Tracking systems are used to relate movement and position in physical space to the CAVELib. CAVELib applications require a user's head position and orientation in order to draw correct images to the defined walls. A second sensor is usually used on the controller (wand) for interaction with the environment, although this is not required. The trackd program supports a number of tracking devices including Ascension Technologies Flock of Birds, Space Pad, pcBirds, Polhemus Fastrack and Ultratrack, and Intersense IS600 and 900. Support for tracking devices is added as products enter the market and become of interest to the community. There is also a trackdSDK available for end-users to create support for their own custom tracking systems. Contact support@vrco.com for more information about adding support for tracking devices.