EG2010

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https://diglib.eg.org/handle/10.2312/277

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Practical quad mesh simplification
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Tarini, Marco; Pietroni, Nico; Cignoni, Paolo; Panozzo, Daniele; Puppo, Enrico
In this paper we present an innovative approach to incremental quad mesh simplification, i.e. the task of producing a low complexity quad mesh starting from a high complexity one. The process is based on a novel set of strictly local operations which preserve quad structure. We show how good tessellation quality (e.g. in terms of vertex valencies) can be achieved by pursuing uniform length and canonical proportions of edges and diagonals. The decimation process is interleaved with smoothing in tangent space. The latter strongly contributes to identify a suitable sequence of local modification operations. The method is naturally extended to manage preservation of feature lines (e.g. creases) and varying (e.g. adaptive) tessellation densities. We also present an original Triangle-to-Quad conversion algorithm that behaves well in terms of geometrical complexity and tessellation quality, which we use to obtain the initial quad mesh from a given triangle mesh.
Path Regeneration for Interactive Path Tracing
(The Eurographics Association, 2010) Novák, Jan; Havran, Vlastimil; Dachsbacher, Carsten; H. P. A. Lensch and S. Seipel
Rendering of photo-realistic images at interactive frame rates is currently an extensively researched area of computer graphics.Many of these approaches attempt to utilize the computational power of modern graphics hardware for ray tracing based methods. When using path tracing algorithms the ray paths are highly incoherent, hence we propose an efficient technique that minimizes the divergence in execution flow and ensures full utilization by intelligently regenerating the paths. We analyze the conditions under which our improvements provide the highest speedup, and demonstrate the performance of the overall system by rendering interactive previews of global illumination solutions using (bidirectional) path tracing with progressive refinement.Rendering of photo-realistic images at interactive frame rates is currently an extensively researched area of computer graphics.Many of these approaches attempt to utilize the computational power of modern graphics hardware for ray tracing based methods. When using path tracing algorithms the ray paths are highly incoherent, hence we propose an efficient technique that minimizes the divergence in execution flow and ensures full utilization by intelligently regenerating the paths. We analyze the conditions under which our improvements provide the highest speedup, and demonstrate the performance of the overall system by rendering interactive previews of global illumination solutions using (bidirectional) path tracing with progressive refinement.
Accelerated Deterministic Simulation of X-ray Attenuation Using Graphics Hardware
(The Eurographics Association, 2010) Vidal, Franck; Garnier, M.; Freud, N.; Létang, J.M.; John, N.W.; Anders Hast and Ivan Viola
In this paper, we propose a deterministic simulation of X-ray transmission imaging on graphics hardware. Only the directly transmitted photons are simulated, using the Beer-Lambert law. Our previous attempt to simulate Xray attenuation from polygon meshes utilising the GPU showed significant increase of performance, with respect to a validated software implementation, without loss of accuracy. However, the simulations were restricted to monochromatic X-rays and finite point sources. We present here an extension to our method to perform physically more realistic simulations by taking into account polychromatic X-rays and focal spots causing blur.
A Survey on Shape Correspondence
(The Eurographics Association, 2010) Kaick, O. van; Zhang, H.; Hamarneh, G.; Cohen-Or, D.; Helwig Hauser and Erik Reinhard
We present a review of the correspondence problem and its solution methods, targeting the computer graphics audience. With this goal in mind, we focus on the correspondence of geometric shapes represented by point sets, contours or triangle meshes. This survey is motivated by recent developments in the field such as those requiring the correspondence of non-rigid or time-varying surfaces and a recent trend towards semantic shape analysis, of which shape correspondence is one of the central tasks. Establishing a meaningful shape correspondence is a difficult problem since it typically relies on an understanding of the structure of the shapes in question at both a local and global level, and sometimes also the shapes functionality. However, despite its inherent complexity, shape correspondence is a recurrent problem and an essential component in numerous geometry processing applications. In this report, we discuss the different forms of the correspondence problem and review the main solution methods, aided by several classification criteria which can be used by the reader to objectively compare the methods. We finalize the report by discussing open problems and future perspectives.
