I'm having difficulties with my project. I'm quite new in XNA. Anyway, I'm trying to make 3D game and I'm already stuck on one basic thing. I have terrain made from a heightmap, and an avatar model. I want to set up some collisions for game so the player won't go through the ground. But I just don't know how to detect collisions for so complex an object. I could just make a simple box collision for my avatar, but what about the ground?

I already implemented the JigLibX physics engine in my project and I know that I can make a collision map with heightmap, but I can't find any tutorials or help with this. So how can I set proper collision for complex objects? How can I detect heightmap collisions in JigLibX? Just some links to tutorials would be enough.

Thanks in advance!