Tracking X and Y coordinates of ONE person

Hello! Me and my friend are doing an interactive installation using Max msp and Processing. We have a web cam hanging from the ceiling looking downwards and tracking people inside a room. We want to limit the tracking to one person and track his movement to get X and Y co-ordinates (this person should be the first entering the tracking space, then when he leaves another person is tracked). By his movements, we mean moving forward or backwards, and right and left, we want to get the coordinates separately as we trigger by that the direction of an animated eye in Processing... In a simpler way, When the person go right or left the eye pupil follows him right and left, and if he goes closer to the projection (forward and backward) this should trigger the size of the iris getting big when he is near and small when he is far. We know we should use cv.jit.track and label but for some reason we cant connect them together to get out the desired output.. Anyone has any ideas ?? we would appreciate that so much as we are have to finish this project this week... Best greetings!