Volumetric Hand Reconstructions for Non-verbal Communication in Shared Virtual Environments
(The Eurographics Association, 2010) John, Christoph; Regenbrecht, Holger; Schwanecke, Ulrich; H. P. A. Lensch and S. Seipel
Enhancing desk-based computer environments with virtual reality technology requires natural interaction support, in particular hand tracking and visualization. In shared virtual environments hand tracking does not only support interaction with the virtual environment, but also provides a channel for non-verbal communication. This paper presents a tabletop user interface and its integration into a three-dimensional teleconferencing system. Dense volume reconstructions of hands based on a probabilistic Shape from Silhouette algorithm are applied for tracking and visualization. The interface integration employs the derived probabilistic hand reconstructions to interactively generate mesh models characterized as isosurfaces of probabilistic volume data. It will be shown, that meshes resulting from probabilistic volume reconstructions thereby exhibit superior detail in comparison to mesh models generated from non-probabilistic comparative approaches which represent the current state of the art.
Image Statistics and their Applications in Computer Graphics
(The Eurographics Association, 2010) Pouli, T.; Cunningham, D. W.; Reinhard, E.; Helwig Hauser and Erik Reinhard
The statistics of natural images have attracted the attention of researchers in a variety of fields and have been used as a means to better understand the human visual system and its processes. A number of algorithms in computer graphics, vision and image processing take advantage of such statistical findings to create visually more plausible results. With this report we aim to review the state of the art in image statistics and discuss existing and potential applications within computer graphics and related areas.
Sketching Clothoid Splines Using Shortest Paths
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Baran, Ilya; Lehtinen, Jaakko; Popovic, Jovan
Clothoid splines are gaining popularity as a curve representation due to their intrinsically pleasing curvature, which varies piecewise linearly over arc length. However, constructing them from hand-drawn strokes remains difficult. Building on recent results, we describe a novel algorithm for approximating a sketched stroke with a fair (i.e., visually pleasing) clothoid spline. Fairness depends on proper segmentation of the stroke into curve primitives - lines, arcs, and clothoids. Our main idea is to cast the segmentation as a shortest path problem on a carefully constructed weighted graph. The nodes in our graph correspond to a vastly overcomplete set of curve primitives that are fit to every subsegment of the sketch, and edges correspond to transitions of a specified degree of continuity between curve primitives. The shortest path in the graph corresponds to a desirable segmentation of the input curve. Once the segmentation is found, the primitives are fit to the curve using non-linear constrained optimization. We demonstrate that the curves produced by our method have good curvature profiles, while staying close to the user sketch.
Visual Analysis of Large Graphs
(The Eurographics Association, 2010) Landesberger, T. von; Kuijper, A.; Schreck, T.; Kohlhammer, J.; Wijk, J. J. van; Fekete, J.-D.; Fellner, Dieter W.; Helwig Hauser and Erik Reinhard
The analysis of large graphs plays a prominent role in various fields of research and is relevant in many important application areas. Effective visual analysis of graphs requires appropriate visual presentations in combination with respective user interaction facilities and algorithmic graph analysis methods. How to design appropriate graph analysis systems depends on many factors, including the type of graph describing the data, the analytical task at hand, and the applicability of graph analysis methods. The most recent surveys of graph visualization and navigation techniques were presented by Herman et al. [HMM00] and Diaz [DPS02]. The first work surveyed the main techniques for visualization of hierarchies and graphs in general that had been introduced until 2000. The second work concentrated on graph layouts introduced until 2002. Recently, new techniques have been developed covering a broader range of graph types, such as time-varying graphs. Also, in accordance with ever growing amounts of graph-structured data becoming available, the inclusion of algorithmic graph analysis and interaction techniques becomes increasingly important. In this State-of-the-Art Report, we survey available techniques for the visual analysis of large graphs. Our review firstly considers graph visualization techniques according to the type of graphs supported. The visualization techniques form the basis for the presentation of interaction approaches suitable for visual graph exploration. As an important component of visual graph analysis, we discuss various graph algorithmic aspects useful for the different stages of the visual graph analysis process.
