Arjan J. F. Kok

Source Selection for the Direct Lighting Computation in Global Illumination

Computation of the global illumination in a scene can be improved by separating the direct component of the lighting, which is received by a patch directly from light sources, from the indirect component, which is received by intermediate interreflection from other patches. The indirect component is calculated during the preprocessing and is stored as the radiosity shading at the patch. The direct component is calculated during the rendering phase by tracing shadow rays like in conventional ray tracing. The number of shadow rays can be reduced by exploiting shadow coherence, and by making a selection for the number of light sources that are taken into account for the direct lighting computation. Different criteria to select these sources are given.

Experiencing 3D interactions in virtual reality and augmented reality

We demonstrate basic 2D and 3D interactions in both a Virtual Reality (VR) system, called the Personal Space Station, and an Augmented Reality (AR) system, called the Visual Interaction Platform. Since both platforms use identical (optical) tracking hardware and software, and can run identical applications, users can experience the effect of the way the systems present their information to them (as VR or AR). Since the systems use state-of-the-art tracking technology, the users can also experience the opportunities and limitations offered by such technology at first hand. Such hands-on experience is expected to enrich the discussion on the role that VR and AR systems (with optical tracking) could and/or should play within Ambient Intelligence.

Adaptive Sampling of Area Light Sources in Ray Tracing Including Diffuse Interreflection

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.

Efficient, complete radiosity ray tracing using a shadow-coherence method

Most two-pass rendering methods calculate a radiosity shading for each patch or element in a scene in the first pass. This shading contains two components: one for the light received directly from the main light sources and one representing the intensity of the light received indirectly by means of diffuse and specular interreflection between patches. However, it is very difficult to achieve accurate representation of the distribution of this radiosity shading over the patch, particularly where clearly visible shadow boundaries exist. A better approach is to store only the indirect reflection component in the form of radiosity shading, and to calculate the direct reflection component during the second pass by casting shadow rays. This approach normally requires that many shadow rays must be cast. However, the number of rays for shadow testing can be kept low by selecting only those light sources that substantially contribute to the shading of a patch and applying an adaptive image refinement technique in combination with a shadow coherence method.

The 3D Object Mediator: Handling 3D Models on Internet

The 3D Object MEdiator (3DOME3) offers two services for handling 3D models: a modelshop and a renderfarm. These services can be consulted through the Internet. The modelshop meets the demands for brokerage of geometric descriptions of 3D models. People who create geometric models of objects can supply their models to the modelshop and 3DOME will offer them to potential customers. People who need models can browse through the model database and buy the models they need. The renderfarm, consisting of a large number of workstations and multiprocessor computers, offers rendering services to generate: animations and realistic images of large scenes. In general, these kinds of renderjobs cannot be done by a single workstation in an acceptable amount of time. 3DOMEs parallel rendering facilities may be very helpful for these jobs.

A Two-Pass Radiosity Method for Bézier Patches

A restriction of the radiosity method has been the difficulty of processing environments consisting of curved surfaces. In order to apply current radiosity methods, such surfaces are usually subdivided into many polygonal patches. However, as the computational complexity of the radiosity method depends on the number of patches, this approach results in a very inefficient use of the available processing time and data storage capacity. In this paper, a ray tracing based radiosity method for diffuse and specular reflective Bezier surfaces is presented. The original Bezier surface description is used throughout the entire algorithm which makes the subdivision of each Bezier patch into many polygonal patches unnecessary.

Hardware challenges for ray tracing and radiosity algorithms

Computer graphics algorithms and graphics hardware have mainly been developed along two lines: real-time display and realistic display. Real-time display has been achieved by developing dedicated hardware for projective, depth-buffer display algorithms. Increased realism has been achieved by ray tracing and radiosity algorithms, which generally are implemented on standard workstations because the complexity of the computation makes it difficult to implement these algorithms in hardware. In this paper we review these different approaches and discuss the feasibility of using special hardware to enhance the radiosity and ray tracing computation. In particular we will explore the use of the intersection of a frustrum of rays with patches in a scene as a basic computational primitive for these algorithms and their implementation in hardware.