Advances in computer graphics in the recent twenty years have stimulated different schemes to classify research directions and systems. In the early days, graphics systems were identified to be vector or raster graphics in terms of technology. Sutherland's Sketchpad system was the first example that allowed to distinguish between passive and interactive computer graphics. Dimensions of the geometric data model classified systems to be a 2D or 3D system. This scheme was used by standardization activities in computer graphics during the last decade. However, the approaches of standard committees to develop a reference model for computer graphics have shown very clearly that the variety of systems and the complexity within one graphics system prevents from the establishment of an easy-to-understand model. Taxonomies in scientific visualization (MzCo-87) focussed on the integration of different disciplines like computer graphics and computer vision, and the use of available, mostly heterog eneous system components and peripherals. At least, scientific visualization has shown very clearly that computer graphics today is very different from drawing and image processing. Our understanding (Felg-90) of scientific visualization comprises outstanding system requirements like: massive amounts of complex and multidimensional data to be processed, peripheral and algorithmic means for interactive data exploration, manifold alternative (physical and logical) visual (but also non-visual) data presentation techniques, and computational models for physical phenomena. Consequently, scientific visualization requires a correspondence between the human perception and the abstract computer-internal representation of the physical world. Visualization in scientific computing needs this correspondence, virtual reality even requires more! Virtual reality presumes integrated presentation, feedback and simulation techniques and demands realtime! Realtime in this context is defined as the evalu
