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Item Energy Aware Color Sets(The Eurographics Association and Blackwell Publishing Ltd, 2009) Chuang, Johnson; Weiskopf, Daniel; Moeller, TorstenWe present a design technique for colors with the purpose of lowering the energy consumption of the display device. Our approach is based on a screen space variant energy model. The result of our design is a set of distinguishable iso-lightness colors guided by perceptual principles. We present two variations of our approach. One is based on a set of discrete user-named (categorical) colors, which are analyzed according to their energy consumption. The second is based on the constrained continuous optimization of color energy in the perceptually uniform CIELAB color space. We quantitatively compare our two approaches with a traditional choice of colors, demonstrating that we typically save approximately 40 percent of the energy. The color sets are applied to examples from the 2D visualization of nominal data and volume rendering of 3D scalar fields.Item Particle Level Set Advection for the Interactive Visualization of Unsteady 3D Flow(The Eurographics Association and Blackwell Publishing Ltd., 2008) Cuntz, Nicolas; Kolb, Andreas; Strzodka, Robert; Weiskopf, Daniel; A. Vilanova, A. Telea, G. Scheuermann, and T. MoellerTypically, flow volumes are visualized by defining their boundary as iso-surface of a level set function. Grid-based level sets offer a good global representation but suffer from numerical diffusion of surface detail, whereas particlebased methods preserve details more accurately but introduce the problem of unequal global representation. The particle level set (PLS) method combines the advantages of both approaches by interchanging the information between the grid and the particles. Our work demonstrates that the PLS technique can be adapted to volumetric dye advection via streak volumes, and to the visualization by time surfaces and path volumes. We achieve this with a modified and extended PLS, including a model for dye injection. A new algorithmic interpretation of PLS is introduced to exploit the efficiency of the GPU, leading to interactive visualization. Finally, we demonstrate the high quality and usefulness of PLS flow visualization by providing quantitative results on volume preservation and by discussing typical applications of 3D flow visualization.Item Real-Time Advection and Volumetric Illumination for the Visualization of 3D Unsteady Flow(The Eurographics Association, 2005) Weiskopf, Daniel; Schafhitzel, Tobias; Ertl, Thomas; Ken Brodlie and David Duke and Ken JoyThis paper presents an interactive technique for the dense texture-based visualization of unsteady 3D flow, taking into account issues of computational efficiency and visual perception. High efficiency is achieved by a novel 3D GPU-based texture advection mechanism that implements logical 3D grid structures by physical memory in the form of 2D textures. This approach results in fast read and write access to physical memory, independent of GPU architecture. Slice-based direct volume rendering is used for the final display. A real-time computation of gradients is employed to achieve volume illumination. Perception-guided volume shading methods are included, such as halos, cool/warm shading, or color-based depth cueing. The problems of clutter and occlusion are addressed by supporting a volumetric importance function that enhances features of the flow and reduces visual complexity in less interesting regions.Item Shadow Mapping Based on Dual Depth Layers(Eurographics Association, 2003) Weiskopf, Daniel; Ertl, ThomasShadow maps are a widely used means for the generation of shadows although they exhibit aliasing artifacts and problems of numerical precision. In this paper we extend the concept of a single shadow map by introducing dual shadow maps, which are based on the two depth layers that are closest to the light source. Our shadow algorithm takes into account these two depth values and computes an adaptive depth bias to achieve a robust determination of shadowed regions. Dual depth mapping only modifies the construction of the shadow map and can therefore be combined with other extensions such as filtering, perspective shadow maps, or adaptive shadow maps. Our approach can be mapped to graphics hardware for interactive applications and can also be used in high-quality software renderers.Item GPU-Based Nonlinear Ray Tracing(The Eurographics Association and Blackwell Publishing, Inc, 2004) Weiskopf, Daniel; Schafhitzel, Tobias; Ertl, ThomasIn this paper, we present a mapping of nonlinear ray tracing to the GPU which avoids any data transfer back to main memory. The rendering process consists of the following parts: ray setup according to the camera parameters, ray integration, ray-object intersection, and local illumination. Bent rays are approximated by polygonal lines that are represented by textures. Ray integration is based on an iterative numerical solution of ordinary differential equations whose initial values are determined during ray setup. To improve the rendering performance, we propose acceleration techniques such as early ray termination and adaptive ray integration. Finally, we discuss a variety of applications that range from the visualization of dynamical systems to the general relativistic visualization in astrophysics and the rendering of the continuous refraction in media with varying density.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and RealismItem Efficient and Adaptive Rendering of 2-D Continuous Scatterplots(The Eurographics Association and Blackwell Publishing Ltd., 2009) Bachthaler, Sven; Weiskopf, Daniel; H.-C. Hege, I. Hotz, and T. MunznerWe extend the rendering technique for continuous scatterplots to allow for a broad class of interpolation methods within the spatial grid instead of only linear interpolation. To do this, we propose an approach that projects the image of a cell from the spatial domain to the scatterplot domain. We approximate this image using either the convex hull or an axis-aligned rectangle that forms a tight fit of the projected points. In both cases, the approach relies on subdivision in the spatial domain to control the approximation error introduced in the scatterplot domain. Acceleration of this algorithm in homogeneous regions of the spatial domain is achieved using an octree hierarchy. The algorithm is scalable and adaptive since it allows us to balance computation time and scatterplot quality. We evaluate and discuss the results with respect to accuracy and computational speed. Our methods are applied to examples of 2-D transfer function design.Item GPU-assisted Multi-field Video Volume Visualization(The Eurographics Association, 2006) Botchen, Ralf P.; Chen, Min; Weiskopf, Daniel; Ertl, Thomas; Raghu Machiraju and Torsten MoellerGPU-assisted multi-field rendering provides a means of generating effective video volume visualization that can convey both the objects in a spatiotemporal domain as well as the motion status of these objects. In this paper, we present a technical framework that enables combined volume and flow visualization of a video to be synthesized using GPU-based techniques. A bricking-based volume rendering method is deployed for handling large video datasets in a scalable manner, which is particularly useful for synthesizing a dynamic visualization of a video stream. We have implemented a number of image processing filters, and in particular, we employ an optical flow filter for estimating motion flows in a video. We have devised mechanisms for combining volume objects in a scalar field with glyph and streamline geometry from an optical flow. We demonstrate the effectiveness of our approach with example visualizations constructed from two benchmarking problems in computer vision.Item 2008 Eurographics Symposium on Parallel Graphics and Visualization(The Eurographics Association and Blackwell Publishing Ltd, 2008) Weiskopf, DanielItem Geo-Spatial Context-Aware Visualization(The Eurographics Association, 2009) Weiskopf, Daniel; D. Ebert and J. KrügerMobile computer systems equipped with wireless communication and sensor technology-such as mobile phones with cameras-have become widely available. Context information, for example the user's current location or their physical environment, plays an increasingly important role in simplifying the interaction between users and such mobile information systems. A generic framework for federating heterogeneous spatial context models is briefly described. The federated information serves as basis for the visualization of spatially referenced data. Visualization challenges include efficient rendering on mobile devices, automatic adaptation of visualization techniques to context information, as well as consideration of the quality of context in the form of uncertainty visualization.Item Flow Visualization by Texture Advection(Eurographics Association, 2003) Weiskopf, Daniel• Vector field visualization: indirectly by tracing particles • Issues: – Seed point positioning – Dense vs. sparse representation – Steady vs. unsteady flow fields – Visualization speed