Save normalising transform applied to mesh assets in mjModel.mesh_{pos,quat}

Fixes #409

PiperOrigin-RevId: 564217402
Change-Id: I53ddeef4e343905021cd7852d548f6769c876474

doc/XMLreference.rst

@@ -1439,16 +1439,16 @@ Positioning and orienting is complicated by the fact that vertex data are often
 whose origin is not inside the mesh. In contrast, MuJoCo expects the origin of a geom's local frame to coincide with the
 geometric center of the shape. We resolve this discrepancy by pre-processing the mesh in the compiler, so that it is
 centered around (0,0,0) and its principal axes of inertia are the coordinate axes. We also save the translation and
-rotation offsets needed to achieve such alignment. These offsets are then applied to the referencing geom's position and
-orientation; see also :at:`mesh` attribute of :ref:`geom <body-geom>` below. Fortunately most meshes used in robot
-models are designed in a coordinate frame centered at the joint. This makes the corresponding MJCF model intuitive: we
-set the body frame at the joint, so that the joint position is (0,0,0) in the body frame, and simply reference the mesh.
-Below is an MJCF model fragment of a forearm, containing all the information needed to put the mesh where one would
-expect it to be. The body position is specified relative to the parent body, namely the upper arm (not shown). It is
-offset by 35 cm which is the typical length of the human upper arm. If the mesh vertex data were not designed in the
-above convention, we would have to use the geom position and orientation (or the new refpos, refquat mechanism) to
-compensate, but in practice this is rarely needed.
-
+rotation offsets needed to achieve such alignment in :ref:`mjModel.mesh_pos<mjModel>` and
+:ref:`mjModel.mesh_quat<mjModel>`. These offsets are then applied to the referencing geom's position and orientation; see
+also :at:`mesh` attribute of :ref:`geom <body-geom>` below. Fortunately most meshes used in robot models are designed in
+a coordinate frame centered at the joint. This makes the corresponding MJCF model intuitive: we set the body frame at the
+joint, so that the joint position is (0,0,0) in the body frame, and simply reference the mesh. Below is an MJCF model
+fragment of a forearm, containing all the information needed to put the mesh where one would expect it to be. The body
+position is specified relative to the parent body, namely the upper arm (not shown). It is offset by 35 cm which is the
+typical length of the human upper arm. If the mesh vertex data were not designed in the above convention, we would have
+to use the geom position and orientation (or the new refpos, refquat mechanism) to compensate, but in practice this is
+rarely needed.
 .. code-block:: xml
 
    <asset>

doc/changelog.rst

@@ -64,17 +64,17 @@ General
     :ref:`integrators<option-integrator>` other than ``RK4``. See the flag documentation for more details.
 12. Added :ref:`ls_iterations<option-ls_iterations>` and :ref:`ls_tolerance<option-ls_tolerance>` options for adjusting
     linesearch stopping criteria in CG and Newton solvers. This can be useful for performance tuning.
-
+13. Added ``mesh_pos`` and ``mesh_quat`` fields to :ref:`mjModel` to store normalizing transformation.
 Python bindings
 ^^^^^^^^^^^^^^^
 
-13. Fixed `#870 <https://github.com/google-deepmind/mujoco/issues/870>`__ where calling ``update_scene`` with an invalid
+14. Fixed `#870 <https://github.com/google-deepmind/mujoco/issues/870>`__ where calling ``update_scene`` with an invalid
     camera name used the default camera.
 
 Bug fixes
 ^^^^^^^^^
 
-14. Fixed a bug that was causing the geom margins to be ignored during the midphase.
+15. Fixed a bug that was causing the geom margins to be ignored during the midphase.
 
 
 Version 2.3.7 (July 20, 2023)

doc/includes/references.h

@@ -1045,6 +1045,8 @@ struct mjModel_ {
   int*      mesh_texcoordadr;     // texcoord data address; -1: no texcoord   (nmesh x 1)
   int*      mesh_texcoordnum;     // number of texcoord                       (nmesh x 1)
   int*      mesh_graphadr;        // graph data address; -1: no graph         (nmesh x 1)
+  mjtNum*   mesh_pos;             // translation applied to asset vertices    (nmesh x 3)
+  mjtNum*   mesh_quat;            // rotation applied to asset vertices       (nmesh x 4)
   float*    mesh_vert;            // vertex positions for all meshes          (nmeshvert x 3)
   float*    mesh_normal;          // normals for all meshes                   (nmeshnormal x 3)
   float*    mesh_texcoord;        // vertex texcoords for all meshes          (nmeshtexcoord x 2)