Gazebo plugins

tags: ros

• Gazebo plugins
  • Intro
  • Reference
  • General usage
  • List of common plugins
    • Differential Drive
    • Skid Steering Drive
    • Lidar
    • Camera
    • Depth camera (Microsoft Kinect)
    • Projector

Intro

• This is for Gazebo-classic.
• Users of Ubuntu 18.04+ could switch to Gazebo Garden for more advanced functionalities.

Gazebo plugins enables the simulation of models and sensors, such as drivers, cameras, lidars, etc. Aside from some common tags (ex: updateRate, visualize), different plugins have different custom parameters that could be configured.

Lists of available plugins could be found at the official Gazebo Tutorial.

Reference

• ros wiki - gazebo_plugins
• official Gazebo Tutorial - Gazebo plugins in ROS
• gazebo plugin source code - Github repo
• example of xacro files with lidar, (depth) camera, projector plugin - my Github repo (branch "gazebo-sensors")

General usage

In robot URDF, insert plugin inside the gazebo tag.

<robot>
    ......
    <gazebo>
        <plugin name="${name_of_plugin}" filename="${file_name_of_plugin}">
            ... plugin paameters ...
        </plugin>
    </gazebo>
    ......
</robot>

List of common plugins

Differential Drive

• plugin filename: libgazebo_ros_diff_drive.so
• suitable for driving 2-wheel robots
  • receive - motion command (geometry_msgs/Twist)
    –> <commandTopic> - topic name, default to 'cmd_vel'
    –> could be controlled with teleop mode
    rosrun teleop_twist_keyboard teleop_twist_keyboard.py
  • publish - transforms for wheel links & odometry, joint states of wheels
    

Skid Steering Drive

• plugin filename: libgazebo_ros_skid_steer_drive.so
• suitable for driving 4-wheel robots
  • receive - motion command (geometry_msgs/Twist)
    –> <topicName> default to 'cmd_vel'
  • publish - transforms & joint states of wheels
    –> <broadcastTF> - set true/false

Lidar

• plugin filename: libgazebo_ros_lidar.so

Camera

• plugin filenmae: libgazebo_ros_camera.so
• In order to transform from the ROS coordinate to the camera frame, it is recommended to define additional frame with a "_optical" suffix. (refer: REP 103)
• The joint between camera_link & camera_optical_link would be configured as

<origin xyz="0.0 0.0 0.0" rpy="-1.57 0.0 -1.57"

• example - camera.xacro
  • In the gazebo section, the camera's parameters, including the fov, width, height, format, far/near clip distance (deciding the shape of the frustrum), noise, could be configured
  • The gazebo reference would still be the camera_link, whereas the plugin frameName tag would be the camera_optical_link.

<!-- camera -->
<gazebo reference="mybot/camera_link">
    <material>Gazebo/Black</material>
    <sensor type="camera" name="camera1">
        <update_rate>30.0</update_rate>
        <visualize>true</visualize>
        <camera>
            <horizontal_fov>1.3962634</horizontal_fov>
            <image>
                <width>800</width>
                <height>800</height>
                <format>R8G8B8</format>
            </image>
            <clip>
                <near>0.02</near>
                <far>300</far>
            </clip>
            <noise>
                <type>gaussian</type>
                <!-- Noise is sampled independently per pixel on each frame.
                That pixel's noise value is added to each of its color
                channels, which at that point lie in the range [0,1]. -->
                <mean>0.0</mean>
                <stddev>0.007</stddev>
            </noise>
        </camera>

        <plugin name="camera_controller" filename="libgazebo_ros_camera.so">
            <cameraName>camera1</cameraName>
            <frameName>camera_optical_link</frameName>
        </plugin>
    </sensor>
</gazebo>

Depth camera (Microsoft Kinect)

• plugin filename: libgazebo_ros_openni_kinect.so
• similar to camera, except the sensor type would be "depth"
• publish
  • camera/depth/image: depth image
  • camera/image: RGB image
  • camera/depth/points (sensor_msgs/PointCloud2): the pointcloud that contains the 3d information
    • The color format need to be reconfigured in order to show correct color, or else the R & B would be messed up
    • This can be done by configuring the <format> (within <image>) from R8G8B8 to B8G8R8

Projector

• plugin filename: libgazebo_ros_projector.so
• Project static image in world.
• The <texture> tag would be the name of the image file.
  • The image should be put in folder /usr/share/gazebo-7/media/materials/textures. (see this thread). There also exist a couple of textures.
• Replace the <sensor> tag with <projector> tag.
• The projection would be in +Z direction.
• Projector parameters include
  • near_clip
  • far_clip
  • fov
    (Other tags seem to have no effect by far…)
    (<textureTopicName> & <projectorTopicName> not working as well…)