EG2008

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Multiperspective Modeling, Rendering, and Imaging
(The Eurographics Association, 2008) Yu, Jingyi; McMillan, Leonard; Sturm, Peter; Theoharis Theoharis and Philip Dutre
A perspective image represents the spatial relationships of objects in a scene as they appear from a single viewpoint. In contrast, a multiperspective image combines what is seen from several viewpoints into a single image. Despite their incongruity of view, effective multiperspective images are able to preserve spatial coherence and can depict, within a single context, details of a scene that are simultaneously inaccessible from a single view, yet easily interpretable by a viewer. In computer vision, multiperspective images have been used for analyzing structure revealed via motion and generating panoramic images with a wide field-of-view using mirrors. In this STAR, we provide a practical guide on topics in multiperspective modeling and rendering methods and multiperspective imaging systems. We start with a brief review of multiperspective image techniques frequently employed by artists such as the visual paradoxes of Escher, the Cubism of Picasso and Braque, and multiperspective panoramas in cel animations. We then characterize existing multiperspective camera models, with an emphasis on their underlying geometry and image properties. We demonstrate how to use these camera models for creating specific multiperspective rendering effects. Furthermore, we show that many of these cameras satisfy the multiperspective stereo constraints and we demonstrate several multiperspective imaging systems for extracting 3D geometry for computer vision. The participants learn about topics in multiperspective modeling and rendering for generating compelling pictures for computer graphics and in multiperspective imaging for extracting 3D geometry for computer vision. We hope to provide enough fundamentals to satisfy the technical specialist without intimidating curious digital artists interested in multiperspective images. The intended audience includes digital artists, photographers, and computer graphics and computer vision researchers using or building multiperspective cameras. They will learn about multiperspective modeling and rendering, along with many real world multiperspective imaging systems.
Photo-realistic Rendering of Metallic Car Paint from Image-Based Measurements
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Rump, Martin; Mueller, Gero; Sarlette, Ralf; Koch, Dirk; Klein, Reinhard
State-of-the-art car paint shows not only interesting and subtle angular dependency but also significant spatial variation. Especially in sunlight these variations remain visible even for distances up to a few meters and give the coating a strong impression of depth which cannot be reproduced by a single BRDF model and the kind of procedural noise textures typically used. Instead of explicitly modeling the responsible effect particles we propose to use image-based reflectance measurements of real paint samples and represent their spatial varying part by Bidirectional Texture Functions (BTF). We use classical BRDF models like Cook-Torrance to represent the reflection behavior of the base paint and the highly specular finish and demonstrate how the parameters of these models can be derived from the BTF measurements. For rendering, the image-based spatially varying part is compressed and efficiently synthesized. This paper introduces the first hybrid analytical and image-based representation for car paint and enables the photo-realistic rendering of all significant effects of highly complex coatings.
Efficient Soft Tissue Modelling Using Charged Particle Control Points
(The Eurographics Association, 2008) Buckley, Oliver; John, Nigel W.; Katerina Mania and Eric Reinhard
As the performance levels of personal computers increases so does the desire for more realistic and immersive software and simulation. An area where this is particularly the case is that of medical training simulation, where there is an increasing demand for high fidelity virtual environments. However, realistically modeling of soft tissue deformation still poses a considerable challenge especially when haptic feedback is required. This paper presents a new approach to soft tissue deformation using a novel Charged Particle method to control the haptic rendering while also adding a further level of realism by incorporating independent high resolution visualization to the simulation.
GPU-based Fast Ray Casting for a Large Number of Metaballs
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Kanamori, Yoshihiro; Szego, Zoltan; Nishita, Tomoyuki
Metaballs are implicit surfaces widely used to model curved objects, represented by the isosurface of a density field defined by a set of points. Recently, the results of particle-based simulations have been often visualized using a large number of metaballs, however, such visualizations have high rendering costs. In this paper we propose a fast technique for rendering metaballs on the GPU. Instead of using polygonization, the isosurface is directly evaluated in a per-pixel manner. For such evaluation, all metaballs contributing to the isosurface need to be extracted along each viewing ray, on the limited memory of GPUs. We handle this by keeping a list of metaballs contributing to the isosurface and efficiently update it. Our method neither requires expensive precomputation nor acceleration data structures often used in existing ray tracing techniques. With several optimizations, we can display a large number of moving metaballs quickly.
