An introduction to Optitrack Motion Capture


Motion capture allows us to record things in motion.

  • Creation: 08/05/2020
  • Update: 03/07/2021

Motion capture is a discipline that consists of capturing elements in a 3D space and reconstructing the space virtually from such elements. Optitrack is frequently used in research in order to localize a object precisely without an internal localization mechanism.

Quick aside: How I structured Optitrack series of tutorials

The Optitrack series will be split in 3 orders of difficulty depending on your needs. Beginners who wish to use the setup unsupervised should look into Tutorial 1: Quick start guide. Precision-dependant scenarios (e.g. drone control via its position) will make use of Tutorial 2: Precision capture theory. Finally, the long-term users might be interested in simplifying maintenance and capture processes with Tutorial 3: Streamlining Capture Processes.

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These tutorials are available at the end of this post.

Areas of application

Motion capture is used in military, entertainment, sports, medical applications, and for validation of computer vision and robotics. In filmmaking and video game development, it refers to recording actions of human actors, and using that information to animate digital character models in 2D or 3D computer animation. Animators use animation for more realistic character movement (as in God of War 4). My particular application helps drones localize themselves, by feeding back their posiiton into their positioning algorithms. The position and orientation of each body is streamed from Optitrack into the drone's ROS framework over the local network.

Basics of optical motion capture

Optical motion capture as we know it today uses infrared cameras to detect the position of reflective trackers. This is optical motion capture and it functions very differently from magnetic motion capture (with piezoelectric surfaces). The tracking elements or trackers are small reflective balls. A camera pointed towards the tracker outputs infrared light via its LED illumination ring. The lens at the center of the ring capture any and all IR incoming light.

Interestingly, the technologies involved in motion capture come with their own set of limitations, mainly that trackers may be confused with one another and undetected at times. These complications are discussed in the "Precision Capture" tutorial.

How to use

Optitrack is a company that offers its own motion capture setup. The hardware setup and the software solution are both available as a package purchase. However, using the setup is a multi-step process. Let's start!