Adds check that no articulation root API is applied on rigid bodies (#1358)

# Description

If a USD contains an articulation root but we load it with a
`RigidObjectCfg` this would also load the articulation. This is
confusing as a user only expects a rigid body.

This PR adds a fix to ignore the articulation if a rigid body is
spawned.

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- Bug fix (non-breaking change which fixes an issue)

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## Checklist

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---------
Signed-off-by: lgulich <22480644+lgulich@users.noreply.github.com>
Signed-off-by: David Hoeller <dhoeller@nvidia.com>
Signed-off-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: David Hoeller <dhoeller@nvidia.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>

source/extensions/omni.isaac.lab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.27.21"
+version = "0.27.22"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/extensions/omni.isaac.lab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.27.22 (2024-12-06)
+~~~~~~~~~~~~~~~~~~~~
+
+Changed
+^^^^^^^
+
+* If a USD that contains an articulation root is loaded using a
+  :attr:`omni.isaac_lab.assets.RigidBody` we now fail unless the articulation root is explicitly
+  disabled. Using an articulation root for rigid bodies is not needed and decreases overall performance.
+
+
 0.27.21 (2024-12-06)
 ~~~~~~~~~~~~~~~~~~~
 

source/extensions/omni.isaac.lab/omni/isaac/lab/assets/rigid_object/rigid_object.py

@@ -291,6 +291,18 @@ class RigidObject(AssetBase):
                 " Please ensure that there is only one rigid body in the prim path tree."
             )
 
+        articulation_prims = sim_utils.get_all_matching_child_prims(
+            template_prim_path, predicate=lambda prim: prim.HasAPI(UsdPhysics.ArticulationRootAPI)
+        )
+        if len(articulation_prims) != 0:
+            if articulation_prims[0].GetAttribute("physxArticulation:articulationEnabled").Get():
+                raise RuntimeError(
+                    f"Found an articulation root when resolving '{self.cfg.prim_path}' for rigid objects. These are"
+                    f" located at: '{articulation_prims}' under '{template_prim_path}'. Please disable the articulation"
+                    " root in the USD or from code by setting the parameter"
+                    " 'ArticulationRootPropertiesCfg.articulation_enabled' to False in the spawn configuration."
+                )
+
         # resolve root prim back into regex expression
         root_prim_path = root_prims[0].GetPath().pathString
         root_prim_path_expr = self.cfg.prim_path + root_prim_path[len(template_prim_path) :]

source/extensions/omni.isaac.lab/test/assets/test_rigid_object.py

@@ -24,6 +24,7 @@ simulation_app = app_launcher.app
 import ctypes
 import torch
 import unittest
+from typing import Literal
 
 import omni.isaac.core.utils.prims as prim_utils
 
@@ -31,19 +32,23 @@ import omni.isaac.lab.sim as sim_utils
 from omni.isaac.lab.assets import RigidObject, RigidObjectCfg
 from omni.isaac.lab.sim import build_simulation_context
 from omni.isaac.lab.sim.spawners import materials
-from omni.isaac.lab.utils.assets import ISAAC_NUCLEUS_DIR
+from omni.isaac.lab.utils.assets import ISAAC_NUCLEUS_DIR, ISAACLAB_NUCLEUS_DIR
 from omni.isaac.lab.utils.math import default_orientation, random_orientation
 
 
 def generate_cubes_scene(
-    num_cubes: int = 1, height=1.0, has_api: bool = True, kinematic_enabled: bool = False, device: str = "cuda:0"
+    num_cubes: int = 1,
+    height=1.0,
+    api: Literal["none", "rigid_body", "articulation_root"] = "rigid_body",
+    kinematic_enabled: bool = False,
+    device: str = "cuda:0",
 ) -> tuple[RigidObject, torch.Tensor]:
     """Generate a scene with the provided number of cubes.
 
     Args:
         num_cubes: Number of cubes to generate.
         height: Height of the cubes.
-        has_api: Whether the cubes have a rigid body API on them.
+        api: The type of API that the cubes should have.
         kinematic_enabled: Whether the cubes are kinematic.
         device: Device to use for the simulation.
 
@@ -57,17 +62,25 @@ def generate_cubes_scene(
         prim_utils.create_prim(f"/World/Table_{i}", "Xform", translation=origin)
 
     # Resolve spawn configuration
-    if has_api:
-        spawn_cfg = sim_utils.UsdFileCfg(
-            usd_path=f"{ISAAC_NUCLEUS_DIR}/Props/Blocks/DexCube/dex_cube_instanceable.usd",
-            rigid_props=sim_utils.RigidBodyPropertiesCfg(kinematic_enabled=kinematic_enabled),
-        )
-    else:
+    if api == "none":
         # since no rigid body properties defined, this is just a static collider
         spawn_cfg = sim_utils.CuboidCfg(
             size=(0.1, 0.1, 0.1),
             collision_props=sim_utils.CollisionPropertiesCfg(),
         )
+    elif api == "rigid_body":
+        spawn_cfg = sim_utils.UsdFileCfg(
+            usd_path=f"{ISAAC_NUCLEUS_DIR}/Props/Blocks/DexCube/dex_cube_instanceable.usd",
+            rigid_props=sim_utils.RigidBodyPropertiesCfg(kinematic_enabled=kinematic_enabled),
+        )
+    elif api == "articulation_root":
+        spawn_cfg = sim_utils.UsdFileCfg(
+            usd_path=f"{ISAACLAB_NUCLEUS_DIR}/Tests/RigidObject/Cube/dex_cube_instanceable_with_articulation_root.usd",
+            rigid_props=sim_utils.RigidBodyPropertiesCfg(kinematic_enabled=kinematic_enabled),
+        )
+    else:
+        raise ValueError(f"Unknown api: {api}")
+
     # Create rigid object
     cube_object_cfg = RigidObjectCfg(
         prim_path="/World/Table_.*/Object",
@@ -161,7 +174,27 @@ class TestRigidObject(unittest.TestCase):
                 with self.subTest(num_cubes=num_cubes, device=device):
                     with build_simulation_context(device=device, auto_add_lighting=True) as sim:
                         # Generate cubes scene
-                        cube_object, _ = generate_cubes_scene(num_cubes=num_cubes, has_api=False, device=device)
+                        cube_object, _ = generate_cubes_scene(num_cubes=num_cubes, api="none", device=device)
+
+                        # Check that boundedness of rigid object is correct
+                        self.assertEqual(ctypes.c_long.from_address(id(cube_object)).value, 1)
+
+                        # Play sim
+                        sim.reset()
+
+                        # Check if object is initialized
+                        self.assertFalse(cube_object.is_initialized)
+
+    def test_initialization_with_articulation_root(self):
+        """Test that initialization fails when an articulation root is found at the provided prim path."""
+        for num_cubes in (1, 2):
+            for device in ("cuda:0", "cpu"):
+                with self.subTest(num_cubes=num_cubes, device=device):
+                    with build_simulation_context(device=device, auto_add_lighting=True) as sim:
+                        # Generate cubes scene
+                        cube_object, _ = generate_cubes_scene(
+                            num_cubes=num_cubes, api="articulation_root", device=device
+                        )
 
                         # Check that boundedness of rigid object is correct
                         self.assertEqual(ctypes.c_long.from_address(id(cube_object)).value, 1)