Question

I am using gazebo_ros_depth_camera to generate a point cloud with Gazebo 1.9.2, ROS Hydro, and Ubuntu 12.04 LTS. Here is the relevant section of my URDF file:

<gazebo reference="bottom_mast_camera">
  <sensor name="bottom_mast_camera" type="depth">
    <always_on>true</always_on>
    <update_rate>${mast_cam_frame_rate}</update_rate>

    <camera>
      <horizontal_fov>${mast_cam_h_fov}</horizontal_fov>
      <image>
        <width>${mast_cam_img_width}</width>
        <height>${mast_cam_img_height}</height>
        <format>R8G8B8</format>
      </image>
      <clip>
        <near>${mast_cam_near_clip}</near>
        <far>${mast_cam_far_clip}</far>
      </clip>
      <depth_camera>
        <output>points</output>
      </depth_camera>
    </camera>

    <plugin name="bottom_mast_depth_camera"
            filename="libgazebo_ros_depth_camera.so">
      <cameraName>bottom_mast_camera</cameraName>
      <frameName>bottom_mast_camera_frame</frameName>
      <updateRate>${mast_cam_frame_rate}</updateRate>
      <pointCloudCutoff>2.0</pointCloudCutoff>
    </plugin>
  </sensor>
</gazebo>

Notice that I am using "points" in the <output> element, not "depths". Is such a point cloud supposed to be a color point cloud? I found the Gazebo source code that creates the point cloud, and it is producing a color point cloud. However, when I subscribe to the cloud on a ROS topic, the green and blue values are always zero. Red is usually 128 or 160. <output>depths</output> results in a correct color point cloud.

Asked by Jim Rothrock on 2014-02-11 13:28:02 UTC

Answer 1

I have a strong suspicion that this is a bug based on a similar experience I had. Here is the issue I opened to bring up the problem:

https://bitbucket.org/osrf/gazebo/issues/1865/rendering-depthcamera-does-not-output

The reason that it works for "depths" and not for "points" is because a Gazebo developer came across the bug when writing the gazebo_ros_depth_camera plugin. Because of this bug, he had to write a computationally expensive workaround that indirectly calculates the RGB point cloud from the depth image. If you set the to "points" in the SDF, the gazebo_ros_depth_camera plugin instead uses an incomplete part of the developer's code, which still has the RGB color bug present.

Also FYI, the two hexadecimal values I list in the bug report correspond to the 128 and 160 values you found for the red channel.

Asked by pcdangio on 2016-03-01 00:48:50 UTC

Does gazebo_ros_depth_camera with "points" output produce a color point cloud?

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