Eye tracking: How to find reference coordinates?

I'm working on Eye tracking. So far have detected the circular part. I want to know how can i calculate the coordinates of an eye ball? what is the command? And what reference point should be taken.

Please note that finding the center of the eye is not important for me. I just want to detect movement. For example.

At time A: Eye ball is looking straight.

At time B: Eye ball is looking upward.

Thankyou.

Answer 1

[Image Analyst]

I would think that you just have some coordinates from your system depending on where the subject is looking - they might be arbitrary digital numbers coming out of your tracking system, say values in the range of 0-65535 or whatever. And the reference point would be defined by your scene. For example if the subject is looking at a video monitor you might define (0,0) as the upper left corner of the monitor and define the other corners based on centimeters, or pixels, or whatever you want. Then you calibrate by having your subject look at those corner locations and basically derive a transformation that maps your eye tracker coordinates into real world coordinates on the monitor.

[Sharmeen]

Thanks for your answer. But i am new at this. I don't understand what u said about calibration and deriving transformation. There are a couple of questions i have. How can i define/set my reference point? I have a binary image how can calculate the coordinates of any point(i can make it reference point) in the this image. Because after getting those coordinates i have to compare in with the next image and if there is any change in the coordinates it will perform the task i.e in my case it will move the wheelchair.

Also i don't want to do this manually with cursor or pointer because in real time it's not practical.

Please help me by giving step by step procedure/program. Thankyou!