many approaches have been performed by first defining the internal model representation, capable of storing geometric, topological and hierarchical dependencies between components in a model. Less attention is paid to the user interface, job completion and to the user's subjective feeling about the tool. In fact, the intention and the actual result are considerably different in most announced VR modelers.
The mainly computer-based development of products offers many advantages regarding optimization of time, costs and quality. But it quickly leads to a restricted, reduced perception of the product during the development process. Digital Mock-Ups (DMU) therefore require VEs so as to improve the perception of the computer-based models respective the product.
Today users can choose from a lot of visualization systems exploiting different concepts. Is it possible to get a general user ranking for the available systems? Three main questions were observed: In which virtual environment can people estimate dimensions more precisely? What subjective competence do users get? Are there significant differences between the visualization systems (CAVETM, HMD, BOOMTM)?
The results in table 1 show that Immersive Projection Technology (IPT) systems (here: CAVETM) are most appropriate for DMU. An important advantage is the possibility for natural user co-operation. IPT systems provide a natural overlay of computer generated virtual space and the true physical space including the user's own body. This mix of real and virtual space is very expensive to achieve the use of systems like HMD or BOOM. A very important fact is the awareness