30-Issue 1

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https://diglib.eg.org/handle/10.2312/161

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    Motion Blur Rendering: State of the Art
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Navarro, Fernando; Serón, Francisco J.; Gutierrez, Diego; Eduard Groeller and Holly Rushmeier
    Motion blur is a fundamental cue in the perception of objects in motion. This phenomenon manifests as a visible trail along the trajectory of the object and is the result of the combination of relative motion and light integration taking place in film and electronic cameras. In this work, we analyse the mechanisms that produce motion blur in recording devices and the methods that can simulate it in computer generated images. Light integration over time is one of the most expensive processes to simulate in high-quality renders, as such, we make an in-depth review of the existing algorithms and we categorize them in the context of a formal model that highlights their differences, strengths and limitations. We finalize this report proposing a number of alternative classifications that will help the reader identify the best technique for a particular scenario.
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    Review: Kd-tree Traversal Algorithms for Ray Tracing
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Hapala, M.; Havran, V.; Eduard Groeller and Holly Rushmeier
    In this paper we review the traversal algorithms for kd-trees for ray tracing. Ordinary traversal algorithms such as sequential, recursive, and those with neighbour-links have different limitations, which led to several new developments within the last decade. We describe algorithms exploiting ray coherence and algorithms designed with specific hardware architecture limitations such as memory latency and consumption in mind. We also discuss the robustness of traversal algorithms as one issue that has been neglected in previous research.
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    A Survey of Ocean Simulation and Rendering Techniques in Computer Graphics
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Darles, E.; Crespin, B.; Ghazanfarpour, D.; Gonzato, J.C.; Eduard Groeller and Holly Rushmeier
    This paper presents a survey of ocean simulation and rendering methods in computer graphics. To model and animate the ocean’s surface, these methods mainly rely on two main approaches: on the one hand, those which approximate ocean dynamics with parametric, spectral or hybrid models and use empirical laws from oceanographic research. We will see that this type of methods essentially allows the simulation of ocean scenes in the deep water domain, without breaking waves. On the other hand, physically-based methods use Navier–Stokes equations to represent breaking waves and more generally ocean surface near the shore. We also describe ocean rendering methods in computer graphics, with a special interest in the simulation of phenomena such as foam and spray, and light’s interaction with the ocean surface.
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    A Survey of Real-Time Hard Shadow Mapping Methods
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Scherzer, Daniel; Wimmer, Michael; Purgathofer, Werner; Eduard Groeller and Holly Rushmeier
    Because of 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 offline 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. Because of 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 show a detailed analysis of shadow mapping errors and derive a comprehensive classification of the existing methods. We discuss the most influential algorithms, consider their benefits and shortcomings and thereby provide the readers with the means to choose the shadow algorithm best suited to their needs.
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    11th International Symposium on Virtual Reality, Archaology and Cultural Heritge: 8th Eurographics Workshop on Graphics and Cultural Heritage
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Artusi, Alessandro; Joly, Morwena; Lucet, Geneviève; Ribes, Alejandro; Pitzalis, Denis; Eduard Groeller and Holly Rushmeier
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    Allometric Scaling for Character Design
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) McGraw, T.; Kawai, T.; Richards, J.; Eduard Groeller and Holly Rushmeier
    Geometric scaling transformations do not respect the biological processes which govern the size and shape of living creatures. In this paper, we describe an approach to scaling which can be related to biological function. We use known biological laws of allometry which are expressed as power laws to control the mesh deformation in the frequency domain. This approach is motivated by the relation between fractal biological systems and their underlying power-law spectra. We demonstrate our approach to biology-aware character scaling on triangle meshes representing quadrupedal mammals.
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    Taylor Prediction for Mesh Geometry Compression
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Courbet, Clément; Hudelot, Céline; Eduard Groeller and Holly Rushmeier
    In this paper, we introduce a new formalism for mesh geometry prediction. We derive a class of smooth linear predictors from a simple approach based on the Taylor expansion of the mesh geometry function. We use this method as a generic way to compute weights for various linear predictors used for mesh compression and compare them with those of existing methods. We show that our scheme is actually equivalent to the Modified Butterfly subdivision scheme used for wavelet mesh compression. We also build new efficient predictors that can be used for connectivity-driven compression in place of other schemes like Average/Dual Parallelogram Prediction and High Degree Polygon Prediction. The new predictors use the same neighbourhood, but do not make any assumption on mesh anisotropy. In the case of Average Parallelogram Prediction, our new weights improve compression rates from 3% to 18% on our test meshes. For Dual Parallelogram Prediction, our weights are equivalent to those of the previous Freelence approach, that outperforms traditional schemes by 16% on average. Our method effectively shows that these weights are optimal for the class of smooth meshes. Modifying existing schemes to make use of our method is free because only the prediction weights have to be modified in the code.
