Motion Capture Overview

Here’s a quick overview of several types of motion capture.

Inertial

Manufacturers:
– Animazoo
– XSens/Moven

These use an inertial sensor on each limb for measurement, as well as a software model of the biomechanics of the human body to help compensate for the innate drift that inertial systems experience.

Benefits:
– Wide area tracking (can combine with an Intersense IS1200 to lock the character into the same tracking position as the Previzion camera tracking data). Can track over a whole soundstage.
– Can operate under costumes; does not need to be visible

Problems:
– Inertial tracking not as accurate as optical based methods
– No provision for face or finger tracking
– Problems can arise when character’s feet are off the ground

Active LED Marker

Manufacturers:
– PhaseSpace

Uses pulsed LED lights blinking at specific frequencies, along with very fast linear array cameras arranged in a circle around the tracking volume

Benefits:
– Most accurate tracking, in millimeter range
– Each LED blinks at a different rate, so the markers can’t get mixed up — less need for data cleanup in post production
– Provisions for face and finger tracking
– Very, very fast tracking — up to 400 Hz

Problems:
– Expensive to scale to large tracking ranges (needs many cameras)
– Markers on subject need to be wired up and visible

Passive Marker Optical

Manufacturers:
– Vicon
– Motion Analysis
– NaturalPoint

Uses passive retro-reflective “ping pong balls” on subject, with optical cameras arranged in a circle around the tracking volume.

Benefits:
– More accurate than inertial tracking, less accurate than active marker LED
– Provisions for face and finger tracking
– Low cost entry level systems ($6k for NaturalPoint OptiTrack)

Problems:
– Markers have to be visible on subject
– Cameras can be confused on which marker is which, leading to increased data cleanup in post production
– Expensive to scale to large tracking ranges (need many cameras)