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Mocap-PX4 Bridge

block diagram

This ROS 2 Package takes the Position and Orientation measurements from OptiTrack system and send them to PX4 through the uXRCE-DDS bridge between ROS 2 and PX4.

Complete Guideline

Please refer to this document for a complete guidline of using PX4 with OptiTrack.

Full block diagram

Pre conditions

Warning

Check that the OptiTrack 'Up axis' is the Z-axis, in Motive the default is Y-axis

This package assumes that the OptiTrack system is broadcasting the position and orientation of the robot with the following reference frame convention:

  • World frame: X axis Forward, Y-axis Left, Z-axis Up (Again: Check that the OptiTrack 'Up axis' is the Z-axis, in Motive the default is Y-axis).
  • Body frame: X axis Forward, Y-axis Left, Z-axis Up.

Getting started

We will create a ROS 2 workspace in ~/ros2_ws, clone the required packages, build, and run:

mkdir -p ~/ros2_ws/src/
cd ~/ros2_ws/src/
git clone https://github.com/ros-drivers/mocap_optitrack.git
git clone https://github.com/SaxionMechatronics/mocap_px4_bridge.git
git clone https://github.com/PX4/px4_msgs.git
cd ~/ros2_ws
colcon build --symlink-install
source ~/ros2_ws/install/setup.sh
ros2 launch mocap_px4_bridge run.launch.py

Changing the topics names

By default:

  1. This package will read the Optitrack measurements from the topic /Robot_1/pose
  2. Publish the measurements to the topic /fmu/in/vehicle_visual_odometry

To change the names of these topic, you need to edit the file config/params.yaml.

Transforming to PX4 reference frame convention

Assuming that:

  • P_opti is the position measurements from OptiTrack
  • P_px4 is the position sent to PX4
  • q_opti is the quaternion orientation measurements from OptiTrack
  • q_px4 is the quaternion sent to PX4. Here

Here is how the frame conversion is carried out:

P_px4.x =   P_optitrack.x​
P_px4.y = - P_optitrack.y​
P_px4.z = - P_optitrack.z​

q_px4.w =   q_px4.w​
q_px4.x =   q_px4.x ​
q_px4.y = - q_px4.y​
q_px4.z = - q_px4.z​

Acknowledgment

This training material was prepared and delivered as part of the Horizon Europe CSA project: AeroSTREAM (Grant Agreement number: 101071270).

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