EG2010
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Item Using VisTrails and Provenance for Teaching Scientific Visualization(The Eurographics Association, 2010) Silva, Cláudio T.; Anderson, Erik; Santos, Emanuele; Freire, Juliana; L. Kjelldahl and G. BaronoskiOver the last 20 years, visualization courses have been developed and offered at universities around the world. Many of these courses use established visualization libraries and tools (e.g., VTK, ParaView, AVS, VisIt) as a way to provide students a hands-on experience, allowing them to prototype and explore different visualization techniques. In this paper, we describe our experiences using VisTrails as a platform to teach scientific visualization. VisTrails is an open-source system that was designed to support exploratory computational tasks such as visualization and data analysis. Unlike previous scientific workflow and visualization systems, VisTrails provides a comprehensive provenance management infrastructure. We discuss how different features of the system, and in particular, the provenance information have changed the dynamics of the Scientific Visualization course we offer at the University of Utah. We also describe our initial attempts at using the provenance information to better assess our teaching techniques and student performance.Item Digitizing Data: Computational Thinking for Middle School Students through Computer Graphics(The Eurographics Association, 2010) Cutler, Robb; Hutton, Michelle; L. Kjelldahl and G. BaronoskiThe concept of digitized data is fundamental to computer science, yet for many students, there is a disconnect between objects they encounter outside the computer and the data they interact with in the computer. A programmingbased approach can exacerbate the problem for young students who are developmentally unready for the abstraction required to translate the world into objects described through the syntax of a programming language. This case study describes the creation of a curricular unit called Digitizing Data, delivered in an eighth grade all-girls computer science class. The unit extends the CS Unplugged Image Representation lesson into a series of coordinated projects, culminating in students using a custom-built application to visualize three-dimensional objects and spaces. The project successfully engaged students in computational thinking, communicated a fundamental computer science topic without the barriers of programming, and allowed them to express computer science concepts creatively.Item A Method for Fast Initialization of Markerless Object Tracking(The Eurographics Association, 2010) Maiero, Jens; Hinkenjann, Andre; Anders Hast and Ivan ViolaIn Mixed Reality (MR) Environments, the user s view is augmented with virtual, artificial objects. To visualize virtual objects, the position and orientation of the user s view or the camera is needed. Tracking of the user s viewpoint is an essential area in MR applications, especially for interaction and navigation. In present systems, the initialization is often complex. For this reason, we introduce a new method for fast initialization of markerless object tracking. This method is based on Speed Up Robust Features and paradoxically on a traditional markerbased library. Most markerless tracking algorithms can be divided into two parts: an offline and an online stage. The focus of this paper is optimization of the offline stage, which is often time-consuming.Item A curvature based lightning model for quasi-global diffuse illumination(The Eurographics Association, 2010) Seipel, S.; Liu, F.; Ericsson, M.; Anders Hast and Ivan ViolaIn this paper we present extensions to local illumination models that take into account light transport and shadowmasking effects in the neighborhood of the surface point under evaluation. Central to our approach is the idea that local curvature represents geometric features in the surrounding neighborhood of this point which have an attenuating or enhancing effect regarding the diffuse illumination of this point. We introduce a lighting model that controls the amount of locally scattered light from the neighborhood based on a local curvature metric. The properties we aim at modeling with this curvature-based illumination model can be found in highly diffuse reflecting materials such as for example snow.Item Hybrid Mesh Editing(The Eurographics Association, 2010) Borosán, Péter; Howard, Reid; Zhang, Shaoting; Nealen, Andrew; H. P. A. Lensch and S. SeipelSurface-based deformation and cage-based deformation are two popular shape editing paradigms. Surface-based methods are easy to use and produce high-quality results by preserving differential properties of the surface mesh, but are limited by their computational requirements. Cage-based methods produce results quickly but at the expense of usability and realism, and typically require manual construction of suitable cages. We introduce a hybrid approach that combines the two methods. The user can perform edits on an automatically-generated simplified version of an input shape using As-rigid-as-possible surface modeling, and the edit is propagated to the original shape by a precomputed space deformation based on Mean value coordinates. We analyze deformation quality and running time for a variety of cage sizes. High-quality results are obtained for meshes on the order of 100K vertices at interactive rates by using cages with app. 5% of the vertices of the original shape.Item Tetrahedral Embedded Boundary Methods for Accurate and Flexible Adaptive Fluids(The Eurographics Association and Blackwell Publishing Ltd, 2010) Batty, Christopher; Xenos, Stefan; Houston, BenWhen simulating fluids, tetrahedral methods provide flexibility and ease of