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Item Afrigraph: The African Computer Graphics Association and its Activities(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gain, J.; Strasser, W.; Hardy, A.; Marais, P.Item Meshless Shape and Motion Design for Multiple Deformable Objects(The Eurographics Association and Blackwell Publishing Ltd, 2010) Adams, B.; Wicke, M.; Ovsjanikov, M.; Wand, M.; Seidel, H.-P.; Guibas, L. J.We present physically based algorithms for interactive deformable shape and motion modelling. We coarsely sample the objects with simulation nodes, and apply a meshless finite element method to obtain realistic deformations at interactive frame rates. This shape deformation algorithm is then used to specify keyframe poses and a smooth interpolating motion is obtained by solving for an energy-minimizing trajectory. We show how to handle collisions between different deformable objects as well as with static or moving scene objects. Secondary motion is added as a post-process by running a meshless elastic solid simulation. We enforce precomputed trajectories using control forces computed using shape matching. Key to the efficiency of our method is a sparse deformation representation and an adaptive optimization algorithm that automatically introduces new degrees of freedom in problematic regions. An accurate temporal interpolation scheme that exactly recovers rigid motions keeps the number of unknowns low and achieves realistic deformations with very few keyframes. We also show how the algorithm allows combining purely physical simulation with keyframe-based scripted animation. The presented results illustrate that our framework can handle complex shapes at interactive rates, making it a valuable tool for animators to realistically model deformable 3D shapes and their motion.Item State of the Art in Example-Based Motion Synthesis for Virtual Characters in Interactive Applications(The Eurographics Association and Blackwell Publishing Ltd, 2010) Pejsa, T.; Pandzic, I.S.Animated virtual human characters are a common feature in interactive graphical applications, such as computer and video games, online virtual worlds and simulations. Due to dynamic nature of such applications, character animation must be responsive and controllable in addition to looking as realistic and natural as possible. Though procedural and physics-based animation provide a great amount of control over motion, they still look too unnatural to be of use in all but a few specific scenarios, which is why interactive applications nowadays still rely mainly on recorded and hand-crafted motion clips. The challenge faced by animation system designers is to dynamically synthesize new, controllable motion by concatenating short motion segments into sequences of different actions or by parametrically blending clips that correspond to different variants of the same logical action. In this article, we provide an overview of research in the field of example-based motion synthesis for interactive applications. We present methods for automated creation of supporting data structures for motion synthesis and describe how they can be employed at run-time to generate motion that accurately accomplishes tasks specified by the AI or human user.Item Adaptive and Feature-Preserving Subdivision for High-Quality Tetrahedral Meshes(The Eurographics Association and Blackwell Publishing Ltd, 2010) Burkhart, D.; Hamann, B.; Umlauf, G.We present an adaptive subdivision scheme for unstructured tetrahedral meshes inspired by the -subdivision scheme for triangular meshes. Existing tetrahedral subdivision schemes do not support adaptive refinement and have traditionally been driven by the need to generate smooth three-dimensional deformations of solids. These schemes use edge bisections to subdivide tetrahedra, which generates octahedra in addition to tetrahedra. To split octahedra into tetrahedra one routinely chooses a direction for the diagonals for the subdivision step. We propose a new topology-based refinement operator that generates only tetrahedra and supports adaptive refinement. Our tetrahedral subdivision algorithm is motivated by the need to have one representation for the modeling, the simulation and the visualization and so to bridge the gap between CAD and CAE. Our subdivision algorithm design emphasizes on geometric quality of the tetrahedral meshes, local and adaptive refinement operations, and preservation of sharp geometric features on the boundary and in the interior of the physical domain.Item Bidirectional Texture Function Compression Based on Multi-Level Vector Quantization(The Eurographics Association and Blackwell Publishing Ltd, 2010) Havran, V.; Filip, J.; Myszkowski, K.The Bidirectional Texture Function (BTF) is becoming widely used for accurate representation of real-world material appearance. In this paper a novel BTF compression model is proposed. The model resamples input BTF data into a parametrization, allowing decomposition of individual view