Product Data Exchange; Design and Implementation of IGES Processors

Abstract

The Initial Graphics Exchange Specification (IGES) was introduced in 1981 as an american (ANSI) standard for the exchange of product data between dissimilar CAD/CAM systems. Since then, vendors and users of CAD/CAM systems have designed and implemented IGES translators. When these translators were actually used in translation processes many problems surfaced. These problems were created by both the IGES standard itself and the translators. This paper describes both, (1) the attempts of various national and international standards groups (such as NBS in the USA or DIN in Germany) to improve the existing standard and define an ISO standard and (2) a design concept for IGES translators that solves many of the implementation problems.

The creation of one international product data exchange standard is the common goal of the various national standard groups in the International Standards Organization (ISO). Because of the well known deficiencies of the current IGES standard a twofold approach seems to emerge. One, to correct the existing IGES to make it practically applicable and the other to define a new standard that goes far beyond the scope of the existing IGES. The state of these activities is described and the different national positions are explained.

The design described in this paper is based on IGES 2.0. It allows for the successful exchange of subsets of product data even with the deficiencies of the existing IGES. Central to the design is the restructuring of the original IGES file into the Internal IGES Files (IIF). Instead of IIF record descriptions, a subroutine package (the IIF Interface) provides access to IIF. The design divides the IGES translation into two phases, the conversion between IGES and IIF (Edit phase), and the entity translation between IIF and the target CAD/CAM system (Exchange phase). This design allows implementation of IGES translators for different CAD/CAM systems with a reduced programming effort. Allowing endusers to control entity mappings in the Exchange phase, the design adds flexibility to the translation process.