TheInitial Graphics Exchange Specification (IGES) is a vendor-neutralfile format that allows thedigital exchange of information amongcomputer-aided design (CAD) systems. It is an ASCII-based textual format.[1]: 59
The official title of IGES isDigital Representation for Communication of Product Definition Data, first published in March, 1980 by the U.S.National Bureau of Standards asNBSIR 80-1978.[2] Many documents (like early versions of theDefense Standards MIL-PRF-28000[3] and MIL-STD-1840[4]) referred to it asASME Y14.26M, the designation of theANSI committee that approved IGES Version 1.0.
Using IGES, a CAD user can exchange product data models in the form ofcircuit diagrams,wireframe,freeform surface,boundary (B-rep) orsolid modeling (CSG)representations. Applications supported by IGES include traditionalengineering drawings, models for analysis, and othermanufacturing functions.
IGES was an initiative of theUnited States Air Force (USAF)Integrated Computer Aided Manufacturing (ICAM) project (1976-1984).[5]
ICAM sought to develop procedures (IDEF), processes (Group Technology), and software (CAD/CAM) that would integrate all operations in Aerospace manufacturing and thus greatly reduce costs. Earlier the USAF Manufacturing Technology Program had funded the Automatically Programmed Tools (APT) language for programming Numerically Controlled (NC) machine tools. To close the data gap between parts design and manufacturing, one of the ICAM goals was to develop CAD software that would automatically generate numerical control programs for the very complex Computer Numerically Controlled (CNC) machine tools used throughout theAerospace industry. A serious issue was the incompatibility of data produced by the manyCAD systems in use at the time. USAF/ICAM called a meeting at theNational Bureau of Standards (now known asNational Institute of Standards and Technology orNIST) in 1978 to address this issue.Boeing offered to sell its CAD translation software to USAF for one United States dollar.USAF accepted this offer and contracted NIST to bring together a group of users and vendors, including Boeing,General Electric,Xerox,Computervision,Applicon and others to further develop and test this software. Though it was the practice to begin the name of ICAM developments with the word integrated (for example the IDEFs) believing that there would be rapid development of graphical exchange software, USAF decided that the IGES would be the Initial Graphics Exchange Specification not the Integrated Graphics Exchange Specification.
Since 1988, theDoD has required that alldigitalproduct and manufacturing information (PMI) for weapons systems contracts (the engineering drawings, circuit diagrams,etc.) be delivered inelectronic form such as IGES format. As a result,CAx software vendors who want to market their products to DoD subcontractors and their partners needed to support the import (reading) and export (writing) of IGES format files.
An ANSI standard since 1980, IGES has been used in theautomotive,aerospace, andshipbuilding industries. It has been used for weapons systems fromTrident missileguidance systems to entireaircraft 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 forWeb browsers allow IGES files created 20 years ago to be viewed from anywhere in the world.[6]
After the initial release ofSTEP (ISO 10303) in 1994, interest in further development of IGES declined, and Version 5.3 (1996) was the last published standard.
An IGES file is composed of 80-characterASCII records, a record length derived from thepunched 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 theFortran language). Early IGES translators had problems withIBMmainframe computers because the mainframes usedEBCDIC encoding for text, and some EBCDIC-ASCII translators would either substitute the wrong character, or improperly set theparity bit, causing a misread.
Here is a very small IGES file from 1987,[7] containing only two POINT (Type 116), two CIRCULAR ARC (Type 100), and two LINE (Type 110) 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.
S 11H,,1H;,4HSLOT,37H$1$DUA2:[IGESLIB.BDRAFT.B2I]SLOT.IGS;, G 117HBravo3 BravoDRAFT,31HBravo3->IGES V3.002 (02-Oct-87),32,38,6,38,15, G 24HSLOT,1.,1,4HINCH,8,0.08,13H871006.192927,1.E-06,6., G 331HD. 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 12116,0.,0.,0.,0,0,0; 1P 1116,5.,0.,0.,0,0,0; 3P 2100,0.,0.,0.,0.,1.,0.,-1.,0,0; 5P 3100,0.,5.,0.,5.,-1.,5.,1.,0,0; 7P 4110,0.,-1.,0.,5.,-1.,0.,0,0; 9P 5110,0.,1.,0.,5.,1.,0.,0,0; 11P 6S 1G 4D 12P 6 T 1
The file is divided into 5 sections:Start,Global,Directory Entry,Parameter Data, andTerminate indicated by the characters 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), as can be seen in a more human-readable representation of the file.[8]
When displayed, the user should see twoyellow points (hard to see on awhite background, but most CAD systems use ablack background), one located at theorigin of model space [0,0,0], twored circular arcs, and twogreen lines.
Due to its growing international popularity (several countries, including Australia and the UK, adopted IGES as their own National Standards for PMI interoperability), support was added to the TEXT (Type 212) entity to support theISO 8859 (Latin-1) alphabet for European characters.[9]
In the 1990s, IGES added support for theJIS encoding forKanji (漢字) as double-byte characters (JIS-6226), allowing members of theJapan Automobile Manufacturers Association (JAMA) to exchange part models with their American and European partners without loss of the Kanji text.
The current version of IGES does not supportUnicode 16- or 32-bit character encoding, so Arabic and other scripts (like Thai) cannot be represented.[10]
One of the unique features of the IGES standard is that it was the firstANSI 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. Theelectronic publishing system (LaTeX) integratesraster images generated from IGES files into thePostScript sent to thelaser printer, so text and images are printed on the same page for subsequent use ascamera-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 aPDF document.[11]
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. TheseWYSIWYG example files can be distinguished by a leading "F" and trailing "X" in the file name (like f214x.igs[12]), and this library is called theIGES X-files by members of the IGEScommunity.
Here is one of the example figures, Figure 2 from Appendix A (fmeparte.igs[13]), 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 bothcircular 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.
Formerly an ANSI Standard September 23, 1996 – September 2006
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