Optical Motion Capture Systems
		Motion Capture  ·  What is it?  ·  Why use it?  ·  Recording vs. real-time  ·  Magnetic ·  Optical ·  Electro-mechanical  ·  Workflow  ·  Specialized tools ·  Who uses it?	Products  ·  Motion Captor  ·  Gypsy  ·  Datagloves  ·  Cybergloves  ·  Face Trackers  ·  MotionBuilder

There are two main technologies used in optical motion capture: Reflective and Pulsed-LED (light emitting diodes).

Optical motion capture systems tend to utilize propietary video cameras to track the motion of reflective markers (or pulsed LED's) attached to joints of the actor's body. Single or dual camera systems are suitable for facial capture, while 3 to 16 (or more) camera systems are necessary for full-body capture. Reflective optical motion capture systems use Infra-red (IR) LED's mounted around the camera lens, along with IR pass filters placed over the camera lens. Optical motion capture systems based on Pulsed-LED's measure the Infra-red light emitted by the LED's rather than light reflected from markers.

The Motion Captor system is a reflective system. It uses widely available off-the-shelf hardware, resulting in very low cost and easy upgrading of system capabilities.

The centers of the marker images are matched from the various camera views using triangulation to compute their frame-to-frame positions in 3D space. Several problems often occur during the tracking process, including swapping of markers, noisy or missing data and false reflections.

Most systems use a skeleton after the marker positions are captured. The Motion Captor system software uses a biomechanical skeleton during capture, allowing it to provide cleaner data with lower likelihood of noise, missing data or false reflections. The captured skeleton moves around the character's skeleton, which moves the mesh that makes up the skin of the character. This results in animation of the character.

continued next page