Planes, Faces, Problems

[o m n i]

Hey I have problem here, more math related than directly code related. I have a bunch of planes that define a shape, but I need to get the actual faces of the shape (ie. have points where they connect and end rather then extending on forever). I haven't found any math libraries that have functions to do this so I was wondering if I could get some help here. I think I need to find, for each face, where it intersects with other faces, and somehow position a point there, but I'm not really sure, not very good with 3d math.