3D tracking with green screens is always a bit problematic since the depth information of the scene is almost entirely lacking, which is why you really need tracking markers placed at varying depths from the camera for the best results. If the tracking marks are only on the green screen backing itself there is almost no parallax to speak of.
You’ve already noticed that you can get a track off things like your trashcan which are not on the same plane as the backing. It’s pretty easy to set up depth markers, and typically ping pong balls mounted on sticks work well.
You might also ask yourself if you really need 3D tracking for your project and whether you can make do with (Mocha) planar tracking, which would make life a lot easier.
Simon Ubsdell
tokyo productions
hawaiki