Exercise: Groups#

In this exercise, we recreated the city_blockA assembly asset, but we will show the use of the group kind to section our buildings in the model hierarchy into the north and south sides of the street.

  1. In Visual Studio Code, open the following file: asset_structure/exercise_11/create_assembly_with_groups.py

  2. Add the code below into the designated section:

 1### Update - Added for loop for street sides
 2for side in Side:
 3    ### Update - Added an intermediate group prim between /World and the building references.
 4    side_xform = UsdGeom.Xform.Define(stage, world_prim.GetPath().AppendChild(side.name))
 5    Usd.ModelAPI(side_xform).SetKind(Kind.Tokens.group)
 6    for x in range(1,4):
 7        ref_path: Sdf.Path = side_xform.GetPath().AppendChild(f"lrg_bldgF_{x:02}")
 8        ref_target_prim = UsdGeom.Xform.Define(stage, ref_path).GetPrim()
 9        ref_target_prim.GetReferences().AddReference("./lrg_bldgF/lrg_bldgF.usd")
10        position_bldg(ref_target_prim, x, side)
11

Here we create two group kind prims, North and South. We’ve updated the code to reference three buildings under each group. The position_bldg() function has also been updated to accommodate for this.

  1. Save the file and then execute the script using the following command:

Windows:

python .\asset_structure\exercise_11\create_assembly_with_groups.py

Linux:

python ./asset_structure/exercise_11/create_assembly_with_groups.py

  1. Run the following command to open the output city_blockA in usdview:

Windows:

.\scripts\usdview.bat .\asset_structure\exercise_11\city_blockA.usd

Linux:

./scripts/usdview.sh ./asset_structure/exercise_11/city_blockA.usd

Note that there are no visual changes compared to the “Assemblies” exercise. However, we have made a structural change to the scenegraph, as you can see in the tree view.

  1. In usdview, click on the “North” or “South” prim. We can see in the Meta Data tab that the kind field is set to group.

We have successfully created a valid model hierarchy:

    World (assembly)  
        North (group)  
            lrg_bldgF_01 (component)  
            lrg_bldgF_02 (component)  
            lrg_bldgF_03 (component)  
        South (group)  
            lrg_bldgF_01 (component)  
            lrg_bldgF_02 (component)  
            lrg_bldgF_03 (component)