The Initial Graphics Exchange Specification (IGES)

The Initial Graphics Exchange Specification (IGES) (pronounced eye-jess) defines a neutral data format that allows the digital exchange of information among CAD systems. The official title of IGES is Digital Representation for Communication of Product Definition Data, first published in January, 1980 by the National Bureau of Standards as NBSIR 80-1978. Using IGES, a CAD user can exchange product data models in the form of circuit diagrams, wireframe, freeform surface or solid modelling representations. Applications supported by IGES include traditional engineering drawings, models for analysis and other manufacturing functions.

The IGES project was started in 1979 by a group of CAD users and vendors, including Boeing, General Electric, Xerox, Computervision and Applicon, with the support of the National Bureau of Standards (now known as NIST) and the US Department of Defense (DoD). The name was carefully chosen to avoid any suggestion of a database standard that would compete with the proprietary databases then used by the different CAD vendors.

An ANSI standard since 1980, IGES has generated warehouses full of magnetic tapes and CD-ROMs of digital PMI for the automotive, aerospace and shipbuilding industries, as well as for weapons systems from missile guidance systems to entire aircraft carriers. These part models may have to be used years after the vendor of the original design system has gone out of business. IGES files provide a way to access these data decades from now. Today, plugin viewers for Web browsers allow IGES files created 20 years ago to be viewed from anywhere in the world.

An IGES file is composed of 80-character ASCII records, a record length derived from the punch card era. Text strings are represented in “Hollerith” format, the number of characters in the string, followed by the letter “H”, followed by the text string, e.g., “4HSLOT” (this is the text string format used in early versions of the FORTRAN language). Early IGES translators had problems with IBM mainframe computers because the mainframes used EBCDIC encoding for text, and some EBCDIC-ASCII translators would either substitute the wrong character or improperly set the Parity bit, causing a misreading.