Bird-Doggin' the Internet

Engineering Drawing Formats

Several of you who read the recent article on CAD wanted more information on drawing formats. Some of the issues you face are drawing markup and exchange, transmission of drawings, and compatibility among disparate systems. Like most other topics we have covered, there is more to this topic than merely listing some formats and a few Web sites. The crux of the problem is that there are numerous drawing, image and picture formats -- upwards of a couple of hundred -- and numerous variations within each format. The main formats used for engineering drawings according to CAD practitioners are DWG, DXF, STEP, and IGES. Unfortunately, there is at this time no "universal translator" or perfectly compatible third party system I am aware of that solves this problem. (If I have missed something, please e-mail me and I will share it with the rest of our engineering community.)

DWG and DXF files are the most commonly used formats for component specifiers, builders, machinery designers, and OEM draftspeople. These are native AutoCAD formats and have been covered in previous articles. It is worth noting that while DXF is considered by most CAD people to be a "neutral" translation format, there are numerous DXF implementation which vary in terminology, maximum available numbers of layers and in software version compatibility. A good article by Ralph Grabowski on the subtleties of these variations is available for $9. If this appeals to you, go to <http://www.cadence-mag.com> and look for "Drawing Translation" in the January, 1997 issue. More recent content on the Cadence site is free.

IGES (Initial Graphics Exchange Specification) is a drawing specification, also known as ANSI Y14.26M. Its purpose was to provide a neutral medium which allows other drawing platforms to access drawing data. Both wire frame surfaces and solid representations are supported. If you want spec information for the current Version 5.3 (ANSI/US PRO 100-1996), you'll need to pony up $365. Do this at <https://www.uspro.org/>. For a reasonable synopses of the standard just link to "Preview the CD-ROM. The preview has 34 summary pages in Adobe Acrobat's .pdf format which you can read or print out. Included are contents, lists of figures and tables, entity definitions, and a table of symbols and drafting fonts. Bear in mind that IGES is primarily used by government and large OEMs, such as some automakers and defense industry designers. It is preferred over DXF translators to provide uniform product definition data exchanges from AutoCAD to such systems as CATIA, CADAM, CADDS, Unigraphics, I-Deasr, Pro/E, and Intergraph. It is a commonly used road to CALS compliance. CALS, or Continuous Acquisition and Lifetime support, and is a key requirement for those working with government entities. IGES Workshop/Tools at <  http://www.nist.gov/iges/igesTools.html > has information on configuration, commercially available products, public domain file processing tools, and even a link to a free (beta) IGES viewer for the PowerPC Mac (Only NURB and AND surfaces are supported at this time).

STEP (Standard for the Exchange of Product Model data) is also known as ISO 10303. It was designed to allow companies to effectively exchange information with their worldwide partners, customers and suppliers, as well as internally. Unlike other data transfer standards, STEP is promoted as being "computer sensible." It supports design reuse, data retention, and provides access to data across a product's entire life cycle. A good overview of STEP can be found at < http://www.ukcic.org/step/step.htm >, by the United Kingdom CALS Industry Council. The PDES consortium at < http://pdesinc.scra.org/ > also has information on the merits of STEP, as well as participation vehicles for interested parties. Good sets of links to other STEP resources can be found at VinÌcius Kern's STEP links at <http://sfbox.vt.edu:10021/V/vkern/step.html>, and at the STEP Home Page; Ikeda Labs at <http://www.hike.te.chiba-u.ac.jp/ikeda/documentation/STEP.html>. Some experts believe that STEP will evolve as a replacement for IGES as the human mind strives to encompass and organize all design and production activity from concept to after market support. Whether this is achievable, or even desirable, is a continually debated topic. For various implementation examples, go to the HyperSTEP Home Page at < http://www.igd.fhg.de/www/igd-a2/hyperstep/hyperstep-home.htm >.

One more word on 3-D drawing files. While many CAD vendors are developing and promoting their proprietary keys to the 3-D world, there does appear to be one reasonably open system evolving: that is VRML (Virtual Reality Modeling Language). This is a viewing (versus a design creation) language which has been touted on the Internet in recent years, but has suffered the hobbling effect of limited bandwidth and development support which is yet to be solved. If you're curious, you can check out the toys at the VRML Consortium at <http://www.vrml.org/>.

This column is written by Dr. Steve O'Neil of Micro Mo Electronics, Inc. He can be reached on the Internet at steveo @micromo.com.

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Originally published in the November  1998 issue of designfax.
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