Okay I am going to start this question off with asking you to picture in your mind this: Imagine you have a large circular dow rod that is very think, and it is covered in green paper. Now at the top of this dow rod covered in green paper or painted green what ever you prefer, there is a chair positioned so that it sits on top as so it looks balanced. Now the question. If I want to make this chair look like it's floating I can video this chair, then move the chair and dow rod, and film what I call empty space. Then in editing I can put the green screen layer on top, then the empty space on bottom and get the desired effect. Here's the problem though, if I walk around and behind the chair and the dow rod, then in post when I apply the effect I will be lost when I cross behind the green dow rod. So how can I achieve this?