The term Virtual Reality describes the experience of interacting with data from within the computer-generated data set. The computer-generated data set may be completely synthetic or remotely sensed, such as X-ray, MRI, PET, etc. images. Interaction with the data is natural and intuitive and occurs from a first-person perspective. From a system perspective, VR technology can be segmented as shown in Figure 1. The computer-generated environment, or virtual world content, consists of a 3D graphic model, typically implemented as a spatially-organized, object-oriented database; each object in the database represents an object in the virtual world.