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OK, enough of stereo vision because there is another important feature to be explained: user tracking. Say you are looking at an image, whether it's on paper or canvas or on the computer screen, and then start moving around it. You don't expect the image to change as you move. When you see the picture of a chair, you won't see the back of the chair if you look behind the picture, or only its left side if you look from the left. But of course that's what you expect in reality!! Well, since we want to create a virtual (an imitation of) reality we have to let you see the left side of a chair if you move to the left and the right side if you move to the right. This is done with the help of user tracking.

The Immersadesk is a VR console that creates a sense of being inside the environment displayed on the screen. The user wears active glasses that produce the stereo effect, and a little transmitter, which signals the system as to head position and orientation to display the appropriate image.   There is also a device attached to the user’s hand that similarly reports its position and orientation so that objects in the scene may be picked up and pushed around. That is done with the help of a wand – a VR device analogous to a computer mouse.

In the virtual world you are a foreign object, an observer who doesn't live in that world. To make you a part of it, we have to tell the computer that you are not just a static observer of the virtual world but that you can move around and that we will provide the information of where you are in the world. Knowing where you are, the computer will adjust the scene to your location and will do it continuously as you keep moving around. You move to the left -- it will show you the "left side" of things; move to the right -- the "right side". Thus, what we need to know is your location. There are various devices, which can track where you are in the real world, and the computer program will map that location into the virtual world. All these devices work on the same principle: you wear a sensor (or many sensors - there are systems which can track even the motion of your eyelids as you wink!), which is some kind of a transmitter, ultrasonic or electromagnetic, and somewhere in the room there is an antenna - a receiver of the signal your sensor sends. The receiver translates that signal into space coordinates in three dimensions: x, y, z, yaw, pitch and roll -- and this is the information computer needs to know to show you the image correctly. And what if there are two people looking at the same world? This is a very difficult problem. Most of today's systems can only track one user at a time, so that if there are other people in the room they need to stay as close to the tracked person as possible, or they will see a distorted picture. There are, however, some systems that have the ability to track positions of two people and send the correct image to each of them.