Optical Touch Screen and Its Application as a Next Generation Classroom Response System - Virtual Reality and Environments - page 121

P sin   P cos   d

 

x 2 y 2 2 y

2

 . (6)

P cos   P sin   d N

x 2 y 2 2 x 2

By solving Equations 1 and 2 we can get the original position of [P x , P y ] T as

CB  CB



12 21

P 



x

AB  AB



12 21

(7)

AC  AC

 


12 21

P

y

AB  AB

 12 21

where

AN  sin   cos , AN  sin   cos ,

1 1 1 1 1 2 2 2 2 2

BN  cos   sin , BN  cos   sin ,

1 1 1 1 1 2 2 2 2 2

C  0, C    d  N d .

1 2 22 x 22 y

The corresponding cursor position of the pointer is obtained as P s =[P sx , P sy ] T =[(P x -s 1x )/s px ,
(P y -s 1y )/s py ] T where s px and s py are pixel sizes of the display unit at both X and Y directions.
Please note that the values of s 1x , s 1y , d 2x , d 2y can be obtained from initial calibration.
However, they will not change even if the display is moved since the cameras and the screen
are both fixed to the same supporting structure.

3. Pointer Locator Using Monovision (PLUM)

3.1 Pseudo-stereovision
In normal stereovision, the surroundings of the interested features is often full of image noises.
However, the scenes observed by the point-detecting cameras are simple and constructed.
Therefore, we can use one camera instead of two to achieve the same result.

Fig. 3. One configuration of Pointer Locator Using Pseudo-Stereovision.