EG2009

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https://diglib.eg.org/handle/10.2312/269

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Easel: A Java Based Top-Down Approach to 3D Graphics Education
(The Eurographics Association, 2009) Rhodes, Philip J.; Yan, Baoqiang; G. Domik and R. Scateni
We describe Easel, a simple 3D graphics pipeline implementation targeted toward undergraduate Computer Graphics education. Easel is an interactive system written entirely in Java, which presents unique challenges and opportunities for teaching not only 3D Graphics, but also a well-reasoned approach to software engineering and development. Achieving a reasonable frame rate in addition to correct results requires students to think carefully about performance, ease of implementation and maintainability.
Real-time Volumetric Lighting in Participating Media
(The Eurographics Association, 2009) Toth, Balazs; Umenhoffer, Tamas; P. Alliez and M. Magnor
Simulating light scattering in participating media, such as dust, fog or smoke, can greatly improve the overall realism of the images. This volumetric effect has been well studied in the context of off-line rendering but is still challenging for interactive applications. In this paper we present a GPU-based algorithm to compute volumetric light-shafts generated by single scattering in participating media. The proposed method uses shadow maps to account for shadowing and interleaved sampling to maintain high frame rates without sacrificing image quality.
Complex Barycentric Coordinates with Applications to Planar Shape Deformation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Weber, Ofir; Ben-Chen, Mirela; Gotsman, Craig
Applet Competition as an Educational Tool in Creating Novel e-Textbook
(The Eurographics Association, 2009) Czanner, Silvester; Ferko, Andrej; Stugel, Juraj; Nunukova, Pavla; G. Domik and R. Scateni
We introduce a long-term competition-oriented project, using learning by doing (applets). The output of this project is updated every year at http://www.netgraphics.sk/. Many undergraduate students at the University of Warwick and the Comenius University compete in developing the e-Textbook, called Computer Graphics Virtual Textbook. The current version offers supplementary material for particular CG courses but it is also an independent source of information for all people interested in CG. There is currently 126 students enrolled for this competition. Every year, the number of valuable applets or applet innovations is lower than the total number of students. The three winners of 2008 round of applet competition will be announced before Christmas (and their creations will be presented at the SCCG09 conference). The best units of this project will be submitted to CGEMS.
Scalable real-time animation of rivers
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Yu, Qizhi; Neyret, Fabrice; Bruneton, Eric; Holzschuch, Nicolas
Many recent games and applications target the interactive exploration of realistic large scale worlds. These worlds consist mostly of static terrain models, as the simulation of animated fluids in these virtual worlds is computationally expensive. Adding flowing fluids, such as rivers, to these virtual worlds would greatly enhance their realism, but causes specific issues: as the user is usually observing the world at close range, small scale details such as waves and ripples are important. However, the large scale of the world makes classical methods impractical for simulating these effects. In this paper, we present an algorithm for the interactive simulation of realistic flowing fluids in large virtual worlds. Our method relies on two key contributions: the local computation of the velocity field of a steady flow given boundary conditions, and the advection of small scale details on a fluid, following the velocity field, and uniformly sampled in screen space.
Implicit Contact Handling for Deformable Objects
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Otaduy, Miguel A.; Tamstorf, Rasmus; Steinemann, Denis; Gross, Markus
We present an algorithm for robust and efficient contact handling of deformable objects. By being aware of the internal dynamics of the colliding objects, our algorithm provides smooth rolling and sliding, stable stacking, robust impact handling, and seamless coupling of heterogeneous objects, all in a unified manner. We achieve dynamicsawareness through a constrained dynamics formulation with implicit complementarity constraints, and we present two major contributions that enable an efficient solution of the constrained dynamics problem: a time stepping algorithm that robustly ensures non-penetration and progressively refines the formulation of constrained dynamics, and a new solver for large mixed linear complementarity problems, based on iterative constraint anticipation. We show the application of our algorithm in challenging scenarios such as multi-layered cloth moving at high velocities, or colliding deformable solids simulated with large time steps.
