Supports setting the ground plane color using the terrain importer (#1791)

The default plane configuration supports setting the plane color, but
this option is not currently exposed via the terrain importer. This PR
adds a ``color'' field to the terrain importer that is only used for
configuring a plane.

- New feature (non-breaking change which adds functionality)

<img width="912" alt="image"
src="https://github.com/user-attachments/assets/4e509270-a953-49e8-88e7-b67bc1a92d2c"
/>

<img width="909" alt="image"
src="https://github.com/user-attachments/assets/0aa77530-befe-4c30-991d-e668561b9793"
/>

Configuration:

```python
terrain = TerrainImporterCfg(
            prim_path="/World/ground",
            terrain_type="plane",
            terrain_generator=None,
            max_init_terrain_level=None,
            collision_group=-1,
            physics_material=sim_utils.RigidBodyMaterialCfg(
                friction_combine_mode="multiply",
                restitution_combine_mode="multiply",
                static_friction=1.0,
                dynamic_friction=1.0,
            ),
            color=(1.0, 0.0, 0.0), # Red
            debug_vis=False,
        )
```

- [ ] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [ ] I have made corresponding changes to the documentation
- [X] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] 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: Kyle Morgenstein <34984693+KyleM73@users.noreply.github.com>
Signed-off-by: Mayank Mittal <12863862+Mayankm96@users.noreply.github.com>
Co-authored-by: Mayank Mittal <12863862+Mayankm96@users.noreply.github.com>

source/isaaclab/isaaclab/terrains/terrain_importer.py

@@ -10,6 +10,7 @@ import torch
 import trimesh
 from typing import TYPE_CHECKING
 
+import omni.log
 import warp
 from pxr import UsdGeom
 
@@ -196,9 +197,21 @@ class TerrainImporter:
         # create a warp mesh
         device = "cuda" if "cuda" in self.device else "cpu"
         self.warp_meshes[key] = convert_to_warp_mesh(mesh.vertices, mesh.faces, device=device)
+        # obtain ground plane color from the configured visual material
+        color = (0.0, 0.0, 0.0)
+        if self.cfg.visual_material is not None:
+            material = self.cfg.visual_material.to_dict()
+            # defaults to the `GroundPlaneCfg` color if diffuse color attribute is not found
+            if "diffuse_color" in material:
+                color = material["diffuse_color"]
+            else:
+                omni.log.warn(
+                    "Visual material specified for ground plane but no diffuse color found."
+                    " Using default color: (0.0, 0.0, 0.0)"
+                )
 
         # get the mesh
-        ground_plane_cfg = sim_utils.GroundPlaneCfg(physics_material=self.cfg.physics_material, size=size)
+        ground_plane_cfg = sim_utils.GroundPlaneCfg(physics_material=self.cfg.physics_material, size=size, color=color)
         ground_plane_cfg.func(self.cfg.prim_path, ground_plane_cfg)
 
     def import_mesh(self, key: str, mesh: trimesh.Trimesh):

source/isaaclab/isaaclab/terrains/terrain_importer_cfg.py

@@ -65,7 +65,7 @@ class TerrainImporterCfg:
     """The spacing between environment origins when defined in a grid. Defaults to None.
 
     Note:
-      This parameter is used only when the ``terrain_type`` is ``"plane"`` or ``"usd"``.
+      This parameter is used only when the ``terrain_type`` is "plane" or "usd".
     """
 
     visual_material: sim_utils.VisualMaterialCfg | None = sim_utils.PreviewSurfaceCfg(
@@ -73,10 +73,12 @@ class TerrainImporterCfg:
     )
     """The visual material of the terrain. Defaults to a dark gray color material.
 
-    The material is created at the path: ``{prim_path}/visualMaterial``. If `None`, then no material is created.
+    This parameter is used for both the "generator" and "plane" terrains.
 
-    .. note::
-        This parameter is used only when the ``terrain_type`` is ``"generator"``.
+    - If the ``terrain_type`` is "generator", then the material is created at the path
+      ``{prim_path}/visualMaterial`` and applied to all the sub-terrains.
+    - If the ``terrain_type`` is "plane", then the diffuse color of the material is set to
+      to the grid color of the imported ground plane.
     """
 
     physics_material: sim_utils.RigidBodyMaterialCfg = sim_utils.RigidBodyMaterialCfg()
@@ -85,7 +87,7 @@ class TerrainImporterCfg:
     The material is created at the path: ``{prim_path}/physicsMaterial``.
 
     .. note::
-        This parameter is used only when the ``terrain_type`` is ``"generator"`` or ``"plane"``.
+        This parameter is used only when the ``terrain_type`` is "generator" or "plane".
     """
 
     max_init_terrain_level: int | None = None

source/isaaclab/test/terrains/test_terrain_importer.py

@@ -26,7 +26,7 @@ from isaacsim.core.prims import RigidPrim, SingleGeometryPrim, SingleRigidPrim
 from isaacsim.core.utils.extensions import enable_extension
 
 import isaaclab.terrains as terrain_gen
-from isaaclab.sim import SimulationContext, build_simulation_context
+from isaaclab.sim import PreviewSurfaceCfg, SimulationContext, build_simulation_context
 from isaaclab.terrains import TerrainImporter, TerrainImporterCfg
 from isaaclab.terrains.config.rough import ROUGH_TERRAINS_CFG
 from isaaclab.utils.assets import ISAAC_NUCLEUS_DIR
@@ -101,18 +101,22 @@ class TestTerrainImporter(unittest.TestCase):
     def test_plane(self) -> None:
         """Generates a plane and tests that the resulting mesh has the correct size."""
         for device in ("cuda:0", "cpu"):
+            for use_custom_material in [True, False]:
                 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
                     terrain_importer_cfg = terrain_gen.TerrainImporterCfg(
                         prim_path="/World/ground",
                         terrain_type="plane",
                         num_envs=1,
                         env_spacing=1.0,
+                        visual_material=visual_material,
                     )
                     terrain_importer = TerrainImporter(terrain_importer_cfg)