Real-Time Translucent Rendering Using GPU-based Texture Space Importance Sampling
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Chang, Chih-Wen; Lin, Wen-Chieh; Ho, Tan-Chi; Huang, Tsung-Shian; Chuang, Jung-Hong
We present a novel approach for real-time rendering of translucent surfaces. The computation of subsurface scattering is performed by first converting the integration over the 3D model surface into an integration over a 2D texture space and then applying importance sampling based on the irradiance stored in the texture. Such a conversion leads to a feasible GPU implementation and makes real-time frame rate possible. Our implementation shows that plausible images can be rendered in real time for complex translucent models with dynamic light and material properties. For objects with more apparent local effect, our approach generally requires more samples that may downgrade the frame rate. To deal with this case, we decompose the integration into two parts, one for local effect and the other for global effect, which are evaluated by the combination of available methods [DS03, MKB* 03a] and our texture space importance sampling, respectively. Such a hybrid scheme is able to steadily render the translucent effect in real time with a fixed amount of samples.
Graphics based Computer Adaptive Testing and Beyond
(The Eurographics Association, 2008) Cheng, Irene; Basu, Anup; Steve Cunningham and Lars Kjelldahl
Instead of computer games, animations, cartoons, and videos being used only for entertainment by kids, there is now an interest in using graphics for 'innovative testing'. Rather than traditional pen-and-paper tests, audio, video and graphics are being conceived as alternative means for more effective testing in the future. In this paper we review some examples of graphics item types for testing. As well, we outline how games can be used to interactively test concepts; discuss designing chemistry item types with interactive graphics; suggest approaches for automatically adjusting difficulty level in interactive graphics based questions; and propose strategies for giving partial marks for incorrect answers. We study how to test different cognitive skills, such as music, using multimedia interfaces; and also evaluate the effectiveness of our model. A method for estimating difficulty level of a mathematical item type using Item Response Theory (IRT) is discussed. Evaluation of the graphics item types through extensive testing on some students is also described. All of the graphics implementations shown in this report are developed by members of our research group.
Adaptive Remeshing of Non-Manifold Surfaces
(The Eurographics Association, 2008) Zilske, Michael; Lamecker, Hans; Zachow, Stefan; Katerina Mania and Eric Reinhard
We present a unified approach for consistent remeshing of arbitrary non-manifold triangle meshes with additional user-defined feature lines, which together form a feature skeleton. Our method is based on local operations only and produces meshes of high regularity and triangle quality while preserving the geometry as well as topology of the feature skeleton and the input mesh.
Quadruped Animation
(The Eurographics Association, 2008) Skrba, Ljiljana; Reveret, Lionel; Hetroy, Franck; Cani, Marie-Paule; O'Sullivan, Carol; Theoharis Theoharis and Philip Dutre
Films like Shrek, Madagascar, The Chronicles of Narnia and Charlotte s web all have something in common: realistic quadruped animations. While the animation of animals has been popular for a long time, the technical challenges associated with creating highly realistic, computer generated creatures have been receiving increasing attention recently. The entertainment, education and medical industries have increased the demand for simulation of realistic animals in the computer graphics area. In order to achieve this, several challenges need to be overcome: gathering and processing data that embodies the natural motion of an animal which is made more difficult by the fact that most animals cannot be easily motion-captured; build accurate kinematic models for animals, in particular with adapted animation skeletons; and develop either kinematic or physically-based animation methods, either embedding some a priori knowledge about the way that quadrupeds locomote and/or building on some example of real motion. In this state of the art report, we present an overview of the common techniques used to date for realistic quadruped animation. This includes an outline of the various ways that realistic quadruped motion can be achieved, through video-based acquisition, physics based models, inverse kinematics, or some combination of the above. The research presented represents a cross fertilisation of vision, graphics and interaction methods.
Knitty: 3D Modeling of Knitted Animals with a Production Assistant Interface
(The Eurographics Association, 2008) Igarashi, Yuki; Igarashi, Takeo; Suzuki, Hiromasa; Katerina Mania and Eric Reinhard
Knitty is an interactive design system for creating knitted animals. The user designs a 3D surface model using a sketching interface. The system automatically generates a knitting pattern and then visualizes the shape of the resulting 3D animal model by applying a simple physics simulation. The user can see the resulting shape before beginning the actual knitting. The system also provides a production assistant interface for novices. The user can easily understand how to knit each stitch and what to do in each step. In a workshop for novices, we observed that even children can design their own knitted animals using our system.
Post Facto Registration Tools for Urban Modelling
(The Eurographics Association, 2008) Morvan, Yann; Hinks, Tommy; Carr, Hamish; Laefer, Debra F.; O'Sullivan, Carol; Morrish, W. Sean; Katerina Mania and Eric Reinhard
Urban modelling applications require high-precision geometric models both for graphical rendering and for engineering purposes. While geometric models, photographic images and laser-scanned point clouds are ideally co-registered to national coordinate grids at the time of acquisition, the quantity and diversity of data sources means that registration must often be performed post facto. Moreover, the sheer size of urban point clouds prevents automated conversion and registration of the entire data set at once. We describe an interactive tool that manages the workflow for converting urban-scale point clouds to grid-registered geometric models. Our 'user in the loop' approach lets us leverage natural human understanding of the data to bypass issues of scale.
