Add custom point cloud frame ID support to Depth and RGBD camera sensors

[david-wb]

🎉 New feature

Closes #488

Summary

The problem
Currently, the depth and rgbd cameras use the content from the <frame_id> tag or the default frameId for both the
the images and the point cloud. However, the images typically need an optical frame id while the point cloud needs a "sensor" frame id.

The Solution
This proposed change enables depth and rbgd camera sensors to include a new <points_frame_id> tag to use for the point cloud messages. This is not a breaking change, because when the tag is not included, behavior is unchanged.

Example:

      <sensor name="camera_with_points_frame_id" type="depth">
        <update_rate>10</update_rate>
        <frame_id>optical_frame</frame_id>
        <points_frame_id>points_frame</points_frame_id>
        <topic>/camera2/image</topic>
        <camera>
          <horizontal_fov>1.0472</horizontal_fov>
          <image>
            <width>1000</width>
            <height>1000</height>
          </image>
          <lens>
            <projection>
              <p_fx>866.23</p_fx>
              <p_fy>866.23</p_fy>
              <p_cx>500</p_cx>
              <p_cy>500</p_cy>
              <tx>300</tx>
              <ty>200</ty>
            </projection>
          </lens>
        </camera>
      </sensor>

Test it

To test manually, launch gazebo sim with a urdf containing a depth camera that uses the new tag. Then verify frame ids on the images and point clouds are correct.

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)
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[iche033]

my understanding from going over #488 again is that a separate frame id field is not desired for reasons mentioned in #488 (comment) - mainly that the separate frame is needed by ROS and so that frame should be created in ros_gz. I started the work on this in gazebosim/ros_gz#703 but haven't had the chance to get back to it.

[roncapat]

Only one frame is needed on ROS side IMHO.

[david-wb]

@iche033 ros_gz_bridge is meant to be a translation layer and should not worry about this frame id detail. The optical and sensor frames are not the same, and it should be possible to specify both in the depth and rgbd sensor sdf. So I respectfully disagree with comment #488, but this PR is just a proposed solution. No problem if you choose to do it another way, I just hope the issue is resolved. Thanks for reviewing.

[iche033]

Ok I don't want to go back and forth between different solutions to the optical frame problem as that caused other complaints before. If you're ok with any solution and just want the problem resolved, I just updated gazebosim/ros_gz#703 - Would you able to give that PR a try?