View frustum / infinite plane intersection?

[CodeMonkey9357]

Could anyone answer this appallingly simple question for me?

I have a camera (with your standard truncated pyramidal view frustum) at almost any point in space, looking at any point on an infinite plane (parallel to x-z, at y=0). How can I calculate the trapezium where the frustum intersects the plane (assuming that the camera is never edge-on to the plane)? Is it possible to retrieve all the information necessary from the View and ViewPlatform objects? Is it really, really simple? Should I already know how to do this?