Teaching Quaternions is not Complex
(The Eurographics Association, 2009) McDonald, John; G. Domik and R. Scateni
Quaternions are used in many fields of science and computing, but teaching them remains challenging. Students can have a great deal of trouble understanding essentially what quaternions are and how they can represent rotation matrices. In particular, the similarity transform qvq-1 which actually achieves rotation, can often be baffling even after they ve seen a full derivation. This paper outlines a constructive method for teaching quaternions, which allows students to build intuition about what quaternions are, and why simple multiplication is not adequate to represent a rotation. Through a set of examples, it demonstrates exactly how quaternions relate to rotation matrices, what goes wrong when qv is naively used to rotate vectors, and how the similarity transform fixes the problem.
Noise Robust Surface Reconstruction by Combining PU and Graph-cut
(The Eurographics Association, 2009) Nagai, Yukie; Ohtake, Yutaka; Suzuki, Hiromasa; P. Alliez and M. Magnor
We present a novel method of reconstructing surfaces from 3D scattered points by combining Partition of Unity (PU) and a Graph-cut approach. PU is a local approximation technique, meaning that the surfaces obtained have high accuracy but are sensitive to noise. Graph-cut, on the other hand, is a global algorithm that is robust to noise but produces low-accuracy results because it is a discrete binary operation. Our algorithm combines these two methods to achieve robust, high accuracy surface reconstruction. First, a PU implicit function is constructed by covering a space containing a point cloud with spherical supports of linear polynomials. Graph-cut is then performed to separate the covered domain into inside and outside areas of the object to be reconstructed. Finally, we extract the zero-level of PU using the marching tetrahedra approach.
EUROGRAPHICS Tutorial on Sketch Recognition
(The Eurographics Association, 2009) Hammond, T.; Paulson, B.; Eoff, B.; K. Museth and D. Weiskopf
Sketch recognition is the automated understanding of hand-drawn diagrams. Despite the prevalence of keyboards and mice, hand-drawings still pervade in education, design, and other diagrams. This full day tutorial explains why sketch recognition is important, the underlying algorithms, how sketch recognition can be used in traditional interfaces, and the field s experiences with sketch recognition used in different domains.
Color correction for tone mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Mantiuk, R.; Mantiuk, R.; Tomaszewska, A.; Heidrich, W.
Tone mapping algorithms offer sophisticated methods for mapping a real-world luminance range to the luminance range of the output medium but they often cause changes in color appearance. In this work we conduct a series of subjective appearance matching experiments to measure the change in image colorfulness after contrast compression and enhancement. The results indicate that the relation between contrast compression and the color saturation correction that matches color appearance is non-linear and smaller color correction is required for small change of contrast. We demonstrate that the relation cannot be fully explained by color appearance models. We propose color correction formulas that can be used with existing tone mapping algorithms. We extend existing global and local tone mapping operators and show that the proposed color correction formulas can preserve original image colors after tone scale manipulation.
A Hybrid GPU Rendering Pipeline for Alias-Free Hard Shadows
(The Eurographics Association, 2009) Hertel, Stefan; Hormann, Kai; Westermann, Rüdiger; D. Ebert and J. Krüger
We present a new GPU pipeline for rendering per-pixel exact shadows that are cast by point lights and parallel lights. Our approach is hybrid in that it uses kD-tree accelerated ray-tracing to determine shadow-ray intersections, and rasterization to effectively reduce both the number of shadow rays to be traversed and the number of sub-spaces to be considered along each of these rays. To achieve this we introduce conservative shadow maps, which store a conservative estimate of the first intersection with the scene for each possible shadow ray. A novel approach to build such a map is presented, which uses rasterization to compute for every shadow-map pixel the triangles intersecting this pixel. By exploiting the rasterization capacities of recent GPUs in combination with accurate ray-triangle intersection tests, we are able to efficiently compute alias-free shadows in high-resolution and spatially extended scenes where classical shadow mapping techniques have severe difficulties.
