For the effective use of computer technology in support of design and manufacturing one would need to access large active databases for the efficient manipulation of information. In this context, it is envisioned that 3-D object models can be easily retrieved for modification, or for simply reviewing related information. This thesis addresses the development of a classification system for the efficient retrieval of CAD models of 3-D objects. For the de- sign of a new object the user would access the database to locate the most similar object model, and if worthwhile, mocify it to attain a model for the new object under consideration.

The classification procedure developed in this thesis comprises three main stages:​ First, 3-D geometrical data, sufficient for classification, is determined and extracted from a selected model of the 3-D object, and a primary rep- resentation domain is determined. Contours, solid and hollow, were selected as the basic descriptive units. Based on this selection, relationships defined by descriptor elements were established between (a) two solid contours;​ (b) a solid and a hollow contour;​ and, (c) two hollow contours. In order to fa- cilitate the use of the descriptor elements, a simple alpha-numeric coding system was developed.

Second, the description of a 3-D object is mapped from the geometrical domain into a numerical-factors domain, where each contour is represented as a point. A set of representative factors was developed for this purpose.

The final stage depends on the complexity of the 3-D object at hand. For the case of 3-D objects with cavities or protrusions, which have a localized effect on the shape of the object. a similarity measure based on the factor-domain representation is obtained and used for classifying the CAD object models. For 3-D objects with more complex features, a code is generated from the factor-domain representation in the form of a Fourier signature. Classification is then carried out according to the similarity of the generated Fourier signatures.