Don't Get Lost in CAD-to-BIM Translation

8 Feb, 2011 By: Robert Green

Get everyone on the same page by mapping out the inputs and outputs for your next project — in very specific terms.

In the last edition of the CAD Manager's Newsletter, I opined that translating CAD geometry between BIM (building information modeling) and traditional CAD systems would become an increasingly common challenge for CAD managers. I've heard from a number of readers that they're struggling with this task, and would like some advice on how to deal with it.

In this edition of the newsletter, I'll give you an approach to translating that will work regardless of which CAD formats you use in-house or interact with outside your company. Along the way, I'll point out some action items for you and your company's project manager. Here goes.

Clarify Project Requirements — in Writing

Let's say that you're embarking on a new project that will require you to submit BIM information. Questions abound: What BIM software package will that be — and which version? Will you be required to create floor plans in separate 2D files? Will you need to provide files to government agencies in other formats? Will you need to archive plots using PDF or other raster formats? These are the questions that need to be answered and nailed down with specifics now, so nobody is surprised later.

And as you think about which file formats you'll need to supply, don't forget that over the duration of a multiyear project your software tools may have one or more major updates. This possibility makes it all the more important that clients specify the version of any file formats required. So do not accept, for example, that you'll deliver 2D files in AutoCAD format — instead, specify that you'll supply AutoCAD Architectural 2010 DWG-formatted files.

Finally, I can't stress enough that if it isn't written down, it doesn't count. At the end of the project you'll be required to provide digital information to your client based on the written requirements in the contract. If the contract simply says "Supply all information in BIM," then what "BIM" means is totally open to interpretation. My experience has shown that open interpretations lead to misunderstandings, hard feelings, and lawsuits — and nobody wants those.

Action item for CAD manager: Work with your project managers and the client to determine what specific CAD requirements must be met and how much CAD time is required.

Action items for project manager: Make sure that the specific requirements are included in the project contracts and that enough CAD operator hours are included in the project scope to meet the requirements.

Know Your Inputs, Tools, and Outputs

For the purposes of our discussion, I'm going to define "CAD input" as a file you receive and must import in order to work with it. Likewise, I'll define "CAD output" as a file you produce to send to another user, department, vendor, or client. The "tools" part of the equation refers to the software you use in-house for your project design.

To get organized, I will create a brief list to describe the inputs, tools, and outputs I will deal with during my project work, along with a brief description of how each will be used. Here's an example, based on an architectural and landscaping renovation to an office site.


  • Microstation V8.1 DGN files (civil site plans with roads from last landscape update)
  • AutoCAD 2007 DWG files (2D building plans from last architect update).

In-house tools:

  • Revit Architectural 2010 files (used for building design)
  • Revit Structural/MEP 2010 (for load, HVAC, and plumbing revisions).


  • Revit Architectural 2010 files (building model sent to client)
  • AutoCAD 2010 DWG files (for 2D building plans sent to client)
  • Microstation V8i DGN files (sent to local permitting agency for road changes)
  • 24x36 color PDF plots (for print records sent to client).

Looks a little daunting when you list it all out, doesn't it? Hopefully you're focused on addressing translation issues now, to ensure that you won't be unpleasantly surprised later in the project.

Action item for CAD manager: Contact the CAD manager at the client company for help in identifying correct inputs and outputs. Quite often you'll learn more during a 10-minute conversation with the CAD manager than in hours of talking to project managers.

Diagram It

You can now list your inputs, tools, and outputs in flow-chart fashion to visualize the logical process you'll go through to complete your project. It is amazing how much more organized you'll be — and how much more relaxed you'll feel — when every translation requirement is accounted for!

Feel free to expand your diagram to include disk or server storage locations, checking procedures, or any other work or IT factor that affects your translation processes.


Now that you know what all your project requirements are, it is time to do some benchmark testing.

I like to focus my attention on testing my inputs first, because the ability to read these files will be critical at project startup. Quite simply, you want to make sure you can actually read the information you're sent, then work with it in your tools. Document what you learn by keeping good notes; you'll need them later when the project kicks off.

Action items for CAD manager: Request sample input files from the client's CAD manager, making sure to request the files in writing (on paper or by e-mail) so that you have a record of the correspondence. Follow up after testing to confirm proper operation or to request further help if the files are unusable.

Once input testing has been completed, it is time to convert some sample data created with your in-house CAD tools to the output formats the client will require. Take detailed notes on how to generate the files, because it may be months before you'll have to undertake these procedures again.

Action item(s) for CAD manager: Be sure to send sample output files to the client CAD manager (again, do so in writing) and have him or her verify that the files you've sent are acceptable. You should end up with a written record from the client saying the sample files you've sent them will satisfy the project requirements.

Summing Up

Understanding the translation requirements of any project is a task best undertaken early and with precision. By using the approach I've outlined, you're far less likely to be surprised, and far more likely to succeed. Plus, you'll have a great written record of the entire process just in case disagreements arise layer. And believe me when I say that failure to deal with your CAD translation issues at the beginning of a project almost always causes disagreements later.

Until next time.

About the Author: Robert Green

Robert Green

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