Adds option for terrain border to above or below the ground (#2394)

# Description

Adds option to add terrain border as "wall" above the ground or as
terrain extension below the ground in `TerrainGeneratorCfg`.

## Type of change

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

## Checklist

- [x] 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
- [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: Kelly Guo <kellyg@nvidia.com>
Signed-off-by: Kelly Guo <kellyguo123@hotmail.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyguo123@hotmail.com>

source/isaaclab/config/extension.toml

 [package]
 
 # Note: Semantic Versioning is used: https://semver.org/
-version = "0.39.2"
+version = "0.39.4"
 
 # Description
 title = "Isaac Lab framework for Robot Learning"

source/isaaclab/docs/CHANGELOG.rst

 Changelog
 ---------
 
+0.39.4 (2025-05-16)
+~~~~~~~~~~~~~~~~~~~
+
+Fixed
+^^^^^
+
+* Fixed penetration issue for negative border height in :class:`~isaaclab.terrains.terrain_generator.TerrainGeneratorCfg`.
+
+
 0.39.3 (2025-05-16)
 ~~~~~~~~~~~~~~~~~~~
 

source/isaaclab/isaaclab/terrains/terrain_generator.py

@@ -271,7 +271,7 @@ class TerrainGenerator:
             -self.cfg.border_height / 2,
         )
         # border mesh
-        border_meshes = make_border(border_size, inner_size, height=self.cfg.border_height, position=border_center)
+        border_meshes = make_border(border_size, inner_size, height=abs(self.cfg.border_height), position=border_center)
         border = trimesh.util.concatenate(border_meshes)
         # update the faces to have minimal triangles
         selector = ~(np.asarray(border.triangles)[:, :, 2] < -0.1).any(1)

source/isaaclab/isaaclab/terrains/terrain_generator_cfg.py

@@ -136,7 +136,11 @@ class TerrainGeneratorCfg:
     """The width of the border around the terrain (in m). Defaults to 0.0."""
 
     border_height: float = 1.0
-    """The height of the border around the terrain (in m). Defaults to 1.0."""
+    """The height of the border around the terrain (in m). Defaults to 1.0.
+
+    .. note::
+      The default border extends below the ground. If you want to make the border above the ground, choose a negative value.
+    """
 
     num_rows: int = 1
     """Number of rows of sub-terrains to generate. Defaults to 1."""