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Two Arms Holding a Package
If two arms are holding the same thing, it's no longer a true hierarchy... there's a loop. That can't be handled directly in the GeoH system at present (it would be a bit complex, not very fast, and likely not used very often). Instead we'll propose a way to work around it (for this example and other loops).
GeoH track one arm, and the package, typically the most visible and robust one.
Add a supervised tracker to some feature visible on the package mesh, ie all the way at the end of the loop. This is always possible: in extreme examples you can put a small mesh sphere at some location on the end
effector, hide the background image and all other meshes, then render a new Preview Movie containing only the small sphere.
Use the "Animate Trackers from Mesh Projection" script to convert the tracker to a mocap tracker on the surface of the mesh. (Note that a better script could create a mocap tracker for this directly from a location on the mesh, if we had such a script.)
Set up to GeoH track the second arm, putting the mocap tracker on the final hand GeoH object. You'll need to set up some tracking for the rest of the arm too. The hand will need to Affect Parent, probably for some or all additional levels.
Run the tracking for the second arm.
Because of the final mocap tracker constraint, the solve will be forced to make the hand show up at exactly the right location to match up with the tracked package, just as if they had been tracked together as a loop.
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