is the abbreviation for Computer Graphics Metafile.

Within the CALS Initiative (Continuous Acquisition & Life-Cycle Support), CGM has been defined as a standard format for device-independent 2D files. The purpose of the CGM file is to store all illustrations so that they can be read and interpreted unambiguously by compliant programs.

CGM is used as a standard format in many different industries. Among them are aerospace (ATA, AECMA), automotive (J2008), Defense (CALS), Telecommunications, Petrochemical industry and others. An area of growing importance for the use of CGM files is the Web environment (Internet and Intranets). Here, intelligent graphics in the WebCGM format are used to generate interactive catalogs and manuals.

CGM is defined as a standard in ISO 8632. The first issue appearing in 1987 described CGM version 1 and attracted a number of significant criticisms. One particularly unfortunate aspect was its very small stock of graphic primitives, since no Bézier or spline curves were defined at all. This means that all curves have to be written as polylines, a fact which results in major disadvantages during further processing.

The communication difficulties become even more apparent if one remembers that the Bézier curve constitutes a key element of almost all PostScript-oriented programs running on various platforms (PostScript knows only the Bézier path!). In addition, there is no direct link to PostScript.

Following a small expansion by a number of segments and other details in 1990 (version 2), an extended version of the ISO standard was published in 1992 which now incorporates version 3 of CGM. This version is much better suited for storing high-quality illustrations.

CGM version 3 was extended to include "Application structures" in 1995 and therefore gave rise to CGM version 4. This means that non-graphic information can now also be saved in the CGM file. This combination allows a whole series of possibilities regarding interactive graphics, hot spots, hyperlinking, etc..

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Concerning which graphics format to use for technical graphics, there has been a lot of marketing and numerous claims, but not much objective data or analysis. That has changed now.

CGM Open has published the results of a study of the applicability of WebCGM and SVG for technical graphics. The study, 8 months in the making, strives for an objective analysis and presents specific data, to help sort out the confusion that has been generated by numerous undocumented claims about one or the other format.

The paper was presented at the IDEAlliance XML Europe 2003 conference and exposition (London, 6 May). It is expected to be updated occasionally at the "Further Readings" page of the CGM Open website, incorporating new information about implementations and interoperability.

You can find the current version of the paper at [1]. Alternately, you can find your way to it from the May 2003 News item on the CGM Open home page [2], or see the paper and presentation linked at the top of the "Suggested Readings" page [3].

[1] http://www.cgmopen.org/technical/cgm-svg-20030508.htm
[2] http://www.cgmopen.org/
[3] http://www.cgmopen.org/technical/readings.html