Make a hole in the ground of a video which is camera-tracked? With my trial and error learning, I managed to track a video in Blender 2.67 and make a cube (the one which is there by default) appear on the "ground" (which is a table).

But how can I make a hole in the ground?



Edit:

I used the two buttons shown below:



The two functions seems to do a bunch of things to the scene, which seems to include setting the background and foreground layers, and adding a Ground object to the scene.

The problem is, what do I need to do to create a hole that appears to sink into the table?
Firstly, you need to create the shape of the inside of the hole and make sure the object is on the foreground layer.

After that, you need to crop the generated Ground object to remove an area which matches the opening of the hole.

Here is the result (not realistic, just to show that it works):



This is the way I did it. I guess this might not be the best way to do it, but it works.

I am not familiar with Blender terminology. If someone is willing to post a more detailed or better answer, I would be glad to accept it.