adaptivity that Cartesian grids find difficult to match. However, this approach has so far been limited by two conflicting requirements. First, accurate simulation requires quality Delaunay meshes and the use of circumcentric pressures. Second, meshes must align with potentially complex moving surfaces and boundaries, necessitating continuous remeshing. Unfortunately, sacrificing mesh quality in favour of speed yields inaccurate velocities and simulation artifacts. We describe how to eliminate the boundary-matching constraint by adapting recent embedded boundary techniques to tetrahedra, so that neither air nor solid boundaries need to align with mesh geometry. This enables the use of high quality, arbitrarily graded, non-conforming Delaunay meshes, which are simpler and faster to generate. Temporal coherence can also be exploited by reusing meshes over adjacent timesteps to further reduce meshing costs. Lastly, our free surface boundary condition eliminates the spurious currents that previous methods exhibited for slow or static scenarios. We provide several examples demonstrating that our efficient tetrahedral embedded boundary method can substantially increase the flexibility and accuracy of adaptive Eulerian fluid simulation.Item A Spatially Adaptive Morphological Filter for Dual-Resolution Interface Tracking of Fluids(The Eurographics Association, 2010) Söderström, Andreas; Museth, Ken; H. P. A. Lensch and S. SeipelWe present a novel surface-tracking technique for free-surface fluid animations. Unlike the semi-implicit Particle Level Set method (PLS) our interface-tracking approach is purely implicit and hence avoids some of the well-known issues like surface noise and inflated memory footprints. Where PLS augments the interface with Lagrangian tracker-particles, we instead employ a higher resolution level set represented as a DT-Grid. The synchronization of our dual-resolution level sets is facilitated by a novel Spatially Adaptive Morphological (SAM) filter that attempts to preserve fine details while still avoiding spurious topology changes and boundary violations. We demonstrate that our approach can achieve comparative results to the PLS, but with a fraction of the memory footprint. We also show how our technique can be used to effectively enhance thin interface sheets at the cost of volume gain.Item A Survey of Real-Time Hard Shadow Mapping Methods(The Eurographics Association, 2010) Scherzer, D.; Wimmer, M.; Purgathofer, W.; Helwig Hauser and Erik ReinhardDue to its versatility, speed and robustness, shadow mapping has always been a popular algorithm for fast hard shadow generation since its introduction in 1978, first for off-line film productions and later increasingly so in real-time graphics. So it is not surprising that recent years have seen an explosion in the number of shadow map related publications. The last survey that encompassed shadow mapping approaches, but was mainly focused on soft shadow generation, dates back to 2003 [HLHS03], while the last survey for general shadow generation dates back to 1990 [WPF90]. No survey that describes all the advances made in hard shadow map generation in recent years exists. On the other hand, shadow mapping is widely used in the game industry, in production, and in many other applications, and it is the basis of many soft shadow algorithms. Due to the abundance of articles on the topic, it has become very hard for practitioners and researchers to select a suitable shadow algorithm, and therefore many applications miss out on the latest high-quality shadow generation approaches. The goal of this survey is to rectify this situation by providing a detailed overview of this field. We provide a detailed analysis of shadow mapping errors and derive from this a comprehensive classification of the existing methods. We discuss the most influential algorithms, consider their benefits and shortcomings and thereby provide the reader with the means to choose the shadow algorithm best suited to his or her needs.Item Shared Sampling for Real-Time Alpha Matting(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gastal, Eduardo S. L.; Oliveira, Manuel M.Image matting aims at extracting foreground elements from an image by means of color and opacity (alpha) estimation. While a lot of progress has been made in recent years on improving the accuracy of matting techniques, one common problem persisted: the low speed of matte computation. We present the first real-time matting technique for natural images and videos. Our technique is based on the observation that, for small neighborhoods, pixels tend to share similar attributes. Therefore, independently treating each pixel in the unknown regions of a trimap results in a lot of redundant work. We show how this computation can be significantly and safely reduced by means of a careful selection of pairs of background and foreground samples. Our technique achieves speedups of up to two orders of magnitude compared to previous ones, while producing high-quality alpha mattes. The quality of our results has been verified through an independent benchmark. The speed of our technique enables, for the first time, real-time alpha matting of videos, and has the potential to enable a new class of exciting applications.Item User-Controllable Color Transfer(The Eurographics Association and Blackwell Publishing Ltd, 2010) An, Xiaobo; Pellacini, FabioThis paper presents an image editing framework where users use reference images to indicate desired color edits. In our approach, users specify pairs of strokes to indicate corresponding regions in both the original and the reference image that should have the same color style . Within each stroke pair, a nonlinear constrained parametric