a very profitable business of producing graphics workstations. SGI boxes are some of the most common processors found in VR laboratories and high-end systems. SGI boxes range in price from under $10,000 to over $100,000. The simulator market has produced several companies that build special purpose computers designed expressly for real time image generation. These computers often cost several hundreds of thousands of dollars. Manipulation and Control DevicesOne essential element for interaction with a virtual world, is a means of tracking the position of a real world object, such as a head or hand. There are numerous methods for position tracking and control. Ideally a technology should provide three measures for position (X, Y, Z) and three measures of orientation (roll, pitch, yaw). One of the biggest problems for position tracking is latency, or the time required to make the measurements and preprocess them before input to the simulation engine. The simplest control hardware is a conventional mouse, trackball or joystick. While these are two-dimensional devices, creative programming can use them for 6D controls. There are a number of three and six dimensional mice/trackball/joystick devices being introduced to the market at this time. These add some extra buttons and wheels that are used to control not just the XY translation of a cursor, but its Z dimension and rotations in all three directions. The Global Devices 6D Controller is one such 6D joystick. It looks like a racket ball mounted on a short stick. You can pull and twist the ball in addition to the left/right & forward/back of a normal joystick. Other 3D and 6D mice, joystick and force balls are available from Logitech, Mouse System Corp. among others. One common VR device is the instrumented glove. A basic patent in the USA covers the use of a glove to manipulate objects in a computer. Such a glove is outfitted with sensors on the fingers as well as an overall position/orie...
