Removes storage of meshes inside the TerrainImporter class (#1987)

# Description

Sometimes users want to import a USD file which doesn't have any
collider meshes. This MR allows having such USD files in the terrain
importer for visualization purposes.

Additionally, the MR removes the storage of warp and tri-mesh based
meshes inside the class. These are stored into the USD and are read
directly from there whenever needed. Their intended use-case for having
them inside the terrain class is not needed.

## Type of change

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

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [ ] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [x] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

---------
Signed-off-by: Mayank Mittal <12863862+Mayankm96@users.noreply.github.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>

source/isaaclab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.35.0"
+version = "0.36.0"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.36.0 (2025-03-07)
+~~~~~~~~~~~~~~~~~~~
+
+Removed
+^^^^^^^
+
+* Removed the storage of tri-meshes and warp meshes inside the :class:`~isaaclab.terrains.TerrainImporter` class.
+  Initially these meshes were added for ray-casting purposes. However, since the ray-caster reads the terrains
+  directly from the USD files, these meshes are no longer needed.
+* Deprecated the :attr:`warp_meshes` and :attr:`meshes` attributes from the
+  :class:`~isaaclab.terrains.TerrainImporter` class. These attributes now return an empty dictionary
+  with a deprecation warning.
+
+Changed
+^^^^^^^
+
+* Changed the prim path of the "plane" terrain inside the :class:`~isaaclab.terrains.TerrainImporter` class.
+  Earlier, the terrain was imported directly as the importer's prim path. Now, the terrain is imported as
+  ``{importer_prim_path}/{name}``, where ``name`` is the name of the terrain.
+
+
 0.35.0 (2025-03-07)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/terrains/__init__.py

@@ -11,11 +11,10 @@ There are two main components in this package:
   sub-terrain configuration. It creates a ``trimesh`` mesh object and contains the origins of
   each generated sub-terrain.
 * :class:`TerrainImporter`: This class mainly deals with importing terrains from different
-  possible sources and adding them to the simulator as a prim object. It also stores the
-  terrain mesh into a dictionary called :obj:`TerrainImporter.warp_meshes` that later can be used
-  for ray-casting. The following functions are available for importing terrains:
+  possible sources and adding them to the simulator as a prim object.
+  The following functions are available for importing terrains:
 
-  * :meth:`TerrainImporter.import_ground_plane`: spawn a grid plane which is default in isaacsim/isaaclab.
+  * :meth:`TerrainImporter.import_ground_plane`: spawn a grid plane which is default in Isaac Sim.
   * :meth:`TerrainImporter.import_mesh`: spawn a prim from a ``trimesh`` object.
   * :meth:`TerrainImporter.import_usd`: spawn a prim as reference to input USD file.
 

source/isaaclab/test/terrains/test_terrain_importer.py

@@ -14,7 +14,9 @@ simulation_app = AppLauncher(headless=True).app
 
 import numpy as np
 import torch
+import trimesh
 import unittest
+from typing import Literal
 
 import isaacsim.core.utils.prims as prim_utils
 import omni.kit
@@ -24,9 +26,10 @@ from isaacsim.core.api.objects import DynamicSphere
 from isaacsim.core.cloner import GridCloner
 from isaacsim.core.prims import RigidPrim, SingleGeometryPrim, SingleRigidPrim
 from isaacsim.core.utils.extensions import enable_extension
+from pxr import UsdGeom
 
 import isaaclab.terrains as terrain_gen
-from isaaclab.sim import PreviewSurfaceCfg, SimulationContext, build_simulation_context
+from isaaclab.sim import PreviewSurfaceCfg, SimulationContext, build_simulation_context, get_first_matching_child_prim
 from isaaclab.terrains import TerrainImporter, TerrainImporterCfg
 from isaaclab.terrains.config.rough import ROUGH_TERRAINS_CFG
 from isaaclab.utils.assets import ISAAC_NUCLEUS_DIR
@@ -81,8 +84,12 @@ class TestTerrainImporter(unittest.TestCase):
                 )
                 terrain_importer = TerrainImporter(terrain_importer_cfg)
 
