ABSTRACT

Throughout the course of the development of CAD, CAPP, and CAM systems, unambiguous representation of a design's geometry and topology remain an essential part of the task. Since the mid-1990's, the technology has matured enough to enable such a representation. While geometry and topology provides a basic description of a design part, direct use of it for creation of the part and other applications, can be cumbersome. Take creation of a simple plane with four straight edges as an example. For a B-rep model to fully define the plane, four points are to be created first to be used as four vertices. They are used to define four edges, which are connected one after another to form a closed loop. Finally, a fat surface is fitted onto the loop to form the plane. When a cube is to be designed, the above process needs to be repeated five more times for the other five faces though some of the vertices and edges may be re-used. In addition, the directions of the solid have to be defined through each face. Clearly, this is not a trivial task. Users would find it helpful if the creation of geometry and topology is hidden behind them and only some meaningful parameters of the solid are provided. In the case of a simple cube, length, width, and depth would be the parameters. Hence, the concept of features (i.e. cube or block in the above example) emerged, as did the associated technologies. The same applies...