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Item Improved Sparse Seeding for 3D Electrostatic Field Lines(The Eurographics Association, 2015) Scharnowski, Katrin; Boblest, Sebastian; Ertl, Thomas; E. Bertini and J. Kennedy and E. PuppoWe present an improved seeding strategy for sparse visualization of electrostatic fields. By analyzing the curvature of the field lines, we extract points of extremal field strength between charges of different sign and use them to seed field lines, which consequently connect the corresponding charges. The resulting sparse representation can be seen as an extension to classic vector field topology depicting properties otherwise hidden. Finally, by applying our method to a synthetic data set, we show its benefits over previously published work.Item Evaluation of Visualizations for Interface Analysis of SPH(The Eurographics Association, 2014) Krone, Michael; Huber, Markus; Scharnowski, Katrin; Hirschler, Manuel; Kauker, Daniel; Reina, Guido; Nieken, Ulrich; Weiskopf, Daniel; Ertl, Thomas; N. Elmqvist and M. Hlawitschka and J. KennedyWe present a GPU-accelerated visualization application that employs methods from computer graphics and visualizationto analyze SPH simulations from the field of material science. To this end, we extract the isosurfacethat separates the stable phases in a fluid mixture via the kernel function that was used by the simulation. Ourapplication enables the analysis of the separation process using interactive 3D renderings of the data and an additionalline chart that shows the computed surface area over time. This also allows us to validate the correctnessof the simulation method, since the surface area can be compared to the power law that describes the change inarea over time. Furthermore, we compare the isosurface that is based on the simulation kernel with an establishedmethod to extract smooth high-quality SPH surfaces. The comparison focuses on demonstrating the applicabilityfor data analysis in the context of material science, which is based on the resulting surface area and how wellthe two phases are separated with respect to the original particles. The evaluation was carried out together withexperts in material science.Item Interactive Exploration of Polymer-Solvent Interactions(The Eurographics Association, 2011) Thomaß, Bertram; Walter, Jonathan; Krone, Michael; Hasse, Hans; Ertl, Thomas; Peter Eisert and Joachim Hornegger and Konrad PolthierThe interaction of three-dimensional linked hydrophilic polymers with surrounding solvents in time-dependent data sets is of great interest for domain experts and current research in molecular dynamics. These polymers are called hydrogels, and their most characteristic property is their swelling in aqueous solutions by absorbing the solvent. Their conformation transition can be studied by investigations of the interaction of the single polymer strand and the solvent directly around the polymer at an atomistic level. We present new visualization techniques to interactively study time-dependent data sets from molecular dynamics simulations-with special regard to polymer-solvent interactions like local concentrations and hydrogen bonds-as well as filtering methods to facilitate analysis. Such methods that visualize polymer-solvent interactions on a hydration shell around a polymer are not available in current tools and can greatly facilitate the visual analysis, which helps domain experts to extract additional information about hydrogel characteristics and gain new insights from the simulation results. While our visual analysis methods presented in this paper clearly facilitate the analysis of hydrogels and lead to new insight, the presented concepts are applicable to other domains like proteins or polymers in general that interact with solvents.Item Visual Analysis of Public Transport Vehicle Movement(The Eurographics Association, 2012) Wörner, Michael; Ertl, Thomas; Kresimir Matkovic and Giuseppe SantucciPublic transport vehicles record detailed operational logs. In major networks, this quickly amounts to massive datasets. Traditionally, these are analysed only using statistical tools, yet they show great potential for the successful application of visual analytics techniques and the integration of different visualizations in order to improve service quality and passenger comfort. We present a visual analytics tool for the analysis of such data and apply it to a real-world dataset of actual public transport vehicle movements.Item Voronoi-Based Foveated Volume Rendering(The Eurographics Association, 2019) Bruder, Valentin; Schulz, Christoph; Bauer, Ruben; Frey, Steffen; Weiskopf, Daniel; Ertl, Thomas; Johansson, Jimmy and Sadlo, Filip and Marai, G. ElisabetaFoveal vision is located in the center of the field of view with a rich impression of detail and color, whereas peripheral vision occurs on the side with more fuzzy and colorless perception. This visual acuity fall-off can be used to achieve higher frame rates by adapting rendering quality to the human visual system. Volume raycasting has unique characteristics, preventing a direct transfer of many traditional foveated rendering techniques. We present an approach that utilizes the visual acuity fall-off to accelerate volume rendering based on Linde-Buzo-Gray sampling and natural neighbor interpolation. First, we measure gaze using a stationary 1200 Hz eye-tracking system. Then, we adapt our sampling and reconstruction strategy to that gaze. Finally, we apply a temporal smoothing filter to attenuate undersampling artifacts since peripheral vision is particularly sensitive to contrast changes and movement. Our approach substantially improves rendering performance with barely perceptible changes in visual quality. We demonstrate the usefulness of our approach through performance measurements on various data sets.Item Interactive CPU-based Ray Tracing of Solvent Excluded Surfaces(The Eurographics Association, 2019) Rau, Tobias; Zahn, Sebastian; Krone, Michael; Reina, Guido; Ertl, Thomas; Kozlíková, Barbora and Linsen, Lars and Vázquez, Pere-Pau and Lawonn, Kai and Raidou, Renata GeorgiaDepictions of molecular surfaces such as the Solvent Excluded Surface (SES) can provide crucial insight into functional molecular properties, such as the molecule's potential to react. The interactive visualization