Cadalyst AEC Tech News #111 (December 18, 2003)

18 Dec, 2003 By: Michael Dakan

In This Issue: Using BIM Information

What Can You Do with BIM?

  • Data Extraction
  • Cost Estimates

How BIM Is Being Used

There is much interest in building information modeling (BIM), and people are wondering whether it's worth the time, effort, and dollars it takes to implement and use it, and what they can do with the model once they create it. When people wonder about the state of BIM today and ask me to comment on whether it's worth it or not, I like to try to find out why they are interested in BIM and what their expectations are about using it.  


DATA EXTRACTION. The ability to do certain kinds of data extraction has been a part of CAD for a long time. It's easy enough to do simple floor area takeoffs, for instance, and linking this information to a spreadsheet or database is pretty straightforward. What BIM tools add to the mix are more sophisticated and simple ways to filter and sort information so that you can do automated takeoffs, say, by department or type of space or based on other criteria that you can set up.

COST ESTIMATES. BIM developers and marketers have talked a lot about the potential for automatic cost estimates, and some demonstration applications have been put together that link BIM data to standard computerized cost estimating tools. Certainly, such things are possible and may become common in the future.

Cost estimating is a good example of the use of data you can add to the model, at least theoretically. But it also illustrates some of the difficulties involved in fully using the data that you can add. For a cost estimate to be accurate and complete enough to be useful, the model also needs to be complete in terms of model structure and cost information. All the elements of the model must be done using intelligent AEC objects that have accurate cost data within the definition of the object. You must add cost information to the AEC objects and keep it current and accurate.

Ideally, it should be possible to predefine all the AEC objects that you might need to complete a model of anything you could conceivably design, but we're still a ways away from being able to do that using only intelligent AEC objects. The BIM tools are not yet developed to the point where all the elements of any conceivable model can be created using only AEC objects. It's still necessary to occasionally use older, more basic 3D elements, such as solids primitives, to complete just the 3D aspects of the model. In some cases, it may even be most expedient to drop back to basic 2D CAD lines, arcs, and circles to complete a 2D drawing extracted from the model.

SPECIFICATIONS: Specification information can also be attached to intelligent AEC objects, but as with cost estimating, the model must be complete and built entirely from intelligent objects in order for it to be able to generate complete construction specifications usable for contract specs. The correct material must be indicated, and any associated specification information must be maintained and kept current and accurate for each project.

Cost and specification information may change significantly from one project to the next. In any case, it would be difficult to predefine AEC objects using all the possible materials and conditions an architect may want to use. Maintaining and keeping current any information that may be attached to AEC objects is a daunting prospect, and most likely will have to be done for each project. This is especially important for cost information in volatile building materials markets such as lumber and steel.


Many people seem to still equate BIM mostly with 3D CAD, and they are not currently interested in too much beyond that, although they may be thinking about other uses for data that can be associated with the model. Of those who have implemented BIM, most seem to be doing very little beyond incomplete 3D modeling and using that to generate 2D drawings. Many users have implemented only what they perceive to be the most useful subset of the complete toolkit. They seem to be content with that, although they may be doing some limited experimentation with using it for nongraphic data uses.

My belief is that the automated building tools for constructing a 3D model, and the ability to generate even incomplete 2D drawings from the model can be enough to justify the use of these tools. Any additional potential uses can be seen as gravy for the future. It's a good idea to start getting familiar with a range of tools and uses for CAD data that you will undoubtedly use more as time goes on.

AutoCAD Tips!

Lynn Allen

Autodesk Technical Evangelist Lynn Allen guides you through a different AutoCAD feature in every edition of her popular "Circles and Lines" tutorial series. For even more AutoCAD how-to, check out Lynn's quick tips in the Cadalyst Video Gallery. Subscribe to Cadalyst's free Tips & Tools Weekly e-newsletter and we'll notify you every time a new video tip is published. All exclusively from Cadalyst!
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