Pointing PR2 head at something in the camera frame
I'm running a face detector, and would like to be able to point the head at a detected face. As it stands now, I get the face pixel coordinates, use the camera geometry to project that point to a 3D ray, and add a frame with that ray as a child of the optical frame of the camera I'm using. This all works fine - the problem comes when I point the head at that new frame. Since it's a child of the optical frame, when the head moves, the face frame moves along with it making it so once the move head action is done, the face frame is in a different location, so the head moves again.
I've tried adding the face frame as a child of some frame that doesn't move with the head (base_link), but am having trouble getting this to work right since to lookup that transform, I have to broadcast the face frame first, then lookup base_link -> face not knowing if the head is currently moving.
This seems like a common task that should have a standard solution. What's the right way to point the head at something detected in a camera image?
