see the attribute in shown next to other Collider > Advanced properties

It is only in the RAW USD Properties

Question

How to programmatically apply Collision API with Convex Decomposition approximation using Shrink Wrap to match the UI?

I realize I could use omni.kit.commands.execute('ChangeProperty', ....) commands but I would like to avoid this.

Perhaps there is a special Convex Decomposition Collision API I can apply to the prim?

[mattmazzola]

Ok, I think I found a solution

physx_convexdecomp_api = PhysxSchema.PhysxConvexDecompositionCollisionAPI.Apply(prim)
physx_convexdecomp_api.GetShrinkWrapAttr().Set(True)

It is hard to know about these APIs to the lack of typing information in the code.

See other forum issue: How to get python typing information for the pxr PhysxSchema? - Omniverse / Isaac Sim - NVIDIA Developer Forums

Docs: PhysxSchemaPhysxConvexDecompositionCollisionAPI Class Reference (nvidia.com)

The tray collider mesh is now approximating well and the cube appears to rest on it as expected.