A new approach to machine representation and analysis of three-dimensional objects is presented. The representation, based on the notion of "skeleton" of an object leads to a scheme for comparing two given object views for shape relations. The objects are composed of long, thin, rectangular prisms joined at their ends. The input picture to the program is the digitized line drawing portraying the three-dimensional object. To compare two object views, two characteristic vertices called "cardinal point" and "end-cardinal point," occurring consistently at the bends and open ends of the object are detected. The skeletons are then obtained as a connected path passing through these points. The shape relationships between the objects are then obtained from the matching characteristics of their skeletons. The method explores the possibility of a more detailed and finer analysis leading to detection of features like symmetry, asymmetry and other shape properties of an object.

Computer simulation of one aspect of the human visual perceptual capabilities, viz., the ability to visualize object views that result from known rotations of familiar objects is considered. The objects considered are composed of long, thin, and narrow rectangular prisms connected at their ends. From the digitized binary picture of the line drawing portraying a given three-dimensional object a description is generated in terms of a set of "cardinal points" (which are key points occurring at the bends and open ends of the object) and a set of direction vectors associated with them. The skeleton for the given view is obtained as an ordered sequence of "slope-code" numbers by tracking between the cardinal points. A set of transformations is defined on the sequence and the direction vectors to get the skeleton of the view that results from rotation. From a knowledge of the transformed direction vectors the machine builds up faces around the bends and ends of the skeleton to complete the new view. As far as machine visualization is concerned, it is shown that object rotations of only integer multiples of π/2 need be considered.