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VRPN Mocap ROS 2 Bridge

This page explains how to use the vrpn_mocap bridge to publish tracked pose, twist, and acceleration as ROS topics:

  1. How to connect ROS 2 to the Vicon system through VRPN.
  2. How to isolate a robot and laptop on a shared Wi-Fi network using a custom ROS domain.

1. Overview

Once the Vicon PC runs and successfully tracks one or more objects, as explained in Vicon Motion Capture, a tracked object named <tracker_name> is published as:

  • /vrpn_mocap/<tracker_name>/pose
  • /vrpn_mocap/<tracker_name>/twist
  • /vrpn_mocap/<tracker_name>/accel

2. Installing vrpn_mocap from binary release

On Ubuntu with ROS 2:

sudo apt install ros-<rosdistro>-vrpn-mocap

3. Starting the VRPN client

After sourcing ROS2, run:

ros2 launch vrpn_mocap client.launch.yaml server:=192.168.0.232 port:=3883

Assuming 192.168.0.232 is the IP adress of the of the Vicon PC, as explained in Network, and 3883 the port.

All actively tracked objects on the Vicon PC will now be published as:

  • /vrpn_mocap/<tracker_name>/pose
  • /vrpn_mocap/<tracker_name>/twist
  • /vrpn_mocap/<tracker_name>/accel

Where <tracker_name> is the object's name on the Vicon PC. After starting, you can verify topics appear using:

ros2 topic list | grep vrpn

3.1 Parameters

Useful launch arguments may be:

  • update_freq (double) – frequency at which tracked object topics are published, default value is 100. In some cases, for example when recording a rosbag, it may be useful to reduce this.
  • frame_id (string) – frame name of the fixed world frame (default: "world")
  • sensor_data_qos – use best-effort QoS for the VRPN data stream; set to false to use the system default QoS, which is reliable (default: true)
  • use_vrpn_timestamps (bool) – use timestamps coming from VRPN. This ensures that the interval between frame timestamps is not modified (default: false)

Example:

ros2 launch vrpn_mocap client.launch.yaml server:=192.168.0.232 port:=3883 update_freq:=15.0

A more detailed explanation of parameters and the default launch file is provided at https://docs.ros.org/en/humble/p/vrpn_mocap/index.html.

A more detailed explanation of parameters and the default launch file is provided at https://docs.ros.org/en/humble/p/vrpn_mocap/index.html.

4. ROS domain setup on MRL Wi-Fi network

When multiple people use ROS 2 on the same Wi-Fi network, topics may be shared across all users on the LAN. Set a ROS_DOMAIN_ID to specify which devices should be able to discover each other. For example, when using:

  • a robot
  • a laptop

Run, in every terminal on both devices:

export ROS_DOMAIN_ID=42

To set the domain id to 42. You can also add this to ~/.bashrc on both devices.

4.1 Troubleshooting

Setting up the domain ID can be a hassle. Consult https://docs.ros.org/en/eloquent/Tutorials/Configuring-ROS2-Environment.html for more information. Alternatively, use ChatGPT for troubleshooting. Two or three points that may be worth considering, at your own risk, are:

  • Restarting the ROS background service on the robot when topics are not visible, e.g. with sudo systemctl restart mirte-ros
  • Ensuring ROS_LOCALHOST_ONLY is set to inactive (0 instead of 1) using: export ROS_LOCALHOST_ONLY=0
  • Restarting the daemon on your PC with ros2 daemon stop and then ros2 daemon start

5. Acknowledgement

The VRPN client was developed by a third party and is publicly available via https://github.com/vrpn/vrpn.