vrpn_client_node

vrpn_client_node is a ros node, used to obtain optitrack pose data /vrpn_client_node/RigidBody/pose. If Up Axis is set to Z Axis in motive, the pose data is in the ENU(X East, Y North, Z Up) or FLU(X Forward, Y Left, Z Up) coordinate system. This conforms to ROS conventions.

Usually the computer running vrpn_client_node and the computer running Motive software are under the same local area network (LAN). This vrpn_client_node has two potential uses:

• Use mavros to send to pixhawk by remapping topic /vrpn_client_node/RigidBody/pose to /mavros/vision_pose/pose. mavros is responsible for converting ENU to the NED(X North, Y East, Z Down) coordinate system used by PX4.

• Send directly to the USB device, and use the serial port to transmit the data to the microcontroller. The coordinate system needs to be transformed manually.

System Architecture:

• QGC or offboard control node running on the linux running machine.
• Companion computer is XU4. we can use raspberry pi instead of XU4. The mavros and vrpn_client_node running on Companion computer, so as the master node of ros.

Mocap computer settings

1. Align the UAV x-axis (forward direction) roughly with the x-axis of the optitrack system, select all marked points, and right-click to create a rigid body.

2. Set Up Axis to Z Axis, and enable the stream.

3. (optional) click the red point to start log. Click it again to stop. Then you can save the log file. We use ENU frame of data in log config:

After motive sends the data to the LAN, download this code on the computer that needs to get the data and compile and run vrpn_client_node.

Build

Build the code:

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src
git clone https://github.com/SCUT-DuctedFan/vrpn_client_ros.git
cd ..
catkin_make

another way for use vrpn-client-ros

1. sudo apt-get install ros-noetic-vrpn-client-ros
2. ping server ip
3. roslaunch vrpn_client_ros sample.launch server:=192.168.3.252

For visual directly

1. cd ~/catkin_ws/src catkin_create_pkg optitrack

2. cd ~/catkin_ws/src/optitrack mkdir launch

Add lunch like this repos.

3. cd ~/catkin_ws/src/optitrack mkdir config

Add config like this repos.

4. cd ~/catkin_ws catkin_make

5. Source devel/setup.bash

6. roslaunch optitrack sample.launch server:=192.168.3.252

for raspberry pi, don't run rviz.

Run vrpn_client_node

connect to the same wifi with motive computer(IP: 192.168.3.252), and then run

192.168.3.252 is the computer ip which running motive

roslaunch vrpn_client_ros sample.launch server:=192.168.3.252 

Result

we can see rviz, and the frame is ENU.

Run the follow command to print the topic of ros:

rostopic echo /mavros/vision_pose/pose

the terminal output is

---
header: 
  seq: 9390
  stamp: 
    secs: 1682315199
    nsecs: 620635421
  frame_id: "world"
pose: 
  position: 
    x: 1.7827200889587402
    y: -1.8732807636260986
    z: 0.8786203861236572
  orientation: 
    x: -0.0005116735119372606
    y: -0.0013188595185056329
    z: -0.05677390471100807
    w: 0.998386025428772
---

Run mavros

finally, install mavros and run it by follow command, then the data transfer to pixhawk. install mavros from Binary is simple:

sudo apt-get install ros-${ROS_DISTRO}-mavros ros-${ROS_DISTRO}-mavros-extras ros-${ROS_DISTRO}-mavros-msgs

Then install GeographicLib datasets by running the install_geographiclib_datasets.sh script:

wget https://raw.githubusercontent.com/mavlink/mavros/master/mavros/scripts/install_geographiclib_datasets.sh
sudo bash ./install_geographiclib_datasets.sh

Or you can build it from source.

ROS uses ENU frames by convention. Assume the Optitrack system have set Up Axis to Z Up, and the data obtained by using the vrpn_client_node node is ENU frame. Through topic remapping, mavros/vision_pose/pose is obtained. MAVROS is responsible for converting the ENU frame of mavros/vision_pose/pose into the NED frame used by px4.

fcu_url is the usb dev, gcs_url is the QGC(ground control station, gcs) computer IP.

roslaunch mavros px4.launch fcu_url:=/dev/ttyUSB0:921600 gcs_url:=udp://@192.168.3.190

or after setup by USB Serial Port Software setup on Linux, run

roslaunch mavros px4.launch fcu_url:=/dev/ttyPixhawk:921600 gcs_url:=udp://@192.168.3.190