Scalable Height Field Self-Shadowing
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Timonen, Ville; Westerholm, Jan
We present a new method suitable for general purpose graphics processing units to render self-shadows on dynamic height fields under dynamic light environments in real-time. Visibility for each point in the height field is determined as the exact horizon for a set of azimuthal directions in time linear in height field size and the number of directions. The surface is shaded using the horizon information and a high-resolution light environment extracted on-line from a high dynamic range cube map, allowing for detailed extended shadows. The desired accuracy for any geometric content and lighting complexity can be matched by choosing a suitable number of azimuthal directions. Our method is able to represent arbitrary features of both high- and low-frequency, unifying hard and soft shadowing. We achieve 23 fps on 1024x1024 height fields with 64 azimuthal directions under a 256x64 environment lighting on an Nvidia GTX 280 GPU.
Ray Tracing using Hierarchies of Slab Cut Balls
(The Eurographics Association, 2010) Källberg, Linus; Larsson, Thomas; H. P. A. Lensch and S. Seipel
In this paper, bounding volume trees of slab cut balls are evaluated and compared with other types of trees for ray tracing. A novel tree construction algorithm is proposed, which utilizes a relative orientation heuristic between parent and child nodes. Also, a fast intersection test between a ray and a slab cut ball is presented. Experimental comparisons to other commonly used enclosing shapes reveal that the slab cut ball is attractive. In particular, the slab cut ball outperforms the sphere in all tested scenes with speed-up factors between 1 and 4.
Towards an Academic Praxis for Domed Virtual Environments
(The Eurographics Association, 2010) Carss, Peter; Matthew Cooper and Kari Pulli
This paper sets out the current state of activities for the domed virtual environment located within the University of Plymouth, UK. Some of these activities have arisen through reactions to demands on the dome. Some, particularly those concerning students education, have arisen by design. The paper describes the theoretical frameworks, curricula, methodologies and tools that have emerged, and suggests that these are first steps towards what might be termed a praxis of domed virtual environments.
Adapting Precomputed Radiance Transfer to Real-time Spectral Rendering
(The Eurographics Association, 2010) Schwenk, Karsten; Franke, Tobias; Drevensek, Timm; Kuijper, Arjan; Bockholt, Ulrich; Fellner, Dieter W.; H. P. A. Lensch and S. Seipel
Spectral rendering takes the full visible spectrum into account when calculating light-surface interaction and can overcome the well-known deficiencies of rendering with tristimulus color models. We present a variant of the precomputed radiance transfer algorithm that is tailored towards real-time spectral rendering on modern graphics hardware. Our method renders diffuse, self-shadowing objects with spatially varying spectral reflectance properties under distant, dynamic, full-spectral illumination. To achieve real-time frame rates and practical memory requirements we split the light transfer function into an achromatic part that varies per vertex and a wavelengthdependent part that represents a spectral albedo texture map. As an additional optimization, we project reflectance and illuminant spectra into an orthonormal basis. One area of application for our research is virtual design applications that require relighting objects with high color fidelity at interactive frame rates.Spectral rendering takes the full visible spectrum into account when calculating light-surface interaction and can overcome the well-known deficiencies of rendering with tristimulus color models. We present a variant of the precomputed radiance transfer algorithm that is tailored towards real-time spectral rendering on modern graphics hardware. Our method renders diffuse, self-shadowing objects with spatially varying spectral reflectance properties under distant, dynamic, full-spectral illumination. To achieve real-time frame rates and practical memory requirements we split the light transfer function into an achromatic part that varies per vertex and a wavelengthdependent part that represents a spectral albedo texture map. As an additional optimization, we project reflectance and illuminant spectra into an orthonormal basis. One area of application for our research is virtual design applications that require relighting objects with high color fidelity at interactive frame rates.
