A mathematical model is presented for comparing geometric and image-based simplification methods. Geometric simplification reduces the number of polygons in the virtual object and image-based simplification replaces the object with an image. Our model integrates and extrapolates existing accuracy estimates, enabling the comparison of different simplification methods in order to choose the most efficient method in a given situation. The model compares data transfer and rendering load of the methods. Byte size and expected lifetime of simplifications are calculated as a function of the desired visual quality and the position and movement of the viewer. An example result is that, in typical viewing and rendering conditions and for objects with a radius in the order of one meter, imposter techniques can be used at viewing distances above 15 meters. Below that, simplified polygon objects are required and, below one meter distance, the full-resolution virtual object has to be rendered. An electronic version of the model is available on the web.

To support 3D GIS interaction within VR-environments we propose a multi-view approach based on three types of visualization: plan view, model view and world view. The visualization in these views ranges from a conventional map, through a partly symbolic and simplified 3D representation to a full immersive and photo-realistic 3D display. The views can be used simultaneously or intermittently, and each provides a repertoire of interaction possibilities that are apt but not necessarily limited to that view. We are currently developing a 3D GIS&VR system (Karma VI) based on existing GIS and VR technology that uses the three views to support the design, development and presentation of large infrastructure plans in The Netherlands. Operational use of this system showed that the multi-view approach leads to a more sophisticated understanding of those plans.

Abstract Ray tracing algorithms that sample both the light received directly from light sources and the light received indirectly by diffuse reflection from other patches, can accurately render the global illumination in a scene and can display complex scenes with accurate shadowing. A drawback of these algorithms, however, is the high cost for sampling the direct light which is done by shadow ray testing. Although several strategies are available to reduce the number of shadow rays, still a large number of rays will be needed, in particular to sample large area light sources. An adaptive sampling strategy is proposed that reduces the number of shadow rays by using statistical information from the sampling process and by applying information from a radiosity preprocessing. A further reduction in shadow rays is obtained by applying shadow pattern coherence, i.e. reusing the adaptive sampling pattern for neighboring sampling points.

Adaptive stochastic ray tracing is a rendering technique that generates high-quality anti-aliased images by sampling the image in a non-regular pattern that is adaptively refined. Image refinement can be guided by image space or object space criteria. For display of textures, additional criteria that operate in texture space can be added to further improve image quality. In this paper three texture space refinement criteria are introduced. The methods minimize the chance of sampling errors at the cost of only a small amount of preprocessing and are comparable in efficiency with existing texture prefiltering methods.

Constructive Solid Geometry (CSG) defines objects as Boolean combinations (CSG trees) of primitive solids. To display such objects, one must classify points on the surfaces of the primitive solids with respect to the resulting composite object, to test whether these points lie on the boundary of the composite object or not. Although the point classification is trivial compared to the surface classification (i.e., the computation of the composite object), for CSG models with a large number of primitive solids (large CSG trees), the point classification may still consume a considerable fraction of the total processing time. This paper presents an overview of existing and new efficiency-improving techniques for classifying points in depth order. The different techniques are compared through experiments.

An algorithm is presented for constructing shadow volumes for CSG objects. For each primitive solid, the algorithm calculates a tree of shadow volumes to model the shadows generated by the shadow-generating parts of the boundary of the primitive. The shadow of the complete CSG object is the union of these shadow trees. An implementation of the algorithm is described for a scan-line display algorithm for CSG objects with polygonal primitives.

There is a growing need for fast high-quality display of solid objects. Recently-developed custom-VLSI hardware offers high-speed display but lacks the flexibility and processing power at the pixel level to sustain the calculations and filter operations needed for realistic reflection models, texture mapping and anti-aliasing. Multi-processor systems built with general-purpose components of relatively high capacity and moderate cost provide an alternative; they also offer higher performance than single processor systems but retain their flexibility. A CSG hidden-surface algorithm based on depth-buffering and image subdivision is presented which is suitable for use with such a multi-processor system.

VLSI techniques have greatly enlarged the possibilities to design new frame buffer architectures with parallel processing capabilities down to the pixel level. For these pixel processor systems a parallel hidden surface algorithm is presented for displaying objects defined with Constructive Solid Geometry. The algorithm is based on a CSG evaluation with bitwise operations and multiple scanning of the primitives.

Several algorithms exist for visualizing geometric models defined by constructive solid geometry (CSG). Each of these algorithms is based on standard hidden surface methods, such as ray tracing, scan-line and z-buffer algorithms. In this paper a CSG list priority algorithm is described that is combined with a ray tracing algorithm in the use of a spatial subdivision technique and a CSG list structure to exploit CSG coherence. The combined algorithm is designed for interactive viewing and high quality rendering of CSG models with faceted primitives.

Abstract Now that raster graphics has become a common tool in CAD/CAM systems, animation and many other applications, the need has arisen for user interfaces to graphics packages for these new applications. On the basis of a typology of the users, an analysis is presented of some of the choices which have to be made in developing these interfaces.

The long processing times inherent in the use of raster graphics techniques for the shading of complex scenes, complicate the design and debugging of a picture. The efficiency of the picture-generating process can, however, be improved by adding several interactive facilities to the system. In particular, fast previewing techniques are valuable for checking the modeling and for getting a good impression in an early stage of the picture-definition process. A discussion of raster graphics system design is followed by examples of fast pre-viewing techniques for the shading and texture mapping of surface models and for the shading of solid models using a raycasting technique.