Hasta La Motion!

I’m reasonably new to composting. I’ve 3D’ing for a while; though it’s only recently that I’ve become enthused by the mixing of virtual and live action media.

I’ve done a few textbook tracking shots, bits of planar tracking in Mocha and some work in Boujou, and I’ve just hit a stumbling block. How would I get a 3D object to float above a person’s head as they move around?

The shot that I’ve setup is essentially a nodal pan, the camera remains on the spot as the person moves around the scene. So far I’ve managed to get a reasonable solve in Boujou, at least as far as the overall scene is concerned. The resulting point cloud reflects the scene geometry, so I’m able to get my bearings; though I’m obviously still reduced to animating the virtual object by hand through the scene. I’m helped a great deal by the predicted points; though it’s hardly a "rock solid" approach to pinning the abject to the individual as they move around.

Any offers on the theory of how this shot is done?

Thanks in advance,

Nick