Obtain co-ordinates from optical flow lines?

Hi, I'm busy trying to develop a reliable people counting program. I am trying to detect people using Lucas-Kanade optical flow and the vision.opticalflow object, I'm using a lot of similar code to the simulink example; 'viptrafficof' but am trying to implement it in code, with a GUI.

I am successful in obtaining optical flow lines:

".. im = step(converter, frame); of = step(opticalFlow, im); lines = videooptflowlines(of, 20); "

What I want to know is how to get the co-ordinates of the points in the 2nd frame (ie. the 'tracked points) from these lines?

Thanks!