SoundRiver: Semantically-Rich Sound Illustration
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Jaenicke, H.; Borgo, R.; Mason, J. S. D.; Chen, M.
Sound is an integral part of most movies and videos. In many situations, viewers of a video are unable to hear the sound track, for example, when watching it in a fast forward mode, viewing it by hearing-impaired viewers or when the plot is given as a storyboard. In this paper, we present an automated visualization solution to such problems. The system first detects the common components (such as music, speech, rain, explosions, and so on) from a sound track, then maps them to a collection of programmable visual metaphors, and generates a composite visualization. This form of sound visualization, which is referred to as SoundRiver, can be also used to augment various forms of video abstraction and annotated key frames and to enhance graphical user interfaces for video handling software. The SoundRiver conveys more semantic information to the viewer than traditional graphical representations of sound illustration, such as phonoautographs, spectrograms or artistic audiovisual animations.
Designing Multi-projector VR Systems: From Bits to Bolts
(The Eurographics Association, 2010) Soares, Luciano Pereira; Jorge, Joaquim A.; Dias, José Miguel Salles; Raposo, Alberto; Araújo, Bruno R. de; U. Assarsson and D. Weiskopf
This tutorial will present how to design, construct and manage immersive multi-projection environments, covering everything from projection technologies to computer hardware and software integration. Topics as tracking, multimodal interactions and audio are going to be explored. At the end, we are going to present important design decisions from real cases. <br> The objective of this tutorial is to give an introduction to the issues to consider when planning the installation of a multi-projection environment for researchers and professionals in the computer graphics and virtual reality field. No previous knowledge is necessary in the audience for the tutorial, except for basic knowledge of computer graphics and virtual reality.
A Film Balloon Design System Integrated with Shell Element Simulation
(The Eurographics Association, 2010) Furuta, Yohsuke; Umetani, Nobuyuki; Mitani, Jun; Igarashi, Takeo; Fukui, Yukio; H. P. A. Lensch and S. Seipel
CAD systems that have user-friendly interfaces for assisting ordinary people to design objects is becoming common. Most of these systems combine a sketch interface with physical simulation. In this paper, we propose a system for designing balloons made of non-stretchy material such as aluminum foil, plastic film and paper. We implemented the system by using a finite element method that is based on discrete Kirchhoff triangle (DKT) shell elements and a sketch interface that enables users to easily design the realistic shape of an inflated balloon. The 2D pattern for the balloon design is generated automatically by our system. We evaluated our system by a user study with six elementary school children and their parents. These users designed target objects and responded to a questionnaire.
BetweenIT: An Interactive Tool for Tight Inbetweening
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Whited, Brian; Noris, Gioacchino; Simmons, Maryann; Sumner, Robert W.; Gross, Markus; Rossignac, Jarek
The generation of inbetween frames that interpolate a given set of key frames is a major component in the production of a 2D feature animation. Our objective is to considerably reduce the cost of the inbetweening phase by offering an intuitive and effective interactive environment that automates inbetweening when possible while allowing the artist to guide, complement, or override the results. Tight inbetweens, which interpolate similar key frames, are particularly time-consuming and tedious to draw. Therefore, we focus on automating these high-precision and expensive portions of the process. We have designed a set of user-guided semi-automatic techniques that fit well with current practice and minimize the number of required artist-gestures. We present a novel technique for stroke interpolation from only two keys which combines a stroke motion constructed from logarithmic spiral vertex trajectories with a stroke deformation based on curvature averaging and twisting warps. We discuss our system in the context of a feature animation production environment and evaluate our approach with real production data.
