How to get the surface normals of the USD model in IsaacSim?

Omniverse Isaac Sim
,
1

I want to annotate some labels relative to the geometry on the USD model in IsaacSim, so I need to get the surface normals on the mesh, but the function UsdGeom.Mesh.GetNormalsAttr().Get() seems only return the normal vectors without their position, and the number of the normals are neither the same as the number of faces or the number of vertexs. The interpolation method got from GetNormalsInterpolation() is “faceVarying”, in such condition how can I get the correspounding position of the normals?

The code I used is as follows:

dest_path = 'bottle.usd'
omni.usd.get_context().open_stage(dest_path)
while is_stage_loading():
    simulation_app.update()
stage = get_current_stage()
root_prim = stage.GetDefaultPrim()
if not root_prim.HasProperty('physics:rigidBodyEnabled'):
    omni.kit.commands.execute('AddPhysicsComponent', usd_prim=root_prim, component='PhysicsRigidBodyAPI')
for prim in stage.Traverse():
    prim: Usd.Prim
    if prim.GetTypeName() == 'Mesh':
        if prim.GetAttribute('visibility').Get() == 'invisible':
            continue

        omni.kit.commands.execute('SetStaticCollider', path=prim.GetPath(), approximationShape='convexDecomposition')
        mesh = UsdGeom.Mesh(prim)
        points = np.array(mesh.GetPointsAttr().Get())
        normals = np.array(mesh.GetNormalsAttr().Get())
        print(points.shape)      # [2564, 3]
        print(normals.shape)   # [14058, 3]
        print(mesh.GetPrim().GetAttribute("primvars:normals").Get())  # None
3

Surface normals can be extracted with a Replicator custom writer. Writers use annotators to request GT, such as normals, from rendering. Please refer to this example on the Replicator normals annotator.