Virtual reality (VR) technology emerged in the 1980s, with the development and marketing of systems consisting of a head mounted display (HMD) and datasuit or dataglove attached to a computer. These technologies simulated three-dimensional (3-D) environments displayed in surround stereoscopic vision on the head-mounted display. The user could navigate and interact with simulated environments through the datasuit and dataglove, items that tracked the positions and motions of body parts and allowed the computer to modify its output depending on the recorded positions. Other types of VR that arose subsequently included projection virtual reality, in which users who wear special glasses interact with three-dimensional virtual models that are projected in a room and can be perceived from different angles, and desktop virtual reality, in which users stereoscopically view a virtual environment represented on a computer screen (using special stereo glasses) and interact with it using datagloves, or...