Perceptual grouping of circular arcs under projection

The world (both natural and man-made) is constrained by physical laws to a finite number of basic patterns. Certain three dimensional relationships between features in a scene give rise to two dimensional relationships that are relatively viewpoint invariant and can be distinguished as non-accidental. Thus, those regularities observable in the image arise not by accident, but are projections of real regularities in the scene. The Gestalt movement proposed that the human visual system applied the principles of perceptual organisation to group image features manifesting those regularities. These were used to recover three dimensional structure from two dimensional views, providing cues to models for scene interpretation.