1. A system for generating electrical signals representative of the position of a three-dimensional body relative to a supporting surface, comprising: means for creating an optical image of the silhouette of said body in a first direction; means for receiving the optical image and for generating electrical signals representative of the outline of the body; means for receiving said electrical signals representative of the outline of the body and for generating electrical signals representative of the location of the centroid of the area of the object as viewed from said direction relative to the supporting surface; and means for receiving said electrical signals representative of the outline of the body as viewed from said direction and for generating a signature signal said signature signal being representative of the positions relative to one another of a plurality of positions on the outline of the body, all of said positions having equal displacement from the controid of the body.