Interactive WhiteBoard

Hello!

My name is Muneer. I was wondering whether this concept of making a smart board would work(shown in image attached). The idea is to use two distance meters to measure distance ‘a’ and distance ‘b’ from the transmitter in the pen to the top corners. Distance c is fixed and known. Using the distances, the x and y distance should be workable from the formulas I guess.

I have a few concerns and require your expert opinion,

a. How can we construct the distance meter (IR? Ultrasonic? Any available schematic...etc)
b. Converting the x and y distances to pixel information
c. Interfacing the board to a computer, possibly giving the input from the smart board directly as a mouse input.

or if you could suggest other practical ways.

Could you please help me with this? Thanks.