Light sources on the tracked object have position determined by multiple cameras.

Elements

Markers
Passive	Reflective markers shine when strobes hit
Active	Markers flashing LED lights (in sequence)

Camera Lights
Passive	Illuminates performance area with strobe lights
Active	low or normal lighting

Cameras	2D frames with position of marker from its view
Computer/Software	Interpret the views and positions into 3D space

Vicon MX20+ (2 mega pixel) camera

Pros and Cons of Optical Systems

Pros		Cons
	Accurate and fast (.2mm and up to 10,000 fps)		Ideally needs dedicated space
	Not affected by metal		Not available for portable rental
	No electromagnets		Longer calibration times
	IR		Occlusion problems
	Mature technology		Lines of sight required
	Flexible placement of markers		3dof natively ? positional only, additional triangulated sensors required for 6dof
	Flexibility in using props		Can be expensive (active usually cheaper)
			Markers need to be reapplied each session
			Active units may be bulky