Merge pull request #207 from ami-iit/fix_default_terrain_normal

Fix default normal of plane terrain

src/jaxsim/terrain/terrain.py

@@ -73,7 +73,7 @@ def __eq__(self, other: FlatTerrain) -> bool:
 class PlaneTerrain(FlatTerrain):
 
     plane_normal: tuple[float, float, float] = jax_dataclasses.field(
-        default=(0.0, 0.0, 0.0), kw_only=True
+        default=(0.0, 0.0, 1.0), kw_only=True
     )
 
     @staticmethod