Rotating a prim around the center (0,0,0) or another prim using an Action Graph

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1

Hi, here’s my Action Graph that rotates my cube around its Y axis. How do I alter it to make the cube rotate around another prim/or a center point at (0,0,0)?

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2

The easiest method is to just parent that cube to an xform and offset it from the xform some amount. Then rotate the xform instead.

3

Hi Richard3D, thanks for your reply. I’d like the cube to rotate around another prim regardless of either hierarchy, eg. if either hierarchy changes in any way, the prims become re-parented or moved to separate hierarchies etc.

I’m trying to script constraints using the UsdGeomConstraintTarget class: Universal Scene Description: UsdGeomConstraintTarget Class Reference

Here’s my .usd scene in which I’d like to create a constraint between my cube and cylinder, so that when cylinder rotates around it’s Y axis for example, the cube rotates around it. I’m looking into contraints bc the prims’ hierarchy will change:

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the constraintTarget gets added to Cube, but when I rotate the Cylinder which I’d like to be cube’s pivot, the cube doesn’t rotate.

Here’s the code:

context = omni.usd.get_context()
    context.open_stage('C:/adding_constraints.usd')
    stage = context.get_stage() 
    
    cube_prim = stage.GetPrimAtPath("/World/Cube")
    cylinder_prim = stage.GetPrimAtPath("/World/Cylinder")
    current_frame = Usd.TimeCode.Default()
    xform_cache = UsdGeom.XformCache(current_frame)

    cube_prim.SetMetadata('kind', 'component')
    
    cube_matrix4d = UsdGeom.XformCache.GetLocalToWorldTransform(xform_cache, cube_prim)
    cylinder_matrix4d = UsdGeom.XformCache.GetLocalToWorldTransform(xform_cache, cylinder_prim)
    cube_prim_ModelAPI = UsdGeom.ModelAPI(cube_prim) 
    
    root_xformable = UsdGeom.Xform.Define(stage, '/World/Cylinder') 
    root_xformable.MakeMatrixXform().Set(cylinder_matrix4d)  

    constraint_target = cube_prim_ModelAPI.CreateConstraintTarget("Cylinder") 
    constraint_target.SetIdentifier('Cylinder')

    localConstraintSpace = cube_matrix4d.SetRotate(
            Gf.Rotation(Gf.Vec3d(0, 1, 0), 45)) 
    
    result_matrix = localConstraintSpace * cube_matrix4d

    stage.GetRootLayer().Save()

I’ve used unittest script for UsdGeomConstraintTarget as a template: https://github.com/sideeffects/USD/blob/29ffeac008c089b5b0c6a66cd668b3c709a07a2a/pxr/usd/usdGeom/testenv/testUsdGeomConstraintTarget.py

The ConstraintTarget I create here isn’t valid (constraint_target.IsValid() results in False):
constraint_target = cube_prim_ModelAPI.CreateConstraintTarget("Cylinder")
The “Cylinder” argument has got to be the problem.