Is it possible to use four corners of a single marker for a plane track?

Question

When tracking smooth and round objects, it can be quite difficult or even impossible to place markers to any specific features. On the other hand, it is often quite easy to track the object as a whole with one marker set to Affine or Perspective motion.

Unfortunately, even if such a large marker succeeds to perfectly track the whole object, it cannot be used to create a Plane Track. Plane tracking always needs four markers. Is there a way how to get around this limitation?

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Edit: The inspiration here was a videoclip where people have sunglasses filled with funky textures:

Placing several trackers on each of the sunglasses, perhaps on their edges, would be quite unreliable. However, it is easy to track glasses with a single marker like this (movie screenshot):

I am looking for a way how to use the precise orientation of an object tracked this way.

Answer 1

Using Python, we can just create a new track for each of the corners, which in turn allows to create a classical Plane Track.

  tracking = D.movieclips['clip.avi'].tracking
  begin, end = C.scene.frame_start, C.scene.frame_end
  corners = [tracking.tracks.new(frame=begin) for i in range(4)]
  track = tracking.tracks['Track']
  for frame in range(begin, end+1):
     track_marker = track.markers.find_frame(frame)
     for i, corner in enumerate(corners):
        corner.markers.insert_frame(frame)
        corner_marker = corner.markers.find_frame(frame)
        corner_marker.co = track_marker.pattern_corners[i]
        corner_marker.co += track_marker.co

However, this is quite clumsy a solution.

Answer 2

You can try to track the entire head along with the sunglasses. You can then position a plane relative to the head and set the plane up to move with the head.