INTRODUCTION
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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