Time-of-Flight Sensors in Computer Graphics
(The Eurographics Association, 2009) Kolb, Andreas; Barth, Erhardt; Koch, Reinhard; Larsen, Rasmus; M. Pauly and G. Greiner
A growing number of applications depend on accurate and fast 3D scene analysis. Examples are model and lightfield acquisition, collision prevention, mixed reality, and gesture recognition. The estimation of a range map by image analysis or laser scan techniques is still a time-consuming and expensive part of such systems. A lower-priced, fast and robust alternative for distance measurements are Time-of-Flight (ToF) cameras. Recently, significant improvements have been made in order to achieve low-cost and compact ToF-devices, that have the potential to revolutionize many fields of research, including Computer Graphics, Computer Vision and Man Machine Interaction (MMI). These technologies are starting to have an impact on research and commercial applications. The upcoming generation of ToF sensors, however, will be even more powerful and will have the potential to become "ubiquitous real-time geometry devices" for gaming, web-conferencing, and numerous other applications. This STAR gives an account of recent developments in ToF-technology and discusses the current state of the integration of this technology into various graphics-related applications.
Arches: a Framework for Modeling Complex Terrains
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Peytavie, A.; Galin, E.; Grosjean, J.; Merillou, S.
In this paper, we present a framework for representing complex terrains with such features as overhangs, arches and caves and including different materials such as sand and rocks. Our hybrid model combines a volumetric discrete data structure that stores the different materials and an implicit representation for sculpting and reconstructing the surface of the terrain. Complex scenes can be edited and sculpted interactively with high level tools. We also propose an original rock generation technique that enables us to automatically generate complex rocky sceneries with piles of rocks without any computationally demanding physically-based simulation.
A Cost Metric for Scene-Interior Ray Origins
(The Eurographics Association, 2009) Fabianowski, Bartosz; Fowler, Colin; Dingliana, John; P. Alliez and M. Magnor
Acceleration structures reducing the number of intersection tests are crucial for high ray tracing performance. The best acceleration structures are currently obtained using the surface area heuristic (SAH) which greedily optimizes a cost metric based on a series of heuristic assumptions about the rays. Noting that rays in many cases originate within the scene's bounding box, we assume a uniform distribution of their origins throughout the scene and derive alternative cost metrics. Our experimental results show that at a slight increase in acceleration structure build time, an improvement in ray tracing speed over the SAH is achieved for most scenes. A more accurate metric based on our assumptions yields even more reliable speed-ups at the cost of higher construction time. We conclude that making more realistic assumptions than the SAH is a promising route for better ray tracing acceleration.
Modeling the Appearance and Behavior of Urban Spaces
(The Eurographics Association, 2009) Vanegas, Carlos A.; Aliaga, Daniel G.; Wonka, Peter; Müller, Pascal; Waddell, Paul; Watson, Benjamin; M. Pauly and G. Greiner
Urban spaces consist of a complex collection of buildings, parcels, blocks and neighborhoods interconnected by streets. Accurately modeling both the appearance and the behavior of dense urban spaces is a significant challenge. The recent surge in urban data and its availability via the Internet (e.g., Google Earth/Maps, Microsoft Visual Earth) has fomented a significant amount of research in computer graphics and in a number of applications in urban planning, emergency management, and visualization. In this state-of-the-art report, we seek to provide an overview of methods spanning computer graphics and related fields involved in this goal. Our paper reports the most prominent methods in urban modeling and rendering, urban visualization, and urban simulation models. A reader will be well versed in the key problems and current solution methods.
Completion and Reconstruction with Primitive Shapes
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Schnabel, Ruwen; Degener, Patrick; Klein, Reinhard
We consider the problem of reconstruction from incomplete point-clouds. To find a closed mesh the reconstruction is guided by a set of primitive shapes which has been detected on the input point-cloud (e.g. planes, cylinders etc.). With this guidance we not only continue the surrounding structure into the holes but also synthesize plausible edges and corners from the primitives intersections. To this end we give a surface energy functional that incorporates the primitive shapes in a guiding vector field. The discretized functional can be minimized with an efficient graph-cut algorithm. A novel greedy optimization strategy is proposed to minimize the functional under the constraint that surface parts corresponding to a given primitive must be connected. From the primitive shapes our method can also reconstruct an idealized model that is suitable for use in a CAD system.