and illumination dependent texels into a set of multi-dimensional conditional probability density functions. These functions are compressed in turn using a novel multi-level vector quantization algorithm. The result of this algorithm is a set of index and scale code-books for individual dimensions. BTF reconstruction from the model is then based on fast chained indexing into the nested stored code-books. In the proposed model, luminance and chromaticity are treated separately to achieve further compression. The proposed model achieves low distortion and compression ratios 1:233-1:2040, depending on BTF sample variability. These results compare well with several other BTF compression methods with predefined compression ratios, usually smaller than 1:200. We carried out a psychophysical experiment comparing our method with LPCA method. BTF synthesis from the model was implemented on a standard GPU, yielded interactive framerates. The proposed method allows the fast importance sampling required by eye-path tracing algorithms in image synthesis.Item Constrained Texture Mapping using Image Warping(The Eurographics Association and Blackwell Publishing Ltd, 2010) Seo, H.; Cordier, F.We introduce in this paper a new method for smooth foldover-free warping of images. It allows users to specify the constraints in two different ways: positional constraints to constrain the position of points in the image and gradient constraints to constrain the orientation and scaling of some parts of the image. We then show how our method is used for texture mapping with hard constraints. We start with an unconstrained planar embedding of the target mesh calculated with conventional methods. In order to obtain a mapping that satisfies the user-defined constraints, we use our warping method to align the features of the texture image with those of the unconstrained embedding. Compared to previous work, our method generates a smoother texture mapping and offers higher level of control for defining the constraints.Item Editorial(The Eurographics Association and Blackwell Publishing Ltd, 2010) Scopigno, Roberto; Groeller, EduardItem Automatic Transfer Function Specification for Visual Emphasis of Coronary Artery Plaque(The Eurographics Association and Blackwell Publishing Ltd, 2010) Glasser, S.; Oeltze, S.; Hennemuth, A.; Kubisch, C.; Mahnken, A.; Wilhelmsen, S.; Preim, B.Cardiovascular imaging with current multislice spiral computed tomography (MSCT) technology enables a non-invasive evaluation of the coronary arteries. Contrast-enhanced MSCT angiography with high spatial resolution allows for a segmentation of the coronary artery tree. We present an automatically adapted transfer function (TF) specification to highlight pathologic changes of the vessel wall based on the segmentation result of the coronary artery tree. The TFs are combined with common visualization techniques, such as multiplanar reformation and direct volume rendering for the evaluation of coronary arteries in MSCT image data. The presented TF-based mapping of CT values in Hounsfield Units (HU) to color and opacity leads to a different color coding for different plaque types. To account for varying HU values of the vessel lumen caused by the contrast medium, the TFs are adapted to each dataset by local histogram analysis. We describe an informal evaluation with three board-certified radiologists which indicates that the represented visualizations guide the user s attention to pathologic changes of the vessel wall as well as provide an overview about spatial variations.Item A Grasping Hand, Made of Small Stones(The Eurographics Association and Blackwell Publishing Ltd, 2010) Peytavie, Adrien; Galin, Eric; Grosjean, Jerome; Merillou, StephaneItem Hybrid Booleans(The Eurographics Association and Blackwell Publishing Ltd, 2010) Pavic, Darko; Campen, Marcel; Kobbelt, LeifIn this paper, we present a novel method to compute Boolean operations on polygonal meshes. Given a Boolean expression over an arbitrary number of input meshes we reliably and efficiently compute an output mesh which faithfully preserves the existing sharp features and precisely reconstructs the new features appearing along the intersections of the input meshes. The term hybrid applies to our method in two ways: First, our algorithm operates on a hybrid data structure which stores the original input polygons (surface data) in an adaptively refined octree (volume data). By this we combine the robustness of volumetric techniques with the accuracy of surface-oriented techniques. Second, we generate a new triangulation only in a close vicinity around the intersections of the input meshes and thus preserve as much of the original mesh structure as possible (hybrid mesh). Since the actual processing of the Boolean operation is confined to a very small region around the intersections of the input meshes, we can achieve very high adaptive refinement resolutions and hence very high precision. We demonstrate our method on a number of challenging examples.