3D File Format For Long Term Storage

When Adobe added 3D to PDF they hoped that CAD users would start using 3D PDF as a data exchange and storage format, instead of IGES and STEP or some CAD vendors proprietary format like Parasolid, JT, etc. To aid the adoption of 3D PDF Adobe decided to make it a truly open standard by making it an ISO standard. In a post titled “PDF To Wear The ISO Hat” that I published here back in December 2007 I wrote:

“Adobe is supposed to have converted the PDF 1.7 Reference into an ISO Draft by removing all Adobe and Acrobat specific information. Once PDF becomes an ISO standard, Adobe will be just one of many implementers of that standard.”

I have been talking to Visual Technology Services, a UK based company which is another implementer of the PDF standard besides Adobe. They have developed a C++ 3D PDF authoring  library called PDF3D SDK aimed at CAD software developers who wish to add 3D PDF publishing capability to their products. They also have an end user product called PDF3D ReportGen and some plug-ins to create 3D PDF files. Today Visual Technology Services issued a press release announcing compatibility of their technology with the latest version of Adobe Reader X including PRC (Product Representation Compact) encoding for 3D models. This proves that PDF is truly an open standard.

I often get asked this question, “What 3D file format should I use to for long term storage of my 3D CAD data?” My answer always is “3D PDF or 3DM“.


Even if Adobe disappears or is bought by a company like Enron or does something stupid (see “The Adobe 3D PDF Train Wreck“), the latter being the one with the highest probability, there will always be a way to get access to your 3D data since PDF is now a truly open ISO standard (ISO 32000-1:2008). The PDF file format specification is out there for everyone to see. Visual Technology Services made use of the ISO PDF spec document to create their own 3D PDF library and end user software.

This is probably one of the reasons huge companies like Boeing have invested heavily into 3D PDF. These companies need to be sure that they will continue to have access to their data 50 years from today. Some people use IGES and STEP to store their data for the long term. I hope you don’t. And if you absolutely had to choose between the two I would recommend STEP over IGES. Over the years CAD vendors have abused the IGES file format by making variants of it to suit their specific needs, thereby defeating the very purpose of a neutral standard. One look at the Rhinoceros IGES export options dialog box gives you an idea of the magnitude of the problem.

There are 60 types of “standard” IGES files and I’m sure more will be added in time. Alibre has created its own flavor of the STEP file format to store certain parameters. I’m not sure whether any other CAD vendors have done something similar. It looks like STEP is going down the path of IGES. While these CAD vendors may have the best of intentions it really does not help creating different flavors of a neutral file format. Having variants of a standard is it itself an oxymoron.


What Adobe did with PDF is truly commendable. They took their PDF proprietary file format and gave it to ISO to make it an open standard. McNeel did something even more commendable with Rhinoceros by giving away the source code of their 3DM read/write library through the OpenNURBS Initiative. As a programmer if I want to write software to read or write a 3DM file I do not need to read some 3DM file format specification and cook up the source code for it. I simply use the source code  given by McNeel. In fact that is precisely what we do at SYCODE. Many times, when our data exchange products convert a 3D CAD file from one format to another we use 3DM as an intermediate format. For us, 3DM is a truly open standard 3D file format.

There are other open or semi-open formats as well. Autodesk’s DWF is one example. But 3D PDF and 3DM are the ones I recommend the most. The only reason I put 3D PDF over 3DM is because the future of PDF is not guided by a single entity or company. If something is to be made a standard it not only needs to be used by many people. It should also be developed and driven by many people.

Proprietary Standards

The problem with many CAD vendors and their “propreitary standard” formats is that they want to keep total control over them with the result that they becomes a standard for themselves and those in their ecosystem only. Take JT from Siemens PLM for example. First of all you need to pay Siemens PLM an initial membership fee plus an annual maintenance fee to get into their JTOpen program. And to make it worse, these fees are calculated on your annual revenue. There’s more. If you use their software to develop in-house software or software that you share with “corporate” members of the JTOpen program, you are good. Otherwise you need to pay Siemens PLM royalty. I often refer to JT as “Just Talk” because Siemens PLM’s interest in JT is more about earning revenue from it and less about solving the data exchange problem of the CAD software industry.

What’s your 3D file format for long term storage? Do you think about long term storage in the first place?