Why is the rubbersheeting tacked on as the second step of a true rotation or general perspective transformation rather than offered as a transformation of its own?
By using the true rotation or general perspective transformation is a preliminary step, the rubbersheeting adjustment can be extended to the four corners of the image. If this was not done, the rubbersheeting would be limited to the convex net of the registration points (that is, limited to the area defined by an elastic band around the registration points).