-                # check mesh exists
-                mesh = terrain_importer.meshes["terrain"]
+                # check if mesh prim path exists
+                mesh_prim_path = terrain_importer.cfg.prim_path + "/terrain"
+                self.assertIn(mesh_prim_path, terrain_importer.terrain_prim_paths)
+
+                # obtain underling mesh
+                mesh = self._obtain_collision_mesh(mesh_prim_path, mesh_type="Mesh")
                 self.assertIsNotNone(mesh)
 
                 # calculate expected size from config
@@ -105,9 +112,6 @@ class TestTerrainImporter(unittest.TestCase):
                 with build_simulation_context(device=device, auto_add_lighting=True) as sim:
                     sim._app_control_on_stop_handle = None
 
-                    expectedSizeX = 2.0e6
-                    expectedSizeY = 2.0e6
-
                     # create custom material
                     visual_material = PreviewSurfaceCfg(diffuse_color=(1.0, 0.0, 0.0)) if use_custom_material else None
                     # Handler for terrains importing
@@ -120,16 +124,13 @@ class TestTerrainImporter(unittest.TestCase):
                     )
                     terrain_importer = TerrainImporter(terrain_importer_cfg)
 
-                    # check mesh exists
-                    mesh = terrain_importer.meshes["terrain"]
-                    self.assertIsNotNone(mesh)
-
-                    # get size from mesh bounds
-                    bounds = mesh.bounds
-                    actualSize = abs(bounds[1] - bounds[0])
+                    # check if mesh prim path exists
+                    mesh_prim_path = terrain_importer.cfg.prim_path + "/terrain"
+                    self.assertIn(mesh_prim_path, terrain_importer.terrain_prim_paths)
 
-                    self.assertAlmostEqual(actualSize[0], expectedSizeX)
-                    self.assertAlmostEqual(actualSize[1], expectedSizeY)
+                    # obtain underling mesh
+                    mesh = self._obtain_collision_mesh(mesh_prim_path, mesh_type="Plane")
+                    self.assertIsNone(mesh)
 
     def test_usd(self) -> None:
         """Imports terrain from a usd and tests that the resulting mesh has the correct size."""
@@ -146,8 +147,12 @@ class TestTerrainImporter(unittest.TestCase):
                 )
                 terrain_importer = TerrainImporter(terrain_importer_cfg)
 
-                # check mesh exists
-                mesh = terrain_importer.meshes["terrain"]
+                # check if mesh prim path exists
+                mesh_prim_path = terrain_importer.cfg.prim_path + "/terrain"
+                self.assertIn(mesh_prim_path, terrain_importer.terrain_prim_paths)
+
+                # obtain underling mesh
+                mesh = self._obtain_collision_mesh(mesh_prim_path, mesh_type="Mesh")
                 self.assertIsNotNone(mesh)
 
                 # expect values from USD file
@@ -226,6 +231,25 @@ class TestTerrainImporter(unittest.TestCase):
     Helper functions.
     """
 
+    def _obtain_collision_mesh(
+        self, mesh_prim_path: str, mesh_type: Literal["Mesh", "Plane"]
+    ) -> trimesh.Trimesh | None:
+        """Get the collision mesh from the terrain."""
+        # traverse the prim and get the collision mesh
+        mesh_prim = get_first_matching_child_prim(mesh_prim_path, lambda prim: prim.GetTypeName() == mesh_type)
+        # check it is valid
+        self.assertTrue(mesh_prim.IsValid())
+
+        if mesh_prim.GetTypeName() == "Mesh":
+            # cast into UsdGeomMesh
+            mesh_prim = UsdGeom.Mesh(mesh_prim)
+            # store the mesh
+            vertices = np.asarray(mesh_prim.GetPointsAttr().Get())
+            faces = np.asarray(mesh_prim.GetFaceVertexIndicesAttr().Get()).reshape(-1, 3)
+            return trimesh.Trimesh(vertices=vertices, faces=faces)
+        else:
+            return None
+
     @staticmethod
     def _obtain_grid_cloner_env_origins(num_envs: int, env_spacing: float, device: str) -> torch.Tensor:
         """Obtain the env origins generated by IsaacSim GridCloner (grid_cloner.py)."""