Many types of motion capture are possible. Any data source, including a mouse, a dial knob, or a MIDI input, can be used to control animation or any other parameter.
Optical motion sampling systems provide extremely dense data (often more than 200 samples per second) and can sample data in a large space. However, they cannot provide real-time feedback and must operate in an unobstructed environment. Optical systems also only generates positional data.
Optical tracking gear is generally used as input for Alias inverse kinematics to drive a skeleton rather than a filter such as the Biped filter.
Magnetic sensing gear provides rotation and position information required by the Biped filter. The Ascension Flock of Birds and the Polhemus UltraTrack are the recommended magnetic sensing systems.
Both optical and magnetic systems have their ideal applications and the system should be chosen to match the intended use.