Inertial <pose relative_to="some_frame"> has no effect

[sloretz]

I'm unable to get the pose of an <inertial> relative to a frame using sdformat9. It looks like the relative_to attribute has no effect if used in the <pose> of an <inertial>. The pose is always treated as if it were in link frame.

<?xml version='1.0' encoding='utf-8'?>
<sdf version="1.7">
  <model name="pose_inertial_in_frame">
    <frame name="some_frame">
      <pose>0 0 1 0 0 0</pose>-->
    </frame>
    <link name="pose_inertial_in_frame_link">
      <visual name="pose_inertial_in_frame_link_visual">
        <pose relative_to="some_frame">0 0 0 0 0 0</pose>
        <geometry>
          <box>
            <size>0.1 0.2 0.4</size>
          </box>
        </geometry>
      </visual>
      <collision name="pose_inertial_in_frame_link_collision">
        <pose relative_to="some_frame">0 0 0 0 0 0</pose>
        <geometry>
          <box>
            <size>0.1 0.2 0.4</size>
          </box>
        </geometry>
      </collision>
      <inertial>
        <pose relative_to="some_frame">0 0 0 0 0 0</pose>
        <mass>1.23</mass>
        <inertia>
          <ixx>0.0205</ixx>
          <ixy>0</ixy>
          <ixz>0</ixz>
          <iyy>0.017425</iyy>
          <iyz>0</iyz>
          <izz>0.005125</izz>
        </inertia>
      </inertial>
    </link>
  </model>
</sdf>

It looks like the inertial is in the wrong pose using gazebo 11.1.0. It should be at the same location as the visual and collision, but it's in the ground.

The SDFormat API doesn't have a SemanticPose() API for inertials. I was expecting the Inertial() API to return a pose in link frame, but with the relative_to frame resolved. It looks like the issue is a variable inertialFrame is initialized, but never set with the true value: Edit: loadPose sets the variable inertiaFrame, but then it's not used anywhere after that.

https://github.com/osrf/sdformat/blob/b6c761ba38652ea440c4f728d60ef4b85cebf511/src/Link.cc#L169-L177

https://github.com/osrf/sdformat/blob/b6c761ba38652ea440c4f728d60ef4b85cebf511/src/Link.cc#L204-L205

[EricCousineau-TRI]

EDIT: Ignore this suggestion. It's bad.

This is feasible for libsdformat11 milestone:

• Add Link::ResolveInertial(relative_to="")
• Deprecate Link::Inertial()
• Replace with explicit Link::RawInertial()

Alternative:

• Fail fast if //inertial/pose/relative_to is non-default

[EricCousineau-TRI]

Per f2f, would be simplest to error out if //inertial/pose/@relative_to is non-default.

It's probably a niche case to have that and //link/pose/@relative_to differ (creds to @sammy-tri)