of single and multiple molecule surfaces is essential for the data analysis by domain experts. Nowadays, the SES can be rendered at high frame rates using shader-based ray casting on the GPU. However, rendering large molecules or larger molecule complexes requires large amounts of memory that has the potential to exceed the memory limitations of current hardware. Here we show that rendering using CPU ray tracing also reaches interactive frame rates without hard limitations to memory. In our results large molecule complexes can be rendered with only the precomputation of each individual SES, and no further involved representation or transformation. Additionally, we provide advanced visualization techniques like ambient occlusion opacity mapping (AOOM) to enhance the comprehensibility of the molecular structure. CPU ray tracing not only provides very high image quality and global illumination, which is beneficial for the perception of spatial structures, it also opens up the possibility to visualize larger data sets and to render on any HPC cluster. Our results demonstrate that simple instancing of geometry keeps the memory consumption for rendering large molecule complexes low, so the examination of much larger data is also possible.Item Interactive High-Quality Visualization of Higher-Order Finite Elements(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ueffinger, Markus; Frey, Steffen; Ertl, ThomasHigher-order finite element methods have emerged as an important discretization scheme for simulation. They are increasingly used in contemporary numerical solvers, generating a new class of data that must be analyzed by scientists and engineers. Currently available visualization tools for this type of data are either batch oriented or limited to certain cell types and polynomial degrees. Other approaches approximate higher-order data by resampling resulting in trade-offs in interactivity and quality. To overcome these limitations, we have developed a distributed visualization system which allows for interactive exploration of non-conforming unstructured grids, resulting from space-time discontinuous Galerkin simulations, in which each cell has its own higher-order polynomial solution. Our system employs GPU-based raycasting for direct volume rendering of complex grids which feature non-convex, curvilinear cells with varying polynomial degree. Frequency-based adaptive sampling accounts for the high variations along rays. For distribution across a GPU cluster, the initial object-space partitioning is determined by cell characteristics like the polynomial degree and is adapted at runtime by a load balancing mechanism. The performance and utility of our system is evaluated for different aeroacoustic simulations involving the propagation of shock fronts.Item Interactive Hierarchical Quote Extraction for Content Insights(The Eurographics Association, 2019) Knittel, Johannes; Koch, Steffen; Ertl, Thomas; Madeiras Pereira, João and Raidou, Renata GeorgiaThis work presents a new approach to visually summarize large micro-document collections such as tweets. We extract frequent patterns of phrases as shortened quotes to present analysts an overview of popular snippets and statements, enabling more specific insights into large text collections compared to keyword-based visualizations. In our hierarchical structure, each quote can be the starting point to extract more fine-grained patterns on a subset of sentences that match the parent pattern. We show that our approach is scalable by applying it to millions of tweets.Item Coherent Culling and Shading for Large Molecular Dynamics Visualization(The Eurographics Association and Blackwell Publishing Ltd., 2010) Grottel, Sebastian; Reina, Guido; Dachsbacher, Carsten; Ertl, Thomas; G. Melancon, T. Munzner, and D. WeiskopfMolecular dynamics simulations are a principal tool for studying molecular systems. Such simulations are used to investigate molecular structure, dynamics, and thermodynamical properties, as well as a replacement for, or complement to, costly and dangerous experiments. With the increasing availability of computational power the resulting data sets are becoming increasingly larger, and benchmarks indicate that the interactive visualization on desktop computers poses a challenge when rendering substantially more than millions of glyphs. Trading visual quality for rendering performance is a common approach when interactivity has to be guaranteed. In this paper we address both problems and present a method for high-quality visualization of massive molecular dynamics data sets. We employ several optimization strategies on different levels of granularity, such as data quantization, data caching in video memory, and a two-level occlusion culling strategy: coarse culling via hardware occlusion queries and a vertex-level culling using maximum depth mipmaps. To ensure optimal image quality we employ GPU raycasting and deferred shading with smooth normal vector generation. We demonstrate that our method allows us to interactively render data sets containing tens of millions of high-quality glyphs.Item Direct Visualization of Particle-Partition of Unity Data(The Eurographics Association, 2011) Üffinger, Markus; Schweitzer, Marc Alexander; Sadlo, Filip; Ertl, Thomas; Peter Eisert and Joachim Hornegger and Konrad PolthierDirect visualization of higher-order data provides manifold advantages over the traditional approach, which is based on resampling and subsequent visualization by interpolation-based techniques. Most important, it avoids excessive computation and consumption of memory, and prevents artifacts by pixel-accurate visualization at interactive rates. This work addresses particle-partition of unity simulation data, where fields are modeled both using cell-based analytic representations together with enrichment functions centered at individual points. This combination of bases allows for superior simulation convergence rates and is able to capture high field variations with comparably small sets of basis functions. In this paper we propose direct visualization of such data from 2D simulations, providing accurate insight. We additionally visualize solver performance, allowing for more directed simulation design, and exemplify our technique using a GPU-based prototype on crack simulation examples.