Geometric data transfer between CAD systems: solid models

The CAD/CAM community is showing great interest in the development of data exchange standards. This article highlights some aspects of the work accomplished during the first phase of the ESPRIT project CAD*1. Part of this work has resulted in a specification for the exchange of solid models, as well as in some pilot implementations of processors based on this specification. This work also contributes to the efforts of the International Standards Organization (ISO) in developing the Standard for the Exchange of Product Model Data (STEP). The authors present a summary of the CAD*1 approach, addressing the structure of neutral files for solids, entities, and attributes supporting three kinds of representations, facilities for the transfer of parametric designs, referencing library components, and other general mechanisms. Also is described the current state of the specification and processor implementations. An example of a CAD*1 neutral file is included. Results from cycle and intersystem solid model transfer tests are presented, showing the practicality of the CAD*1 proposal. B-rep model transfer results are discussed in some detail. Finally, the authors outline the relationship of this work with standardizatio