[Question] How do I rescale a primitive upon reset along with it's collision mesh?

[aaronrockmenezes]

Question

Hi, I've been trying to non-uniformly rescale my primitives at runtime using the function below:

def randomize_shape_scale(self,
                          prim_path_expr: str | list,
                          is_random: bool = True):
    world = World.instance()
    if world.is_playing():
        world.pause()

    stage = get_current_stage()

    # Resolve paths
    if isinstance(prim_path_expr, str):
        prim_paths = sim_utils.find_matching_prim_paths(prim_path_expr)
    elif isinstance(prim_path_expr, list):
        prim_paths = []
        for expr in prim_path_expr:
            prim_paths.extend(sim_utils.find_matching_prim_paths(expr))

    print(
        f"\n[Randomizing Xform Scale Only] Processing {len(prim_paths)} objects..."
    )
    obj_configs = list(self.cfg.vpt_objects.rigid_objects.values())
    bbox_cache = UsdGeom.BBoxCache(Usd.TimeCode.Default(),
                                   [UsdGeom.Tokens.default_])

    with Sdf.ChangeBlock():
        for prim_path in prim_paths:
            # Only process obs_* prims
            if "/obs_" not in prim_path:
                continue

            root_prim = stage.GetPrimAtPath(prim_path)
            if not root_prim.IsValid():
                continue

            # Parse indices
            try:
                path_str = root_prim.GetPath().pathString
                path_parts = path_str.split("/")
                env_part = next(p for p in path_parts
                                if p.startswith("env_"))
                env_idx = int(env_part.split("_")[-1])
                obs_part = next(p for p in path_parts
                                if p.startswith("obs_"))
                obj_idx = int(obs_part.split("_")[-1])
            except:
                continue

            if obj_idx >= len(obj_configs):
                continue

            obj_cfg = obj_configs[obj_idx]
            spawn_cfg = obj_cfg.spawn

            # Get/Create Xform ops
            xform = UsdGeom.Xformable(root_prim)
            scale_op = None
            translate_op = None

            for op in xform.GetOrderedXformOps():
                if op.GetOpType() == UsdGeom.XformOp.TypeScale:
                    scale_op = op
                elif op.GetOpType() == UsdGeom.XformOp.TypeTranslate:
                    translate_op = op

            if scale_op is None:
                scale_op = xform.AddScaleOp(
                    UsdGeom.XformOp.PrecisionDouble)
            if translate_op is None:
                translate_op = xform.AddTranslateOp(
                    UsdGeom.XformOp.PrecisionDouble)

            if is_random:
                base_dim = self.vpt_base_dims[obj_idx].cpu().numpy()
                final_scale_vec = Gf.Vec3d(1, 1, 1)
                final_z_pos = 0.0
                z_offset_multiplier = 0.0
                shape_name = -1

                # Determine scale based on object type
                if isinstance(spawn_cfg, sim_utils.UsdFileCfg):
                    filename = spawn_cfg.usd_path.split("/")[-1].split(
                        ".")[0]
                    if filename.endswith('X'):
                        shape_name = 0
                        s_xz = random.uniform(0.5, 2.5)
                        s_y = random.uniform(0.5, 2.5)
                        final_scale_vec = Gf.Vec3d(s_xz, s_y, s_xz)
                    elif filename.endswith('L'):
                        shape_name = 1
                        s_factor = random.uniform(0.5, 2.5)
                        final_scale_vec = Gf.Vec3d(s_factor, s_factor,
                                                   s_factor)
                    else:
                        s_xy = random.uniform(0.5, 2.5)
                        s_z = random.uniform(0.5, 2.5)
                        final_scale_vec = Gf.Vec3d(s_xy, s_xy, s_z)

                elif isinstance(spawn_cfg, sim_utils.MeshCuboidCfg):
                    shape_name = 2
                    z_offset_multiplier = 0.5
                    s_x = random.uniform(0.5, 2.5)
                    s_y = random.uniform(0.5, 2.5)
                    s_z = random.uniform(0.5, 2.5)
                    final_scale_vec = Gf.Vec3d(s_x, s_y, s_z)
                    final_z_pos = base_dim[2] * s_z * z_offset_multiplier

                elif isinstance(
                        spawn_cfg,
                    (sim_utils.MeshCylinderCfg, sim_utils.MeshConeCfg)):
                    shape_name = 3 if isinstance(
                        spawn_cfg, sim_utils.MeshCylinderCfg) else 4
                    z_offset_multiplier = 0.5
                    s_r = random.uniform(0.75, 1.0)
                    s_h = random.uniform(0.75, 2.5)
                    final_scale_vec = Gf.Vec3d(s_r, s_r, s_h)
                    final_z_pos = base_dim[2] * s_h * z_offset_multiplier

                # Apply ONLY Xform transformations
                scale_op.Set(final_scale_vec)
                current_trans = translate_op.Get()
                translate_op.Set(
                    Gf.Vec3d(current_trans[0], current_trans[1],
                             final_z_pos))

                # Update internal state
                self.obj_default_state[env_idx, obj_idx,
                                           2] = final_z_pos
                self.z_offset_ratios[env_idx,
                                         obj_idx] = z_offset_multiplier
                self.shapes[env_idx, obj_idx] = shape_name

    world.play()
    self.sim.step(render=False)

I'm able to scale the visual material just fine, but my agent, a MeshCuboid that I control with the keyboard, just passes through the objects. I also see that some objects just float while others sink partially into the ground (see attached images).

All these obstacle objects are part of a RigidObjectCollection and I want to rescale them upon every reset.

Can someone help me out?

Build Info

• Isaac Lab Version: 0.45.7
• Isaac Sim Version: 5.0

[aaronrockmenezes]

[aaronrockmenezes]

Screencast.from.2026-01-30.15-48-21.mp4

[RandomOakForest]

Thank you for posting this and adding the video. Note that you may randomize your obstacle dimensions through the Isaac Lab spawn/config layer (MeshCuboidCfg.size, MeshCylinderCfg.height/radius, etc.) before creating or re‑creating the RigidObjectCollection at reset, and rely on reset/asset reconstruction rather than post‑spawn UsdGeom.Xform scaling to keep collisions consistent.

[aaronrockmenezes]

What I'm trying to achieve is to be able to rescale and recolor objects with every reset because destroying and recreating them is quite slow. I'm already hitting low FPS on my RL task 150 FPS with 96 environments with 2 tiled cameras each, 3072 objects total on a RTX TITAN; destroying and recreating the object would be much slower than rescaling during reset right?

[RandomOakForest]

Following up, apologies for the late reply. That is a good question I don't have an answer for. I will move this to our Discussions for follow up.