IGES file - What is it?

The IGES file (extension .igs, more rarely also .iges) is an ASCII-based file in which construction plans for 2D or 3D objects defined according to the IGES standard are stored. IGES stands for Initial Graphics Exchange Specification. As a manufacturer-independent, neutral file format, IGES can be read and written by almost all common CAD programs and is thus suitable for the exchange of vector-based construction plans. However, since the format has not been further developed since 1996, it makes sense nowadays to fall back on newer file formats. STEP is one of the file formats that can be used here.

History of the IGS format

The history of the IGES specifications goes back to the late 1970s. It was originally an initiative of the US military. Even then, CNC mills and other computer-aided manufacturing machines were used in the construction of military aircraft. In addition, CAD software was used early on to develop components. At that time, however, the CAD programs all generated their own file formats, which were not compatible with each other. The programs were also unable to automatically output CNC-compatible data. The main goal of the IGES initiative was therefore to develop a common standard that would allow CAD blueprints to be converted into a format that could be used by CNC machines.

Based on conversion software developed by aircraft manufacturer Boeing, development of the IGES format began in 1978. Since the U.S. military relied heavily on the new format, IGES became the de facto standard for CNC data in the following years, especially in the military sector. In the mid-1980s, STEP was launched as a successor. The ISO-standardized newer format replaced IGES in almost all areas from the 1990s onwards, so that today the file format is only found in modern CAD programs for reasons of downward compatibility.

Use of the IGES file today

IGES no longer plays a major role today in the shadow of the more modern STEP format. However, since CNC machines that could only read IGES files were still used for a long time, many companies and research institutions still have a lot of data in IGES format only. Fortunately, CAD and comparable programs continue to support the format, so that the gradual conversion of old data sets is not a problem.

Structure of the IGES file formats

The IGES file is stored as plain text readable ASCII files. In principle, there is also a binary coded format variant, but this has never been widely accepted. An IGES file consists of 80 character long lines. This somewhat unusual line length goes back to earlier punch card formats, which often had exactly this length.

The lines of an IGES file represent five separate sections. Start, Global, Directory Entry, Parameter Data and Terminate.

• The Start and Terminate sections usually contain only one line each and are mainly used by the parser for orientation.
• The Global section contains meta information like the used IGES version or the title of the build plan.
• The actual build plan information is encoded in the Directory Entry and Parameter Data areas.

In the Directory Entries, primitives such as points, lines or circles are defined and, if necessary, linked to so-called entities that can be used to describe the logical structure of the blueprint. In addition, information such as the color of an element can be defined. When describing surfaces, it is also possible to specify whether the surface is an exterior or interior surface. Precise vector data and coordinates are then entered in the parameter data area of the file for all primitives used. The logic of the design is thus clearly separated from the placement of the elements on the digital drawing board.

FAQ about IGES files:

What is the difference between .IGS and .STP files?

STEP files (most common extension .stp) are the successor format to the IGES standard that has been in use since the 1990s. STEP stands for Standard for the exchange of product model data. The name already indicates that the format can do a bit more than a simpler IGES file. The standard defined in ISO standard 10303 not only has the task of storing the construction plan of a product. In addition, it is also intended to help prepare information about the object or product in databases.

Can I convert .IGS and .STP files into each other?

Yes, in principle it is possible to convert both formats into each other. However, it should be noted that information may be lost when converting STEP to IGES. Conversely, STEP files generated from IGES data are usually less informative than natively developed STEP data. Other conversions such as STL to IGES are also possible.

Which programs support the IGES format?

Almost all modern CAD programs still offer the possibility to import and export IGS files. However, for the practical use of all functions offered by the programs, the file format, which is now somewhat outdated in many respects, is not suitable. For the processing of construction plans, it is usually more sensible to rely on the native formats of the respective software. In addition to CAD applications such as AutoCAD or TurboCAD, there are also pure IGS viewers such as the program ABViewer, with which IGS construction plans can be opened and viewed quickly and easily. However, editing or converting the data is typically not possible with such viewers.

Is the IGES format open?

The definitions of the IGES format are completely open. You can use the file format in your own software projects without paying any license fees.