Mobile 3D Graphics
(The Eurographics Association, 2008) Pulli, Kari; Vaarala, Jani; Miettinen, Ville; Simpson, Robert J.; Aarnio, Tomi; Callow, Mark; Maria Roussou and Jason Leigh
Mobile phone handsets are fast becoming personal computing platforms and offer exciting new opportunities for graphics applications. They present the largest ever market opportunity for the graphics industry. Handset shipments are an order of magnitude larger than PC shipments. Not surprisingly they come with significant limitations compared to traditional desktop environments. This course presents two 3D graphics APIs that address the special needs and constraints of mobile platforms and have become dominant in that space: OpenGL ES and M3G. OpenGL ES 1.1 is a lightweight version of the well-known workstation standard, offering a subset of OpenGL 1.5 capability plus support for fixed point arithmetic. OpenGL ES 2.0 brings programmable shaders into mobile devices. M3G, Mobile 3D Graphics API for Java Micro Edition augments the low-level rendering capabilities of OpenGL ES with scene graph, animation, and file format support to facilitate content production with popular tools such as Max or Maya. The second generation M3G 2.0 (still being standardized) introduces shaders to mobile Java. These APIs provide powerful graphics capabilities in a form that fits well on today's devices, both with and without a hardware floating point unit and a graphics hardware accelerator. We begin the course with a discussion of the target environments and their limitations, and general techniques for coping with these (such as fixed-point arithmetic). We continue with detailed descriptions of the functionality of OpenGL ES 1.1, 2.0, and M3G 1.1, comparing to related desktop standards as necessary and explaining what was left out and why. We will show how to use the APIs in practical examples and will provide advice on how to extract the best performance from each API and how to deal with the challenges inherent in deploying applications in the mobile space. We conclude with a description of the forthcoming M3G 2.0 standard.
Fast Force Field Approximation and its Application to Skeletonization of Discrete 3D Objects
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Brunner, D.; Brunnett, G.
In this paper we present a novel method to approximate the force field of a discrete 3d object with a time complexity that is linear in the number of voxels. We define a rule, similar to the distance transform, to propagate forces associated with boundary points into the interior of the object. The result of this propagation depends on the order in which the points of the object are processed. Therefore we analyze how to obtain an order-invariant approximation formula. With the resulting formula it becomes possible to approximate the force field and to use its features for a fast and topology preserving skeletonization. We use a thinning strategy on the body-centered cubic lattice to compute the skeleton and ensure that critical points of the force field are not removed. This leads to improved skeletons with respect to the properties of centeredness and rotational invariance.
Accurate Shadows by Depth Complexity Sampling
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Forest, Vincent; Barthe, Loic; Paulin, Mathias
The accurate generation of soft shadows is a particularly computationally intensive task. In order to reduce rendering time, most real-time and offline applications decorrelate the generation of shadows from the computation of lighting. In addition to such approximations, they generate shadows using some restrictive assumptions only correct in very specific cases, leading to penumbra over-estimation or light-leaking artifacts. In this paper we present an algorithm that produces soft shadows without exhibiting the previous drawbacks. Using a new efficient evaluation of the number of occluders between two points (i.e. the depth complexity) we either modulate direct lighting or numerically solve the rendering equation for direct illumination. Our approach approximates shadows cast by semi-opaque occluders and naturally handles area lights with spatially varying luminance. Furthermore, depending on the desired performance and quality, the resulting shadows are either very close to, or as accurate as, a ray-traced reference. As a result, the presented method is well suited to many domains, ranging from quality-sensitive to performance-critical applications.
Surface Reconstruction From Non-parallel Curve Networks
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Liu, L.; Bajaj, C.; Deasy, J. O.; Low, D. A.; Ju, T.
Building surfaces from cross-section curves has wide applications including bio-medical modeling. Previous work in this area has mostly focused on connecting simple closed curves on parallel cross-sections. Here we consider the more general problem where input data may lie on non-parallel cross-sections and consist of curve networks that represent the segmentation of the underlying object by different material or tissue types (e.g., skin, muscle, bone, etc.) on each cross-section. The desired output is a surface network that models both the exterior surface and the internal partitioning of the object. We introduce an algorithm that is capable of handling curve networks of arbitrary shape and topology on cross-section planes with arbitrary orientations. Our algorithm is simple to implement and is guaranteed to produce a closed surface network that interpolates the curve network on each cross-section. Our method is demonstrated on both synthetic and bio-medical examples.
