IGES is the abbreviation for Initial Graphics Exchange Standard. IGES is very widespread in the CAD world. It can describe both 2D and 3D data. Although its graphics capabilities are limited, it has the particular advantage that it can transfer design details very precisely. In addition to the usual graphic primitives such as lines or circles, it can also describe very complex elements such as surfaces, bodies, dimensions, composite elements and representation parameters.

In practice, the problems often lie in the finer points. In most cases, it is possible to define an element in a variety of ways – a fact that can lead to communication problems between programs. The absence of any uniformity in the description and the lack of any vehicle for monitoring the quality of an IGES file can often result in substantial losses or even prevent transmission altogether.

In an endeavor to reduce this risk, efforts are being undertaken to limit the scope of the IGES standard by creating subsets, which are processed on the basis of specific conventions. Two terms in particular are important in this regard: VDAIS and CALS.

The German Motor Industry Federation (VDA) has defined various groups of elements, which need to be interpreted in a very precise manner. Consequently, a program capable of reading and writing IGES in accordance with the VDAIS specification must also specify the relevant group in order to define the file complexity this program can be expected to handle. Conversely, the IGES files generated by this program must be restricted to those elements defined in the specified group.

The CALS specifications are very similar in purpose. Three classes are defined which set out the scope of the interpretation and the form it is to take. The first class relates to Technical Illustration, the second to design drawings and the third to electrical/electronic applications.

These restrictions were introduced in the hope of making the results of IGES transfers more predictable and of improving quality. Arbortext IsoDraw supports groups 1 and 2 of the VDAIS and classes 1 and 2 of the CALS specification. The elements covered by VDAIS agree for the most part with the specification of the American CALS initiative.

Another problem with IGES files is their size. IGES is by far the largest format in terms of file size. Even small parts can easily generate files of several megabytes. This can mean slower network transfers and may result in storage problems for the reading program. Consequently, only those parts actually required should be selected in the writing program in order to minimize the file size. In the majority of cases, it may therefore be expedient, for example, to deactivate all dimensions, drawing frames and texts.

The graphical capabilities are naturally limited with a CAD format. While line thicknesses and line style patterns can be accommodated in an IGES files without any difficulty, the interpretation results of reading programs differ very considerably. Often, attributes of this type are ignored almost completely.