STEP Files vs. IGES Files

By Clint Brown

I get quite a few enquiries from customers battling with misbehaving IGES files. The issues are generally related to surface models that cannot be stitched together, or models with missing faces. 

I always suggest that people share their native CAD file, or that they use STEP files as an exchange format. Companies tend to use IGES files, simply because they have been around for so long. IGES was the file first format that allowed 3D CAD packages to exchange data. That being said, it is often not the best format for sharing accurate data.

What is an IGES file?

The Acronym IGES, stands for "Initial Graphics Exchange Specification".

IGES evolved from of the U.S. Air Force's Integrated Computer Automated Manufacturing (ICAM) program in 1979. IGES was designed as a neutral format for the exchange of CAD models and was first published in January 1980 by the U.S. National Bureau of Standards as NBSIR 80-1978. The file format can be shown as .igs, .ige or .iges.

The IGES standard was last updated in 1996.

What is a STEP file?

The Acronym STEP, stands for "Standard for the Exchange of Product model data".

The development of STEP started in 1984 as a successor of IGES, but due to the complexity of the project, the initial standard was only published in 1994.  The STEP format conforms to ISO 10303-21. It is constantly updated, with the last major update in 2016. The file format can be shown as .step, .stp, .stpz, .ste or .p21

What's wrong with using IGES files?

Technically there's nothing wrong with using the IGES format, however, IGES files tend to be surface models, and often get translated with gaps between the surfaces, missing faces and in some instances surfaces with faces in the wrong orientation. While there is is an IGES standard for solids (IGES-MSBO), it is not often used. 

When a user creates an IGES file, they are translating their native CAD file into the IGES format. When this file is shared, it is imported into the next CAD package and is translated again. File translations, could potentially bring in inaccuracies in the geometry.

The benefit of using the Native CAD file, is that it only requires 1 translation, which is theoretically more accurate.

Why is STEP better than IGES?

STEP is newer technology, where IGES which is older 1990's technology, that has not been updated in over 20 years. STEP files tend to be solid models, where IGES files are more often surface models, which could have gaps and missing faces.

STEP is a mature file format, it has been available for over 20 years with continual development and wide adoption between CAD vendors.

STEP is widely used, and is even used in the construction industry, the IFC file format is a version of STEP.

For more information on these file formats, check out Lars Christensen's informative video below, which inspired this blog post:

Credits: Wikipedia: IGES, Wikipedia: STEP

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