How do I integrate webots sensor plugins into a ros2 URDF/Xacro file?

Question

I am trying to set up a Lidar, IMU, and depth camera in Webots on a ROS 2 robot in its xacro file (starting with just the Lidar).

I currently have the following:

<webots>

  <plugin type="webots_ros2_driver::Ros2Lidar">
    <frameName>laser_frame</frameName>
    <enabled>true</enabled>
    <scanRate>10</scanRate>
    <topicName>/scan</topicName>
    <alwaysOn>true</alwaysOn>
  </plugin>

  <plugin type="webots_ros2_control::Ros2Control"/>

</webots>

I'm not sure about the parameters since I just adapted it from the IMU plugin from the turtlebot webots_ros2 example. But the only error I have is this:

[driver-2] ModuleNotFoundError: No module named 'webots_ros2_driver::Ros2Lidar'
[driver-2] terminate called after throwing an instance of 'std::runtime_error'
[driver-2]   what():  The webots_ros2_driver::Ros2Lidar plugin cannot be found (C++ or Python).

I've found the Ros2Lidar plugin locally (I think), but it doesn't seem to be able to find it. The demos all work, but the vast majority are just from robots built IN Webots .proto files. But I need to use ROS for the robot itself that uses a xacro file.

Any hints would be appreciated.

Thanks in advance, Craig

Answer 1

We are aware that there is a lack of documentation on current implemented device interfaces and how to use them. We are currently working on new tutorials for the official ROS 2 documentation.

Currently, there are 10 devices that have an automatic interface with ROS 2:

• Camera
• Compass
• Distance Sensor
• Emitter
• GPS
• LED
• Lidar
• Light Sensor
• Ranger Finder
• Receiver

For these devices, webots_ros2_driver will automatically load the static plugin. This means that associated topics and services will be created. You can have a look at each of these plugins in webots_ros2_driver/src/plugins/static. You can overwrite multiple parameters like topic names or the update rate in your URDF file in the <webots> tag. In your example, it would be:

<device reference="lidar_name_in_webots" type="Lidar">
  <ros>
    <frameName>laser_frame</frameName>
    <enabled>true</enabled>
    <scanRate>10</scanRate>
    <topicName>/scan</topicName>
    <alwaysOn>true</alwaysOn>
  </ros>
</device>    

There is also a plugin provided with webots_ros2_driver that interfaces IMU sensors. You can find it in webots_ros2_driver/src/plugins/dynamic. This plugin can be loaded in the exact way you did in your question:

<plugin type="webots_ros2_driver::Ros2IMU">
  <enabled>true</enabled>
  <topicName>/imu</topicName>
  <alwaysOn>true</alwaysOn>
  <frameName>imu_link</frameName>
  <inertialUnitName>inertial unit</inertialUnitName>
  <gyroName>gyro</gyroName>
</plugin>

If the default interfaces don't suit you or is not enough, you can create your own custom plugin. Please take a look at the following links to do so in C++ or Python: Tutorial-Creating-a-Custom-Cpp-Plugin and Tutorial-Creating-a-Custom-Python-Plugin.