Shape Decomposition using Modal Analysis
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Huang, Qi-Xing; Wicke, Martin; Adams, Bart; Guibas, Leonidas
We introduce a novel algorithm that decomposes a deformable shape into meaningful parts requiring only a single input pose. Using modal analysis, we are able to identify parts of the shape that tend to move rigidly. We define a deformation energy on the shape, enabling modal analysis to find the typical deformations of the shape. We then find a decomposition of the shape such that the typical deformations can be well approximated with deformation fields that are rigid in each part of the decomposition. We optimize for the best decomposition, which captures how the shape deforms. A hierarchical refinement scheme makes it possible to compute more detailed decompositions for some parts of the shape.Although our algorithm does not require user intervention, it is possible to control the process by directly changing the deformation energy, or interactively refining the decomposition as necessary. Due to the construction of the energy function and the properties of modal analysis, the computed decompositions are robust to changes in pose as well as meshing, noise, and even imperfections such as small holes in the surface.
Spectral-Based Group Formation Control
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Takahashi, Shigeo; Yoshida, Kenichi; Kwon, Taesoo; Lee, Kang Hoon; Lee, Jehee; Shin, Sung Yong
Given a pair of keyframe formations for a group consisting of multiple individuals, we present a spectral-based approach to smoothly transforming a source group formation into a target formation while respecting the clusters of the involved individuals. The proposed method provides an effective means for controlling the macroscopic spatiotemporal arrangement of individuals for applications such as expressive formations in mass performances and tactical formations in team sports. Our main idea is to formulate this problem as rotation interpolation of the eigenbases for the Laplacian matrices, each of which represents how the individuals are clustered in a given keyframe formation. A stream of time-varying formations is controlled by editing the underlying adjacency relationships among individuals as well as their spatial positions at each keyframe, and interpolating the keyframe formations while producing plausible collective behaviors over a period of time. An interactive system of editing existing group behaviors in a hierarchical fashion has been implemented to provide flexible formation control of large crowds.
Video-Realistic Image-based Eye Animation System
(The Eurographics Association, 2009) Weissenfeld, Axel; Liu, Kang; Ostermann, J.; P. Alliez and M. Magnor
In this work we elaborate on a novel image-based system for creating video-realistic eye animations to arbitrary spoken output. These animations are useful to give a face to multimedia applications such as virtual operators in dialog systems. Our eye animation system consists of two parts: eye control unit and rendering engine. The designed eye control unit is based on the statistical analysis of recorded human subjects. We design a new model, which fully automatically couples eye blinks and movements with phonetic as well as prosodic information extracted from spoken language. Subjective tests showed that participants are not able to distinguish between real eye motions and our animations, which has not been achieved before.
ImaGINe-S: Imaging Guided Interventional Needle Simulation
(The Eurographics Association, 2009) Bello, Fernando; Bulpitt, Andrew; Gould, Derek A.; Holbrey, Richard; Hunt, Carrie; How, Thien; John, Nigel W.; Johnson, Sheena; Phillips, Roger; Sinha, Amrita; Vidal, Franck; Villard, Pierre-Frédéric; Woolnough, Helen; Zhang, Yan; K. Bühler and D. Bartz
We present an integrated system for training visceral needle puncture procedures. Our aim is to provide a cost effective and validated training tool that uses actual patient data to enable interventional radiology trainees to learn how to carry out image-guided needle puncture. The input data required is a computed tomography scan of the patient that is used to create the patient specific models. Force measurements have been made on real tissue and the resulting data is incorporated into the simulator. Respiration and soft tissue deformations are also carried out to further improve the fidelity of the simulator.

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