For objects in 2D plane, it is pretty simple to calculate the displacement vectors using optical flow algorithms such as SLIC, LK, Färneback etc.
But how it is possible to know the magnitude of the flow of objects when the motin is rigid i.e the object size increases ( coming towards you ) or the object size decreases ( going away from you ).
I guess the original size of the object is immaterial because we are looking at frame to frame displacement. Is this statement correct?
Are there current algorithms that returns the flow of rigid motions?