During the late 1970s, engineers and information scientists saw the need to communicate designs, in the form of engineering drawings, among the variety of computer-aided drafting (CAD) systems coming into widespread use within the engineering community. Personnel from Boeing and General Electric collaborated on a scheme to make it possible for different CAD systems to exchange data without resorting to special programs to translate from one internal database to all the other possible formats. KELLY[1] The scheme was conceptually simple: define a file format that all systems could understand (i.e., read and write). Then when two different CAD systems needed to exchange data, the sender would produce the neutral data file for the receiver to read. Out of this early work evolved the Initial Graphics Exchange Specification (IGES), which was developed by an all-volunteer organization including representatives from industry, government, and academia. NAGEL[2] The first specification was completed in 1980 and became an American National Standards Institute (ANSI) standard in 1981. Y14.26M[3] The original specification dealt mainly with the representation of two-dimensional engineering drawings, but did include some capability to exchange three-dimensional curves and surfaces. As CAD systems evolved from purely drafting applications to computer-aided drafting and design (CADD) functions, then to today's computer-aided design (CAD) workstations with solid modeling capabilities, the IGES community recognized the need for a mechanism to exchange solid models as well as flat drawings. The IGES 4.0 specification, completed in June of 1988, includes capabilities to represent constructive solid geometry models. SMITH[4] This version of IGES became an ANSI standard (ASME Y14.26M-1989) in 1989 and is entitled Digital Representation for Communication of Product Definition Data. ASME[5] ASME Y14.26M-1989 is the current standard and is the basis for the work presented in this report. But the latest version of IGES (Version 5.1) was released in September of 1991 and will soon begin the process toward becoming an ANSI standard. The major enhancement in IGES 5.1 is additional capability in the solid modeling area namely, support for boundary representation models. REED[6] When this IGES version becomes a standard, the capabilities will exist for virtually complete exchange of solid models among unlike CAD systems.

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