Clarifies asset classes' default_inertia tensor coordinate frame

CONTRIBUTORS.md

@@ -111,6 +111,7 @@ Guidelines for modifications:
 * Özhan Özen
 * Patrick Yin
 * Peter Du
+* Philipp Reist
 * Pulkit Goyal
 * Qian Wan
 * Qinxi Yu

source/isaaclab/isaaclab/assets/articulation/articulation_data.py

@@ -151,8 +151,9 @@ def update(self, dt: float):
     default_inertia: torch.Tensor = None
     """Default inertia for all the bodies in the articulation. Shape is (num_instances, num_bodies, 9).
 
-    The inertia is the inertia tensor relative to the center of mass frame. The values are stored in
-    the order :math:`[I_{xx}, I_{xy}, I_{xz}, I_{yx}, I_{yy}, I_{yz}, I_{zx}, I_{zy}, I_{zz}]`.
+    The inertia tensor should be given with respect to the center of mass, expressed in the articulation links' actor frame.
+    The values are stored in the order :math:`[I_{xx}, I_{yx}, I_{zx}, I_{xy}, I_{yy}, I_{zy}, I_{xz}, I_{yz}, I_{zz}]`.
+    However, due to the symmetry of inertia tensors, row- and column-major orders are equivalent.
 
     This quantity is parsed from the USD schema at the time of initialization.
     """

source/isaaclab/isaaclab/assets/rigid_object/rigid_object_data.py

@@ -112,8 +112,11 @@ def update(self, dt: float):
     default_inertia: torch.Tensor = None
     """Default inertia tensor read from the simulation. Shape is (num_instances, 9).
 
-    The inertia is the inertia tensor relative to the center of mass frame. The values are stored in
-    the order :math:`[I_{xx}, I_{xy}, I_{xz}, I_{yx}, I_{yy}, I_{yz}, I_{zx}, I_{zy}, I_{zz}]`.
+    The inertia tensor should be given with respect to the center of mass, expressed in the rigid body's actor frame.
+    The values are stored in the order :math:`[I_{xx}, I_{yx}, I_{zx}, I_{xy}, I_{yy}, I_{zy}, I_{xz}, I_{yz}, I_{zz}]`.
+    However, due to the symmetry of inertia tensors, row- and column-major orders are equivalent.
+
+    This quantity is parsed from the USD schema at the time of initialization.
     """
 
     ##

source/isaaclab/isaaclab/assets/rigid_object_collection/rigid_object_collection_data.py

@@ -118,8 +118,11 @@ def update(self, dt: float):
     default_inertia: torch.Tensor = None
     """Default object inertia tensor read from the simulation. Shape is (num_instances, num_objects, 9).
 
-    The inertia is the inertia tensor relative to the center of mass frame. The values are stored in
-    the order :math:`[I_{xx}, I_{xy}, I_{xz}, I_{yx}, I_{yy}, I_{yz}, I_{zx}, I_{zy}, I_{zz}]`.
+    The inertia tensor should be given with respect to the center of mass, expressed in the rigid body's actor frame.
+    The values are stored in the order :math:`[I_{xx}, I_{yx}, I_{zx}, I_{xy}, I_{yy}, I_{zy}, I_{xz}, I_{yz}, I_{zz}]`.
+    However, due to the symmetry of inertia tensors, row- and column-major orders are equivalent.
+
+    This quantity is parsed from the USD schema at the time of initialization.
     """
 
     ##