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    Eurographics 2010 Workshop on 3D Object Retrieval (EG 3DOR’10) in cooperation with ACM SIGGRAPH
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Daoudi, Mohamed; Schreck, Tobias; Eduard Groeller and Holly Rushmeier
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    Editorial
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Groeller, Eduard; Rushmeier, Holly; Eduard Groeller and Holly Rushmeier
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    Experimental Feedback on Prog and Play: A Serious Game for Programming Practice
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Muratet, M.; Torguet, P.; Viallet, F.; Jessel, J.P.; Eduard Groeller and Holly Rushmeier
    This paper presents an experimental feedback on a serious game dedicated to strengthening programming skills. This serious game, called Prog&Play, is built on an open source real-time strategy game. Its goal is to be compatible with different students, teachers and institutions. We based its evaluation on an iterative process that allows to implement the game and carry out experimentations in several contexts. Through this assessment, we define a framework which has been tested by third parties and we analyse both positive and negative points to improve the project. Evaluation is indeed beneficial and enables you to establish communication about the implemented practices.
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    Eurographics Workshops VCBM 2008 and 2010
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Wiebel, Alexander; Botha, Charl; Preim, Bernhard; Eduard Groeller and Holly Rushmeier
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    Compact Models
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Coll, Narcís; Paradinas, Teresa; Eduard Groeller and Holly Rushmeier
    Development of approximation techniques for highly detailed surfaces is one of the challenges faced today. We introduce a new mesh structure that allows dense triangular meshes of arbitrary topology to be approximated. The structure is constructed from the information gathered during a simplification process. Each vertex of the simplified model collects a neighbourhood of input vertices. Then, each neighbourhood is fitted by a set of local surfaces taking into account the sharp features detected. The simplified model plus the parameters of these local surfaces, conveniently stored in a file, is what we call Compact Model (CM). The input model can be approximated from its CM by refining each triangle of the simplified model. The main feature of our approach is that each triangle is refined by blending the local surfaces at its vertices, which can be done independently of the others. Consequently, adaptive reconstructions are possible, local shape deformations can be incorporated and the whole approximation process can be completely parallelized.
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    Using VisTrails and Provenance for Teaching Scientific Visualization
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Silva, Cláudio T.; Anderson, Erik; Santos, Emanuele; Freire, Juliana; Eduard Groeller and Holly Rushmeier
    Over 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.
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    Bertin was Right: An Empirical Evaluation of Indexing to Compare Multivariate Time-Series Data Using Line Plots
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Aigner, W.; Kainz, C.; Ma, R.; Miksch, S.; Eduard Groeller and Holly Rushmeier
    Line plots are very well suited for visually representing time-series. However, several difficulties arise when multivariate heterogeneous time-series data is displayed and compared visually. Especially, if the developments and trends of time-series of different units or value ranges need to be compared, a straightforward overlay could be visually misleading. To mitigate this, visualization pioneer Jacques Bertin presented a method called indexing that transforms data into comparable units for visual representation. In this paper, we want to provide empirical evidence for this method and present a comparative study of the three visual comparison methods linear scale with juxtaposition, log scale with superimposition and indexing. Although for task completion times, indexing only shows slight advantages, the results support the assumption that the indexing method enables the user to perform comparison tasks with a significantly lower error rate. Furthermore, a post-test questionnaire showed that the majority of the participants favour the indexing method over the two other comparison methods.
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    Hermite Radial Basis Functions Implicits
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Macedo, I.; Gois, J. P.; Velho, L.; Eduard Groeller and Holly Rushmeier
    The Hermite radial basis functions (HRBF) implicits reconstruct an implicit function which interpolates or approximates scattered multivariate Hermite data (i.e. unstructured points and their corresponding normals). Experiments suggest that HRBF implicits allow the reconstruction of surfaces rich in details and behave better than previous related methods under coarse and/or non-uniform samplings, even in the presence of close sheets. HRBF implicits theory unifies a recently introduced class of surface reconstruction methods based on radial basis functions (RBF), which incorporate normals directly in their problem formulation. Such class has the advantage of not depending on manufactured offset-points to ensure existence of a non-trivial implicit surface RBF interpolant. In fact, we show that HRBF implicits constitute a particular case of Hermite–Birkhoff interpolation with radial basis functions, whose main results we present here. This framework not only allows us to show connections between the present method and others but also enable us to enhance the flexibility of our method by ensuring well-posedness of an interesting combined interpolation/regularization approach.
