How to define an anterior position?

Hi,

In my program, I have a ball moving from point A to point B, her position defined by x and y coordinates. I am trying to find a way to define her anterior position, to be able to check if she hits an object in her path (I can trace a line with the coordinates of the point A to B to look if an object touch this line).

Sorry for my english, but I'm in need with this problem, thanks in advance!

[Image Analyst]

So you have female balls, huh? Okay - first time I've heard of that. But what do you have to work with? Is it a female ball robot with cameras and on-board MATLAB which can process an image and tell the robot ball which way to turn to avoid obstacles? Or is this strictly a software simulation? Like you're plotting a path on a grid with obstacles positions at predefined places (grid locations)?