Intelligent Games for Education - An Intention Monitoring Approach based on Dynamic Bayesian Network
(The Eurographics Association, 2010) Cheng, Irene; Chen, Feng; Rodrigues, Saul Daniel; Pañella, Oscar Garcia; Vicent, Lluis; Basu, Anup; L. Kjelldahl and G. Baronoski
Computer games have become one of the preferred choices for entertainment in our society primarily because they are interactive, have appealing multimedia content, and provide an immersive and rewarding environment for players. These qualities constitute an essential psychophysical factor that inspires learning abilities and new knowledge. Despite all these promising elements, studies have shown that current educational games are not as effective as they could be. A lack of adaptive tutoring and feedback tools, lack of proper knowledge assessment, and weakly designed gameplay are the major factors for their inefficiency.We address these problems by proposing an Intelligent Tutoring System (ITS) for computer games. An important contribution of this ITS is its capability to track player intentions and award partial marks, which provides more accurate assessment than simply giving full mark to the correct result and none to an incorrect answer. Two strategies adopted in this system are Bayesian Networks based student modeling and individualized tutoring. The system can incorporate one or more games and can address one or more educational topic. The information collected from student interaction with computer games is used to update a student module that reports a student s current level of knowledge, making adaptive tutoring and assessment with computer games more effective. In order to provide an engaging and interactive environment, each game in the system has a local student module constructed based on a Dynamic Bayesian Network. We describe the design and evaluation of our ITS using a prototype implementation with several game examples. Positive evaluation results support the feasibility of the proposed system.
Improved Variational Guiding of Smoke Animations
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Nielsen, Michael B.; Christensen, Brian B.
Smoke animations are hard to art-direct because simple changes in parameters such as simulation resolution often lead to unpredictable changes in the final result. Previous work has addressed this problem with a guiding approach which couples low-resolution simulations - that exhibit the desired flow and behaviour - to the final, high-resolution simulation. This is done in such a way that the desired low frequency features are to some extent preserved in the high-resolution simulation. However, the steady (i.e. constant) guiding used often leads to a lack of sufficiently high detail, and employing time-dependent guiding is expensive because the matrix of the resulting set of equations needs to be recomputed at every iteration. We propose an improved mathematical model for Eulerian-based simulations which is better suited for dynamic, time-dependent guiding of smoke animations through a novel variational coupling of the low- and high-resolution simulations. Our model results in a matrix that does not require re-computation when the guiding changes over time, and hence we can employ time-dependent guiding more efficiently both in terms of storage and computational requirements. We demonstrate that time-dependent guiding allows for more high frequency detail to develop without losing correspondence to the low resolution simulation. Furthermore, we explore various artistic effects made possible by time-dependent guiding.
Advanced Material Appearance Models
(The Eurographics Association, 2010) Dorsey, Julie; Rushmeier, Holly; U. Assarsson and D. Weiskopf
This tutorial will cover the foundational elements of advanced material appearance models. For many years appearance models in computer graphics focused on general models for reflectance functions coupled with texture maps. However, even very common materials such as hair, skin, fabric, and rusting metal require more sophisticated models to appear realistic. In the tutorial we will begin by briefly reviewing basic reflectance models and the use of texture maps. We will then describe some common themes in advanced material models that include combining the effects of layers, groups of particles and or fibers. We will survey the detailed models necessary needed to model materials such as (but not limited to) skin (including pigmentation, pores, subsurface scattering), plants (including internal structure affecting scattering and characteristic shapes) and paints (including color flop and sparkle effects in automotive paints). In the next section of the tutorial we will treat the modeling of complex appearance due to aging and weathering processes. A general taxonomy of these effects will be presented, as well as methods to simulate and to capture these effects. The tutorial will close with a look at current trends in material modeling research. Important new trends include new interfaces for modeling materials, insights into material perception, and the availability of code and data for material models.
Real-Time Smoke Rendering and Light Interaction
(The Eurographics Association, 2010) Bass, Christopher J.; Anderson, Eike Falk; Anders Hast and Ivan Viola
In computer graphics, smoke can be represented by using particle systems. Adding shadows to particle systems can go a long way to improve visuals and realism. Our work is concerned with external shadows cast onto a particle system by an occluding object, for which shadow mapping is combined with the particle system in an implementation that uses the Graphics Processing Unit (GPU).

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