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Item GPU Ray-Casting for Scalable Terrain Rendering(The Eurographics Association, 2009) Dick, Christian; Krüger, Jens; Westermann, Rüdiger; D. Ebert and J. KrügerWith the ever increasing resolution of scanned elevation models, geometry throughput on the GPU is becoming a severe performance limitation in 3D terrain rendering. In this paper, we investigate GPU ray-casting as an alternative to overcome this limitation, and we demonstrate its advanced scalability compared to rasterization-based techniques. By integrating ray-casting into a tile-based GPU viewer that effectively reduces bandwidth requirements in out-of-core terrain visualization, we show that the rendering performance for large, high-resolution terrain fields can be increased significantly. We show that a screen-space error below one pixel permits piecewise constant interpolation of initial height samples. Furthermore, we exploit the texture mapping capabilities on recent GPUs to perform deferred anisotropic texture filtering, which allows for the rendering of digital elevation models and corresponding photo textures. In two key experiments we compare GPU-based ray-casting to a rasterizationbased approach in the scope of terrain rendering, and we demonstrate the scalability of the proposed ray-caster with respect to display and data resolution.Item A Hybrid GPU Rendering Pipeline for Alias-Free Hard Shadows(The Eurographics Association, 2009) Hertel, Stefan; Hormann, Kai; Westermann, Rüdiger; D. Ebert and J. KrügerWe present a new GPU pipeline for rendering per-pixel exact shadows that are cast by point lights and parallel lights. Our approach is hybrid in that it uses kD-tree accelerated ray-tracing to determine shadow-ray intersections, and rasterization to effectively reduce both the number of shadow rays to be traversed and the number of sub-spaces to be considered along each of these rays. To achieve this we introduce conservative shadow maps, which store a conservative estimate of the first intersection with the scene for each possible shadow ray. A novel approach to build such a map is presented, which uses rasterization to compute for every shadow-map pixel the triangles intersecting this pixel. By exploiting the rasterization capacities of recent GPUs in combination with accurate ray-triangle intersection tests, we are able to efficiently compute alias-free shadows in high-resolution and spatially extended scenes where classical shadow mapping techniques have severe difficulties.