E.G. Schlechtendahl - Böcker

Edited for Working Group 2 (WG 2): Cisigraph, Cranfield Institute of Technology, Danmarks Tekniske Hojskole, Kernforschungszentrum Karlsruhe GmbH, NEH Consulting Engineers ApS, Universitat Karlsruhe

ESPRIT Project 322, "CAD Interfaces", has been established to define the most important interfaces in CAD/CAM systems for data exchange, data base, finite element analysis, experimental analysis, and advanced modeling. The definitions of these interfaces are being elaborated in harmony with international standardization efforts in this field. One principal goal of the project is to develop techniques for the exchange of CAD information between CAD systems, and from the CAD domain to CAA (Computer Aided Analysis) and CAM (Computer Aided Manufacturing). This volume presents a proposal for a neutral file format for CAD data: curves, surfaces, and solids. The specification is based on a reference schema for CAD data bases and is defined informally with respect to its semantics and formally with respect to its syntax. This volume is a revised edition of "Specification of a CAD*I Neutral File for Solids" Version 3.2. The revision reflects the enhancements which result from the implementation of communication processors in eight different CAD systems and from the practical exchange of solid models between these systems. Due to the close interaction between the CAD*I project and the coming-up international standard STEP this specification also serves as an introduction to the geometry model that will be included in the future international standard.

Principal authors: U. Kroszynski, B. Palstr9Sm 1.1 The evolution of concepts and specifications for CAD data exchange The CAD/CAM community has witnessed, during the last decade, the appearance of several specifications as well as proposals for standards which either attempt to cover wider areas or to be more reliable and stable than the others. With the rapid evolution of both hardware and software, the capabilities offered by CAD systems and CAD based application systems are far more advanced than they were only ten years ago, even when they are now based on micro-computers or personal comput­ ers. The situation with standards, however, is not and cannot be so. In order to be reliable and accepted by a wide community of both vendors and users, a standard has to be sta­ ble. This implies a life span of at least a decade. This also implies that the standard has to be general and flexible enough to accommodate present as well as expected future developments. 1.1.1 IGES The initial development of concepts for CAD data exchange is strongly influenced by the US Integrated Computer Aided Manufacturing (ICAM) programme, that dealt with the development of methods for data exchange. In September 1979, a subgroup was estab­ lished with participation of the National Bureau of Standards, the General Electric Com­ pany, and the Boeing Company. The result of this effort was the Initial Graphics Exchange Specification (IGES) that was published as a NBS report [61] in 1980.