Neutral File Interface Requirements

Abstract

Ideally a neutral file interface for CAD data exchange should make it possible to communicate 100% of the data between any two systems without loss of accuracy or information. The effectiveness of this transfer depends not only upon the neutral file specification but also upon the quality of the pre- and post-processors provided. In the context of sculptured surface data fundamental incompatibilities between the forms of surface representation used by different systems mean that no matter how good the neutral file specification and the processors the objective of 100% interchange between all systems will never be attainable. The practical limit to the amount of data which can be fully exchanged is the intersection of the capabilities of the two systems, the neutral file specification and of the processors concerned. The design of the neutral file is important in that it defines the ultimate scope of the exchange and strongly influences the quality of pre- and post-processors. This chapter will describe some of the important considerations in defining a neutral file and describe how these have influenced the design of the CAD*I neutral file and the ISO draft proposal STEP. The emphasis is on those entities in the neutral file concerned with the communication of parametric curve and surface data.