Callback based API for Implementing Custom Moment of Inertia Calculators for Meshes

[jasmeet0915]

🎉 New feature

Based on this proposal.

Note: This PR would require merging #1298 and #1299

Summary

• Added functions to register custom calculator and get custom calculator in ParserConfig.
• Added an InterfaceMoiCalculator class that can be used to send appropriate data to the calculator from sdformat.
• Added a <moi_calculator_params> tag that can be used to access custom calculator params from the SDF by using tags with namespaces. (See this for reference)
• Added MassMatrix() function to sdf::Mesh class and updated the Collision::MassMatrix() function to pass the parser config as well as sdf::ElementPtr to <moi_calculator_params> tag.

Demo & Usage Example

Demo 1: This demo shows the automatic inertia calculation feature on a rubber ducky model which is a non-convex mesh. On the left, we have the rubber ducky mesh with automatic calculations enabled and on the right, the mesh uses the default values.

Note: The inertial values are due to the scale of the mesh. You can see the banana for scale in between the 2 ducks. A density value for the duck was used which was calculated by using the mass and volume data of the duck found online.

Note: The voxel_size inertia param given in the snippet below is just for showing how the <auto_inertia_params> element could be used. This is not actually used by the calculator since we are not using a voxelization-based calculator.

SDF snippet for the duck mesh with auto inertial

<?xml version="1.0" ?>
<sdf version="1.6">
<model name="duck">
  <link name="duck_link">
    <pose>0 0 0 0 0 0</pose>
    <inertial auto="true" />
    <collision name="duck_collision">
    	<pose>0 0 0 0 0 0</pose>
      <density>111.8</density>
      <auto_inertia_params>
        <gz:voxel_size>0.01</gz:voxel_size>
      </auto_inertia_params>
      <geometry>
        <mesh>
          <uri>meshes/duck_collider.dae</uri>
        </mesh>
      </geometry>
    </collision>
    <visual name="duck_visual">
      <pose>0 0 0 0 0 0</pose>
      <geometry>
        <mesh>
          <uri>meshes/duck.dae</uri>
        </mesh>
      </geometry>
    </visual>
  </link>
  <static>true</static>
</model>
</sdf>

Demo 2: This demo shows 2 cylinders: One using a Collada cylinder mesh (right) and the other made using the <cylinder> geometry from SDF (left).

Both use <inertial auto="true" /> and we can see that the inertia values for both come up to be almost the same (within 0.005 tolerance). The mesh cylinder uses the mesh inertia calculator added to gz-sim and is used with libsdformat using the callback-based API.

SDF snippet for the mesh cylinder

  <model name="cylinder_dae">
    <pose>4 4 1 0 0 0</pose>
    <link name="cylinder_dae">
      <pose>0 0 0 0 0 0</pose>
      <inertial auto="false" />
      <collision name="cylinder_collision">
        <density>1240.0</density>
        <auto_inertia_params>
          <gz:voxel_size>0.01</gz:voxel_size>
        </auto_inertia_params>
        <geometry>
          <mesh>
            <uri>cylinder_dae/meshes/cylinder.dae</uri>
          </mesh>
        </geometry>
      </collision>
      <visual name="cylinder_visual">
        <pose>0 0 0 0 0 0</pose>
        <geometry>
          <mesh>
            <uri>cylinder_dae/meshes/cylinder.dae</uri>
          </mesh>
        </geometry>
      </visual>
    </link>
    <static>true</static>
  </model>

TODO:

• Update the nomenclature (interface class name, custom params tag name) to something more appropriate.
  • Rename <moi_calculator_params> to <auto_inertia_params>.
• Rename Mesh::MassMatrix() to Mesh::CalculateInertial() and change the return type to optional Inertial.
• Make mesh optional in CustomInertiaCalcProperties class as it might be extended in future for other types of shapes.
• Add //link/inertial/auto_inertia_params element in spec
• Update the SDFormat Proposal with an explanation of the API and add a basic example of using the API.
• Add Tests
• Add the functions to Python API

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

[azeey]

Looks great! Just a couple of comments

Feedback addressed