Hasta La Motion!

I have a static scene with a camera solved (done by eye, had a similar one with a simple tilt too, just to get me a camera to work with)

into the frame drops an object that bouncing to a halt mid air with a subtle bounce and movement at the end.

I need to stick something to this object, and have been object tracking it so far with crude geometry (hence the basic camera)

I had a grand idea to make a 2d track of the objectdropping into frame, and then turning that screen coordinate into a 3d point using the camera, hence getting me a travelling axis that all I had to do was rotate by eye.

but that’s the wall I hit, as I can’t get my head around how to convert the data to 3d, a kind of Reconcile2d, but the other way round, so a Reconcile3d so to speak.

am I chasing a red herring here, or missing something blindingly obvious?

cheers for any help

mike.c