Jmo34 at 20:12, 24 June 2008

2008-06-24T20:12:56Z

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[[Image:iges.svg|right|150px]]
The '''Initial Graphics Exchange Specification (IGES)''' (pronounced ''eye-jess'') defines a neutral data format that allows the [[CAD data exchange|digital exchange]] of information among [[Computer-aided design]] (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'''. Many documents (like the [[Defense Standard]]s [[MIL-D-28000]] and [[MIL-STD-1840]]) refer to it as '''[[American Society of Mechanical Engineers|ASME]] Y14.26M''', the designation of the [[ANSI]] committee that approved IGES Version 1.0.

Using IGES, a CAD user can exchange product data models in the form of [[circuit diagram]]s, [[wire frame model|wireframe]], [[freeform surface modelling|freeform surface]] or [[solid modeling]] [[Representation (arts)|representations]]. Applications supported by IGES include traditional [[engineering drawing]]s, models for analysis, and other [[manufacturing]] functions.

==History==
[[Image:gehaeuse.gif|thumb|right|240px|Test IGES file used to demonstrate vendor interoperability at AUTOFACT-6 in [[Anaheim, CA]] in 1983]]
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 [[U.S. 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.

Since [[1988]], the DoD has required that all [[digital]] [[Product Manufacturing Information]] (PMI) for weapons systems contracts (the engineering drawings, circuit diagrams, ''etc''.) be delivered in [[computer file|electronic]] form, specifically in IGES format. As a consequence, any [[CAx]] software vendor who wants to market their product to DoD subcontractors and their partners must support the import (reading) and export (writing) of IGES format files.

An ANSI standard since [[1980]], IGES has generated warehouses full of magnetic tapes and CD-ROMs of digital PMI for the [[automotive industry|automotive]], [[aerospace]], and [[shipbuilding]] industries, as well as for weapons systems from [[Trident 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 this data decades from now. Today, plugin viewers for [[Web browser]]s allow IGES files created 20 years ago to be viewed from anywhere in the world.

After the initial release of [[STEP (ISO 10303)|STEP]] in [[1994]], interest in further development of IGES declined, and Version 5.3 ([[1996]]) was the last published standard. A decade later, STEP has yet to fulfill its promise of replacing IGES, which remains the most widely used standard for [[CAx]] and PMI [[interoperability#Software|interoperability]].

==File format==
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 computer]]s 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 misread.

Here is [http://www.iges5x.org/misc/igs/slot.igs a very small IGES file] from 1987, containing only two POINT, two CIRCULAR ARC, and two LINE entities. It represents a slot, with the points at the centers of the two half-circles that form the ends of the slot, and the two lines that form the sides.

<pre>
S 1
1H,,1H;,4HSLOT,37H$1$DUA2:[IGESLIB.BDRAFT.B2I]SLOT.IGS;, G 1
17HBravo3 BravoDRAFT,31HBravo3->IGES V3.002 (02-Oct-87),32,38,6,38,15, G 2
4HSLOT,1.,1,4HINCH,8,0.08,13H871006.192927,1.E-06,6., G 3
31HD. A. Harrod, Tel. 313/995-6333,24HAPPLICON - Ann Arbor, MI,4,0; G 4
116 1 0 1 0 0 0 0 1D 1
116 1 5 1 0 0D 2
116 2 0 1 0 0 0 0 1D 3
116 1 5 1 0 0D 4
100 3 0 1 0 0 0 0 1D 5
100 1 2 1 0 0D 6
100 4 0 1 0 0 0 0 1D 7
100 1 2 1 0 0D 8
110 5 0 1 0 0 0 0 1D 9
110 1 3 1 0 0D 10
110 6 0 1 0 0 0 0 1D 11
110 1 3 1 0 0D 12
116,0.,0.,0.,0,0,0; 1P 1
116,5.,0.,0.,0,0,0; 3P 2
100,0.,0.,0.,0.,1.,0.,-1.,0,0; 5P 3
100,0.,5.,0.,5.,-1.,5.,1.,0,0; 7P 4
110,0.,-1.,0.,5.,-1.,0.,0,0; 9P 5
110,0.,1.,0.,5.,1.,0.,0,0; 11P 6
S 1G 4D 12P 6 T 1
</pre>
The file is divided into 5 Sections, indicated by a character (S, G, D, P, or T) in column 73. The characteristics and geometric information for an entity is split between two sections; one in a two record, fixed-length format (the Directory Entry, or DE Section), the other in a multiple record, comma delimited format (the Parameter Data, or PD Section). Here is a more [http://www.iges5x.org/misc/peek/slot.txt human-readable representation] of the file.

When displayed, the user should see two [[yellow]] points (hard to see on a [[white]] background, but most CAD systems use a [[black]] background), one located at the [[origin]] of model space [0,0,0], two [[red]] circular arcs, and two [[green]] lines.

[[image:slot.gif|center]]

==A Recursive Standard==
One of the unique features of the IGES standard is that it was the first [[ANSI]] Standard to be documented using itself. Since Version 4.0, all of the technical illustrations for the printed version of the standard have been generated from IGES files. The electronic publishing system ([[LaTeX]]) integrates raster images generated from IGES files into the [[PostScript]] sent to the [[laser jet]] [[computer printer]], so text and images are printed on the same page for subsequent use as camera-ready copy for commercial publication. Beginning with IGES Version 5.2, this is how the standard was generated, and Version 5.3 (the most recent ANSI approved version) is available as a [[PDF]] document.

Many of the illustrations (all of which conform to the Defense Department's MIL-D-28000 Engineering Drawings Subset of IGES) use the entities that they describe, ''e.g.'', the illustration of the LEADER (ARROW) ENTITY (Type 214) can be used as a test case for translator implementers, because it contains all 12 arrow head styles defined by the standard. These [[WYSIWYG]] example files can be distinguished by a leading "F" and trailing "X" in the file name (like "[http://www.iges5x.org/wysiwyg/f214x.shtml f214x.igs]"), and this library is called the '''IGES [[X-files]]''' by members of the IGES [[community]].

Here is one of the example figures, Figure 2 from Appendix A ([http://www.iges5x.org/misc/figa2.shtml  fmeparte.igs]), that has appeared in every version of IGES since Version 3.0. It uses linear, angular, and ordinate dimension entities, as well as examples of both [[Conic section|circular and conic arcs]]. It is usually the first part used when testing an IGES translator, because the standard has a picture of what it should look like.

[[Image:figa2.gif|center]]

==External links==

* [http://www.uspro.org/documents/IGES5-3_forDownload.pdf IGES 5.3 (ANSI-1996)] in PDF from US Product Data Association (USPRO)
* [http://www.iges5x.org/ IGES 5.x Preservation Society] has sample IGES files for testing translators
* [http://www.dt.navy.mil/tot-shi-sys/des-int-pro/tec-inf-sys/cal-std/doc/1840c.pdf MIL-STD-1840C] from ''navy.mil''
* [http://www.acq.osd.mil/log/lpp/spec_standards/mil-prf-28000b.pdf MIL-PRF-28000B] from ''osd.mil''

IGES - Revision history

Jmo34 at 20:12, 24 June 2008