Question 1

What are OptiTrack motion capture markers?

Accepted Answer

OptiTrack markers are small retroreflective spheres (or hemispheres) that attach to a subject, suit or rigid body and reflect infrared light back to OptiTrack cameras. The cameras track the position of each marker in 3D space, which the software then uses to reconstruct movement, skeletons or rigid body objects.

Question 2

What's the difference between passive and active markers?

Accepted Answer

Passive markers are coated in retroreflective material and simply bounce IR light back to the cameras. They require no power or wiring. In fact, sports shoes with retroreflective material can affect tracking in a passive optical tracking volume! Active markers contain LEDs that emit their own light and are typically used for higher-precision or long-range tracking.

Question 3

What sizes do OptiTrack markers come in?

Accepted Answer

Common sizes range from 3mm (typically used for facial and finger tracking) to 19mm in diameter, though 9.5mm, 12.5mm and 14mm are among the most widely used for full-body tracking. Smaller markers suit close-range or facial/finger capture; larger markers improve visibility over greater capture volumes. We have sizes for all applications!

Question 4

How do I attach markers to a suit or rigid body?

Accepted Answer

Markers usually screw onto a threaded base or stud, or attach via velcro backing for fabric suits. Rigid bodies often use pre-drilled marker plates or 3D-printed mounts so marker positions stay fixed relative to one another. It's imperative that markers don't move once attached!

Question 5

How do I stop markers falling off during capture?

Accepted Answer

Ensure that your velcro backing and the velcro adhesive are still in good condition. In some cases, you can add an extra layer of security to a marker by the addition of an extra strip (or 2) of velcro around the base.

Question 6

Can I clean and reuse motion capture markers?

Accepted Answer

Yes! Motion capture markers are designed for continuous use, and only need to be replaced if the retroreflective thread is coming off. If markers are dirty they can be wiped off with a slightly damp microfibre cloth, but only if visibly marked.

Motion capture markers for precision optical tracking

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