transfer model is used to transfer the reference colors to the original. We estimate the model parameters by matching color distributions, under constraints that ensure no visual artifacts are present in the transfer result. To perform transfer on the whole image, we employ optimization methods to propagate the model parameters defined at each stroke location to spatially-close regions of similar appearance. This stroke-based formulation requires minimal user effort while retaining the high degree of user control necessary to allow artistic interpretations. We demonstrate our approach by performing color transfer on a number of image pairs varying in content and style, and show that our algorithm outperforms state-of-the-art color transfer methods on both user-controllability and visual qualities of the transfer results.Item Interactive Creation of Virtual Worlds Using Procedural Sketching(The Eurographics Association, 2010) Smelik, Ruben M.; Tutenel, Tim; Kraker, Klaas Jan de; Bidarra, Rafael; H. P. A. Lensch and S. SeipelProcedural modelling is an attractive alternative to cut down the costs of manual content creation for virtual worlds. We discuss our declarative modelling approach to the creation of 3D virtual worlds, which integrates a variety of procedural techniques in order to enable a non-specialist user to interactively create a complete 3D virtual world in minutes. In particular, we introduce procedural sketching, a novel paradigm which allows designers to quickly specify and see the effects of their procedural modelling operations, and describe its main features as implemented in our prototype system SketchaWorld. Two main interaction modes are described, for specifying the landscape and terrain features, respectively. Our approach automatically fits all generated terrain features with their surroundings, for example by smoothing out rough terrain for roads, or creating a bridge to cross a river. It is concluded that this approach provides designers with the productivity gain of procedural methods, while still allowing for fine user control and actively supporting iterative modelling.Item Finding Approximate Ambigrams and Making them Exact(The Eurographics Association, 2010) Loviscach, Joern; H. P. A. Lensch and S. SeipelRotational ambigrams are arrangements of letters that can also be read upside down. Existing approaches to automatically create such ambigrams employ highly artificially-looking and difficult-to-read typefaces. In contrast to that, the ambigram generator introduced here is based on a vector graphics editor that ensures perfect symmetry. A major component is an algorithm to smoothly fuse different vector shapes. As not all words lend themselves to be converted into legible ambigrams, an optional preparatory step is included. In this step, a dictionary is searched for words that are shaped almost symmetrically so that meaningful input is provided to the editing stage.Item Face Fitting using a Genetic Algorithm.(The Eurographics Association, 2010) Hunter, D.W.; Tiddeman, B. P.; Perrett, D. I.; Anders Hast and Ivan ViolaThe ability to estimate the three-dimensional structure of a human face from a single image has many useful applications, including but not limited to the fields of face recognition, modelling and actors head replacement. Although a lot of promising techniques have been developed in this area a number of significant technical hurdles exist preventing the development of a reliable method to extract three-dimensional structure without human intervention. In this poster we present work in progress on a new technique that should overcome some of the problems associated with the current state-of-the-art methods. We intend to use Genetic Algorithms to search the face space to find a match with a given input image. We hope to show that this method will avoid local-minima problems associated with traditional gradient descent techniques as well as provide a method that locates the position, pose and shape of the face without any user interaction.Item Skeleton Computation of an Image Using a Geometric Approach(The Eurographics Association, 2010) Martinez, Jonas; Vigo, Marc; Pla-Garcia, Nuria; Ayala, Dolors; H. P. A. Lensch and S. SeipelIn this work we develop two algorithms to compute the skeleton of a binary 2D image. Both algorithms follow a geometric approach and work directly with the boundary of the image which is an orthogonal polygon (OP). One of these algorithms processes the edges of the polygon while the other one uses its vertices. Compared with a thinning method, the presented algorithms show a good performance. This is a work in progress as our final goal is to extend the vertex-based algorithm method to 3D in order to compute the surface skeleton of a binary volume.Item Synthesis of Responsive Motion Using a Dynamic Model(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ye, Yuting; Liu, C. KarenSynthesizing the movements of a responsive virtual character in the event of unexpected perturbations has proven a difficult challenge. To solve this problem, we devise a fully automatic method that learns a nonlinear probabilistic model of dynamic responses from very few perturbed walking sequences. This model is able to synthesize responses and recovery motions under new perturbations different from those in the training examples. When perturbations occur, we propose a physics-based method that initiates motion transitions to the most probable response example based on the dynamic states of the character. Our algorithm can be applied to any motion sequences without the need for preprocessing such as segmentation or alignment. The results show that three perturbed motion clips can sufficiently generate a variety of realistic responses, and 14 clips can create a responsive virtual character that reacts realistically to external forces in different directions applied on different body parts at different moments in time.