A tutorial on Motive / OptiTrack

In robotics, motion capture can be used for creating accurate localization within a defined space. This can be used for evaluating the responses of systems or for ease of development and real-world testing of path planning algorithms among many other things.

A recent popular example of those that have used motion capture for robotics can be seen in StuffMadeHere's video on his latest iteration of the robotic basketball goal.

Recently, at my University a motion capture system was installed in one of the labs and I was shown how to use it. The system is made up of several cameras installed into the ceiling of a regular classroom connected to a Windows computer. Specifically, the system is made up of several OptiTrack Flex 3 cameras.

The system has an available ROS/ROS2 driver that can be seen here:
https://github.com/ros-drivers/mocap_optitrack

TLDR: mocap is cool

Quick-Start Guide:

1. Make sure that the power strips along the wall next to the lab computer are turned on.

2. On the lab computer after logging into your student account, launch Motive:

Something like this should appear:

2. Place the silver reflector balls on the body that you want to track. The reflectors should be visible as orange points within Motive.

3. Left-click drag to select the placed reflectors. Once selected, right click and create a rigid body.

Creating a rigid body:

4. Once the rigid body is created, in order to access the pose / position of the rigid body with the ROS driver, network streaming needs to be turned on within Motive. To do this, there should be an icon like the following available in the top toolbar: 

5. Once the streaming pane has been opened, be sure that broadcasting is turned on and a local network interface is selected. Within this pane, the ports and multi-cast address required for the ROS driver are hidden within the advanced section of the streaming pane.

6. Within the advanced section, the following should be shown:

These ports and addresses align with the configs required for the ROS driver that can be seen here:

7. Be sure that you are connected to the same network as the lab computer, either by connecting to the wifi network of the router on the opposite wall or by connecting to one of the ethernet ports on that same wall. Only some of the ethernet ports work 

Notes:

- The ROS 2 driver, while only being released for ROS 2 foxy, can be built from source and has been tested with ROS 2 Humble.

- If there is a lot of other lighting in the area or if a reflector can only be seen by a couple of the cameras the location of the reflector may seem to noisy.

- Further documentation for Motive can be seen here: https://docs.optitrack.com/