Vol. XII, No. 3
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Winter, 2000

Virtual Reality and CAD - Complementary or Competing?

The differences between Virtual Reality (VR) programs and computer-aided design (CAD) software are often ill-understood. Many people associate VR with games and the most compellingly real presentations of physical settings available with computers. CAD, on the other hand, is associated with architectural and engineering drawings. VR is often thought to refer to more realistic-looking models, CAD to more accurate and precise ones.

In fact, though, CAD and VR are complementary technologies. VR models may be stunningly realistic, but so may CAD models. CAD models may be geometrically accurate and precise, but so may VR models. The distinction between the two technologies has less to do with what kinds of models may be used and more to do with the programs' best features. CAD was developed to create mathematically precise models, in three dimensions, of real-world physical objects. Eventually CAD programs included visualization features, and renderings of astonishing verisimilitude could be created. Nonetheless, the core duty of the software is model creation.

VR systems are most effective at providing the nearest possible experience to being in a physical setting while actually looking only at a computer-generated image, whether a large computer screen or a head-mounted display offering binocular vision. Those VR systems can be used to create models, but their uniqueness and value lie in their ability to display models well and with real-time movement permitted.

CAD programs were created for building models. VR programs are most adept at displaying models. Although each has adopted some of the capabilities of the other, neither is meant to replicate all the functions of the other.

This distinction between CAD and VR is important, because more and more people are thinking seriously about the potential of VR to display important monuments of our past. In fact, at last fall's meeting of the European Association of Archaeologists in Bournemouth, England, there were some interesting displays of VR and some very interesting plans for VR projects. However, few of the presenters demonstrated an awareness of the distinction between CAD and VR software. If VR programs were used at all, VR was taken to be the only tool - for creating the model as well as viewing it. While some VR systems can be used to create good models, CAD systems are easier to use for precise and accurate models, and they are more efficient. In addition, CAD models are better suited, at least at this time, to information retrieval (dimensions and connected tabular data), and CAD data segmentation (discussed elsewhere in this issue, "CAD Data Segmentation - A Crucial Tool,") adds enormous analytic potential.

By the same token, it is true that CAD systems, though they can produce excellent renderings, cannot immerse a user in a virtual world. They cannot present a model as if it were a tangible physical reality. (One of the presentations in Bournemouth was particularly impressive in that regard, showing one of the Dunhuang caves in superb detail. This was a project of the Fraunhofer Institute for Computer Graphics in Darmstadt; the presentation was by Matthias Unbescheiden.)

Ideally, CAD programs should be used to create the models; VR programs should be used to display them. In that way the strengths of both systems can be brought to bear on the creation of good, accurate, precise virtual worlds.

There is an important impediment to the complementary use of CAD and VR. CAD programs write files in formats created for those programs and not for VR. VR programs, on the other hand, use different file formats. While some CAD formats can be translated into some VR formats, what is needed is a more useful file format (or formats) that would permit work on the file in a CAD environment and display of the same file in a VR environment. Then and only then, can changes made in the CAD model be reflected in the VR presentation without requiring the file(s) to be translated from one format to another every time a change is made.

It must be said that, in the very long term, VR may subsume CAD. It may be possible to build a model in a VR world, that is to work within a VR world to create the model, using VR technology to operate the computer. Many see that as the endpoint for VR - making a virtual environment in which computing will take place without requiring users to use current data entry procedures. Instead, one might "draw" or manipulate objects in a virtual 3D world to create a new model. Such a process may be available to model-makers in due course. For now, however, VR is a display technology looking for data to display, and CAD is a data-creation technology looking for better display possibilities. An ideal marriage waiting for the matchmaker.

For other Newsletter articles concerning the applications of CAD modeling in archaeology or uses of electronic media in the humanities consult the Subject index.

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