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 State of the Art in Procedural Noise Functions(The Eurographics Association, 2010) Lagae, A.; Lefebvre, S.; Cook, R.; DeRose, T.; Drettakis, G.; Ebert, D. S.; Lewis, J. P.; Perlin, K.; Zwicker, M.; Helwig Hauser and Erik ReinhardProcedural noise functions are widely used in Computer Graphics, from off-line rendering in movie production to interactive video games. The ability to add complex and intricate details at low memory and authoring cost is one of its main attractions. This state-of-the-art report is motivated by the inherent importance of noise in graphics, the widespread use of noise in industry, and the fact that many recent research developments justify the need for an up-to-date survey. Our goal is to provide both a valuable entry point into the field of procedural noise functions, as well as a comprehensive view of the field to the informed reader. In this report, we cover procedural noise functions in all their aspects. We outline recent advances in research on this topic, discussing and comparing recent and well established methods. We first formally define procedural noise functions based on stochastic processes and then classify and review existing procedural noise functions. We discuss how procedural noise functions are used for modeling and how they are applied on surfaces. We then introduce analysis tools and apply them to evaluate and compare the major approaches to noise generation. We finally identify several directions for future work.Item Visualizing Climate Change: the Potential of Dome Presentations as a Tool for Climate Communication(The Eurographics Association, 2010) Neset, Tina-Simone S.; Wibeck, Victoria; Uhrqvist, Ola; Johansson, Jimmy; Matthew Cooper and Kari PulliThis study presents the outline of a climate visualization programme directed to various target groups that was presented in a dome environment. The efforts of climate and visualization researchers to jointly develop presentations for immersive environments on the cause and effect of climate change as well as potential responses both in terms of national and international policy as well as individuals lifestyles are described. Further we discuss the results of an evaluation with 64 participants of dome presentations. The results point towards an initial support for the dome visualization in terms of increased engagement of the audience. Further, visual representations such as choice of colouring and volume bar charts that were expected to be problematic by the research group were considered straightforward by the audience. In this paper we discuss visual representation and climate communication, and to what extent climate visualization in a dome environment can contribute to enhance the audience s understanding of the complexity of climate change issues.Item Mesh Decomposition with Cross-Boundary Brushes(The Eurographics Association and Blackwell Publishing Ltd, 2010) Zheng, Youyi; Tai, Chiew-LanWe present a new intuitive UI, which we call cross-boundary brushes, for interactive mesh decomposition. The user roughly draws one or more strokes across a desired cut and our system automatically returns a best cut running through all the strokes. By the different natures of part components (i.e., semantic parts) and patch components (i.e., flatter surface patches) in general models, we design two corresponding brushes: part-brush and patch-brush. These two types of brushes share a common user interface, enabling easy switch between them. The part-brush executes a cut along an isoline of a harmonic field driven by the user-specified strokes. We show that the inherent smoothness of the harmonic field together with a carefully designed isoline selection scheme lead to segmentation results that are insensitive to noise, pose, tessellation and variation in user s strokes. Our patch-brush uses a novel facet-based surface metric that alleviates sensitivity to noise and fine details common in region-growing algorithms. Extensive experimental results demonstrate that our cutting tools can produce user-desired segmentations for a wide variety of models even with single strokes. We also show that our tools outperform the state-of-art interactive segmentation tools in terms of ease of use and segmentation quality.Item USER S PREFERENCE-BASED COLOR TRANSFORMATION USING INTERACTIVE GENETIC ALGORITHM(The Eurographics Association, 2010) Kang, Hang-Bong; Woo, Hye-Yoon; Anders Hast and Ivan ViolaIn this paper, we propose a new color transform method in the image based on the user s preferences. To obtain general preferences for color, we first divided the images into two categories as favourable and unfavourable groups based on the users evaluation. From the categorized groups of images, we compute color histograms to construct general templates for 8 primary colors. To reflect the user s own preference in the color perception, we adopted an interactive genetic algorithm. In the interactive genetic algorithm, each individual consists of three chromosomes for H, S, and V and the fitness value is computed from the user s input, which is then used as criteria to iterate Genetic Algorithm for learning the user s preference. Finally, a personalized individual is generated. By transforming the colors in the image with the personalized individual, a re-colorred image is generated according to the user own preference. Survey results show that re-colorred images from our proposed personalized color templates are more satisfying than the original images.