Everything You Always Wanted to Know . . . Model Formats

Chapter 7: Digital Model Formats - The Many Flavors of 3D CAD

We’re going to take a little pause in our Everything You Always Wanted to Know About 3D discussion. We’ve talked about the many things you can do with a CAD model but that can lead to some questions. How can I use an OBJ file and how is it different from an STL? Can an IGES and a STEP file essentially be used for the same thing?

These are what we call the “Flavors” of CAD and we’re here to provide you with a short list to help clear up some details.

The Various CAD Flavors:

* ASCII (or ASC) – an X,Y,Z point cloud file in ascii text format.
* DWG - This is a native AutoCad drawing file
* DXF – “Drawing Interchange File” - a neutral version of a DWG file
* IGES – “Initial Graphics Exchange Specification” - a neutral format for exchanging CAD data between many different software programs
* OBJ – an open data format that represents the vertices of polygons
* PRT – a native CAD format for Pro/ENGINEER and NX (Unigraphics)
* SLDPRT – a native CAD format for SolidWorks
* STEP – "Standard for the Exchange of Product model data," (ISO 10303) an advanced neutral format for exchanging CAD data between many different software programs.
* STL – “Standard Tessellation Language” - a polygonal model format similar to OBJ and several others
* WRL (VRML) – “Virtual Reality Modeling Language,” a polygonal file similar to OBJ, STL and several others and can include color
* X_T - a semi-neutral CAD format

Wikipedia also maintains an extensive list of CAD file formats that might be of further interest.

Neutral Formats:

From the list above you’ll notice that some CAD formats are considered neutral, specifically IGES and STEP formats. These two formats were specifically created to neutrally exchange 3D CAD data across different CAD packages.

IGES was created in 1979 by a group of users (including Boeing and GE) with support from the Department of Defense (DoD) and NIST to exchange data more easily. Since the late 80’s the DoD has required that all Digital Project Manufacturing Data (PMI) be deliverable in IGES format.

STEP is an ISO standard released in 1994 to be the “successor” to IGES. While widely used it has never totally replaced the IGES format.

Extra Flavors:

While the above examples are standard across CAD packages, many industries, such as Architecture and 3D modeling for computer graphics have their own packages and files types. We like to think of these as extra flavors, like CAD dessert.

3D Graphics – 3D graphics formats are generally proprietary according to package. Some popular graphics programs are, 3D Studio Max, Maya and Lightwave. Popular gaming companies such as Blizzard Entertainment and other film studios often develop their own in-house formats. However, many consumer 3D graphics packages can import OBJ files.

3D Modeling for Architecture – A new style of modeling for facilities, such as buildings and processing plants, is developing rapidly. This new CAD software contains a relational database component to store metadata for the design entities, such as the style and make of windows or doors, or the schedule of the I-beams and piping. This new class of software is termed BIM for Building Information Modeling and is working to combine facilities management into the database concept as well.

The above list is just a small taste when it comes to the variations of CAD, but they are the most common files used. If you have any questions you should just ask your 3D service provider and they will be happy to help. You can always ask us questions at info@dirdim.com.

The next post in this on-going series will feature a more in-depth discussion and examples of using 3D data for various types of visualization. Stay tuned!