Sketching and Composing Widgets for 3D Manipulation
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Schmidt, Ryan; Singh, Karan; Balakrishnan, Ravin
We present an interface for 3D object manipulation in which standard transformation tools are replaced with transient 3D widgets invoked by sketching context-dependent strokes. The widgets are automatically aligned to axes and planes determined by the user s stroke. Sketched pivot-points further expand the interaction vocabulary. Using gestural commands, these basic elements can be assembled into dynamic, user-constructed 3D transformation systems. We supplement precise widget interaction with techniques for coarse object positioning and snapping. Our approach, which is implemented within a broader sketch-based modeling system, also integrates an underlying widget history to enable the fluid transfer of widgets between objects. An evaluation indicates that users familiar with 3D manipulation concepts can be taught how to efficiently use our system in under an hour.
Curvature-Domain Shape Processing
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Eigensatz, Michael; Sumner, Robert W.; Pauly, Mark
We propose a framework for 3D geometry processing that provides direct access to surface curvature to facilitate advanced shape editing, filtering, and synthesis algorithms. The central idea is to map a given surface to the curvature domain by evaluating its principle curvatures, apply filtering and editing operations to the curvature distribution, and reconstruct the resulting surface using an optimization approach. Our system allows the user to prescribe arbitrary principle curvature values anywhere on the surface. The optimization solves a nonlinear least-squares problem to find the surface that best matches the desired target curvatures while preserving important properties of the original shape. We demonstrate the effectiveness of this processing metaphor with several applications, including anisotropic smoothing, feature enhancement, and multi-scale curvature editing.
Rendering Method for Flat Origami
(The Eurographics Association, 2008) Mitani, Jun; Katerina Mania and Eric Reinhard
In flat Origami (Origami which is folded flat), some cases exist that have a closed-loop in the overlap order of faces after they are folded. It is difficult to display this shape correctly on the screen when Origami is expressed by sets of plane polygons of zero thickness as is generally used in CG because all faces are placed on the same plane. In the present paper, we propose a new rendering technique to solve this problem. In the proposed method, we prepare a matrix that represents the overlap relation between two faces and a face ID buffer, the concept of which is similar to a Z buffer in the z-buffer algorithm. With this buffer, the face located in the uppermost is monitored in each pixel at the rendering stage. We render the shape on the face ID buffer using a scanline algorithm and display the folded shape by outputting the result in which the edges are extracted. Moreover, we render the shape in technical illustration style by coloring each vertex according to the number of mountain and valley folds connected to the vertex. In addition, we propose a simple pseudo shading algorithm.
Detail-In-Context Visualization for Satellite Imagery
(The Eurographics Association and Blackwell Publishing Ltd, 2008) Boettger, Joachim; Preiser, Martin; Balzer, Michael; Deussen, Oliver
We use the complex logarithm as a transformation for the visualization and navigation of highly complex satellite and aerial imagery. The resulting depictions show details and context with greatly different scales in one seamless image while avoiding local distortions. We motivate our approach by showing its relations to the ordinary perspective views and classical map projections. We discuss how to organize and process the huge amount of imagery in realtime using modern graphics hardware with an extended clipmapping technique. Finally, we provide details and experiences concerning the interpretation of and interaction with the resulting representations.
From a Light CG Framework to a strong Cannibal Experience
(The Eurographics Association, 2008) Boers, Jerke; Dobbe, Jeroen; Huijser, Remco; Bidarra, Rafael; Steve Cunningham and Lars Kjelldahl
Game development courses are being more and more deployed within computer graphics (CG) curricula. A fundamental element in the pedagogical effectiveness of such courses is the quality of the development framework provided to the students. We discuss the most important challenges faced throughout the years while using, configuring and improving the framework for our games project, and describe the solutions we came up with to resolve those issues. We conclude that a carefully designed development framework, including all underlying technology, course material and quality support, significantly determine the quality of a project-based game development course. In addition, when the teams in such projects have an interdisciplinary character, providing an effective collaboration environment is crucial for the success of team members. We believe that the key to the huge success of our games project lies, to a great extent, in the deployment of a professional working environment specifically crafted for an educational setting.
FMDistance: A Fast and Effective Distance Function for Motion Capture Data
(The Eurographics Association, 2008) Onuma, Kensuke; Faloutsos, Christos; Hodgins, Jessica K.; Katerina Mania and Eric Reinhard
Given several motion capture sequences, of similar (but not identical) length, what is a good distance function? We want to find similar sequences, to spot outliers, to create clusters, and to visualize the (large) set of motion capture sequences at our disposal. We propose a set of new features for motion capture sequences. We experiment with numerous variations (112 feature-sets in total, using variations of weights, logarithms, dimensionality reduction), and we show that the appropriate combination leads to near-perfect classification on a database of 226 actions with twelve different categories, and it enables visualization of the whole database as well as outlier detection.

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