Though the display on the CRT monitor always presents a 2 dimensional picture, it is not necessary that the data stored in the computer about the picture also should be two-dimensional. In particular, when one is taking data from 3-dimensional models it becomes necessary to map input data, which is 3-dimensional in nature into the 2-dimensional pictures. This aspect will be dealt with in a later chapter. However, the input devices should be able to read and transfer data from a 3-dimensional world, in the first place. The devices that we have seen so far, namely the mouse or light pen or joysticks or even tablets work only on two-dimensional data only
The concept is that when two perpendicularly placed microphones can pick up signals and identify them in a 2 dimensional space, 3- perpendiculorly placed microphones can pickup and identifies signals in a 3- dimensional space. The result is the above figure
But when a 2 -dimensional tablet is made 3-dimensional by adding a third, perpendicular microphone, the tablet becomes more difficult to manage because of the bulk. Hence one more mechanism, wherein a 2-dimensional tablet can be used to affect a 3 dimensional recognition was developed.
In this case, all the four sides of the tablet are provided with a microphone each and it can be mathematically shown that any sound made by the stylus tip at a height above the tablet is picket up by the four microphones, the time delays will be proportional not only to the x and y distances of the stylus form the microphones, but also to it’s height above the stylus – the z distance. By using very simple mathematics – it is possible to separate the x,y and z values, i.e. the actual position of the stylus
One more simple method of tracking in 3 dimensions is by the use of wires in 3 dimensions. The trick is to connect the stylus to 3-wires, positioned in x,y and z direction, connected to several length of wires and which are spring loaded. The distance of the stylus from each of these springs is proportional to the force applied on the springs, which can be used to indicate the position. However, this method is less accurate and is seldom used