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    A Parallel SPH Implementation on Multi-Core CPUs
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Ihmsen, Markus; Akinci, Nadir; Becker, Markus; Teschner, Matthias; Eduard Groeller and Holly Rushmeier
    This paper presents a parallel framework for simulating fluids with the Smoothed Particle Hydrodynamics (SPH) method. For low computational costs per simulation step, efficient parallel neighbourhood queries are proposed and compared. To further minimize the computing time for entire simulation sequences, strategies for maximizing the time step and the respective consequences for parallel implementations are investigated. The presented experiments illustrate that the parallel framework can efficiently compute large numbers of time steps for large scenarios. In the context of neighbourhood queries, the paper presents optimizations for two efficient instances of uniform grids, that is, spatial hashing and index sort. For implementations on parallel architectures with shared memory, the paper discusses techniques with improved cache-hit rate and reduced memory transfer. The performance of the parallel implementations of both optimized data structures is compared. The proposed solutions focus on systems with multiple CPUs. Benefits and challenges of potential GPU implementations are only briefly discussed.
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    CheckViz: Sanity Check and Topological Clues for Linear and Non-Linear Mappings
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Lespinats, Sylvain; Aupetit, Michaël; Eduard Groeller and Holly Rushmeier
    Multidimensional scaling is a must-have tool for visual data miners, projecting multidimensional data onto a two-dimensional plane. However, what we see is not necessarily what we think about. In many cases, end-users do not take care of scaling the projection space with respect to the multidimensional space. Anyway, when using non-linear mappings, scaling is not even possible. Yet, without scaling geometrical structures which might appear do not make more sense than considering a random map. Without scaling, we shall not make inference from the display back to the multidimensional space. No clusters, no trends, no outliers, there is nothing to infer without first quantifying the mapping quality. Several methods to qualify mappings have been devised. Here, we propose CheckViz, a new method belonging to the framework of Verity Visualization. We define a two-dimensional perceptually uniform colour coding which allows visualizing tears and false neighbourhoods, the two elementary and complementary types of geometrical mapping distortions, straight onto the map at the location where they occur. As examples shall demonstrate, this visualization method is essential to help users make sense out of the mappings and to prevent them from over interpretations. It could be applied to check other mappings as well.
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    Free Path Sampling in High Resolution Inhomogeneous Participating Media
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Szirmay-Kalos, László; Tóth, Balázs; Magdics, Milán; Eduard Groeller and Holly Rushmeier
    This paper presents efficient algorithms for free path sampling in heterogeneous participating media defined either by high-resolution voxel arrays or generated procedurally. The method is based on the concept of mixing ‘virtual’ material or particles to the medium, augmenting the extinction coefficient to a function for which the free path can be sampled in a straightforward way. The virtual material is selected such that it modifies the volume density but does not alter the radiance. We define the total extinction coefficient of the real and virtual particles by a low-resolution grid of super-voxels that are much larger than the real voxels defining the medium. The computational complexity of the proposed method depends just on the resolution of the super-voxel grid and does not grow with the resolution above the scale of super-voxels. The method is particularly efficient to render large, low-density, heterogeneous volumes, which should otherwise be defined by enormously high resolution voxel grids and where the average free path length would cross many voxels.
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    On Neighbourhood Matching for Texture-by-Numbers
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Sivaks, Eliyahu; Lischinski, Dani; Eduard Groeller and Holly Rushmeier
    Texture-by-Numbers is an attractive texture synthesis framework, because it is able to cope with non-homogeneous texture exemplars, and provides the user with intuitive creative control over the outcome of the synthesis process. Like many other exemplar-based texture synthesis methods, its basic underlying mechanism is neighbourhood matching. In this paper we review a number of commonly used neighbourhood matching acceleration techniques, compare and analyse their performance in the specific context of Texture-by-Numbers (as opposed to ordinary unconstrained texture synthesis). Our study indicates that the standard approaches are not optimally suited for the Texture-by-Numbers framework, often producing visually inferior results compared to searching for the exact L2nearest neighbour. We then show that performing Texture-by-Number using the Texture Optimization framework in conjunction with an efficient FFT-based search is able to produce good results in reasonable running times and with a minimal memory overhead.
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    Illustrative Visualization of a Vortex Breakdown Bubble
    (The Eurographics Association and Blackwell Publishing Ltd., 2011) Hummel, Mathias; Garth, Christoph; Hamann, Bernd; Hagan, Hans; Joy, Kenneth I.; Eduard Groeller and Holly Rushmeier