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Item 3D Scene Comparison using Topological Graphs(The Eurographics Association, 2007) Paraboschi, L.; Biasotti, S.; Falcidieno, B.; Raffaele De Amicis and Giuseppe ContiNew technologies for shape acquisition and rendering of digital shapes have simplified the process of creating virtual scenes; nonetheless, shape annotation, recognition and manipulation of both the complete virtual scenes and even of subparts of them are still open problems. In this paper we deal with the problem of comparing two (or more) object sets, where each model is represented by an attributed graph. We will define a new distance to estimate the possible similarities among the sets of graphs and will validate our work using the shape graph [BGSF06].Item Normal Estimation for Point Clouds: A Comparison Study for a Voronoi Based Method(The Eurographics Association, 2005) Dey, Tamal K.; Li, Gang; Sun, Jian; Marc Alexa and Szymon Rusinkiewicz and Mark Pauly and Matthias ZwickerMany applications that process a point cloud data benefit from a reliable normal estimation step. Given a point cloud presumably sampled from an unknown surface, the problem is to estimate the normals of the surface at the data points. Two approaches, one based on numerical optimizations and another based on Voronoi diagrams are known for the problem. Variations of numerical approaches work well even when point clouds are contaminated with noise. Recently a variation of the Voronoi based method is proposed for noisy point clouds. The centrality of the normal estimation step in point cloud processing begs a thorough study of the two approaches so that one knows which approach is appropriate for what circumstances. This paper presents such results.Item Volume Deformation via Scattered Data Interpolation(The Eurographics Association, 2007) Correa, Carlos D.; Silver, Deborah; Chen, Min; H.-C. Hege and R. Machiraju and T. Moeller and M. SramekWith the advent of contemporary GPUs, it has been possible to perform volume deformation at interactive rates. In particular, it has been shown that deformation can be important for the purposes of illustration. In such cases, rather than being the result of a physically-based simulation, volume deformation is often goal-oriented and user-guided. For this purpose, it is important to provide the user with tools for directly specifying a deformation interactively and refine it based on constraints or user intention. In many cases, deformation is obtained based on a reference object or image. In this paper, we present a method for deforming volumetric objects based on user guided scattered data interpolation. A GPU-based implementation enables real-time manipulation of 2D images and volumes. We show how this approach can have applications in scientific illustration, volume exploration and visualization, generation of animations and special effects, among others.Item Stippling and Silhouettes Rendering in Geometry-Image Space(The Eurographics Association, 2005) Yuan, Xiaoru; Nguyen, Minh X.; Zhang, Nan; Chen, Baoquan; Kavita Bala and Philip DutreWe present a novel non-photorealistic rendering method that performs all operations in a geometry-image domain. We first apply global conformal parameterization to the input geometry model and generate corresponding geometry images. Strokes and silhouettes are then computed in the geometry-image domain. The geometry-image space provides combined benefits of the existing image space and object space approaches. It allows us to take advantage of the regularity of 2D images and yet still have full access to the object geometry information. A wide range of image processing tools can be leveraged to assist various operations involved in achieving non-photorealistic rendering with coherence.Item Realistic Soft Shadows by Penumbra-Wedges Blending(The Eurographics Association, 2006) Forest, Vincent; Barthe, Loïc; Paulin, Mathias; Marc Olano and Philipp SlusallekRecent real-time shadow generation techniques try to provide shadows with realistic penumbrae. However, most techniques are whether non-physically based or too simplified to produce convicing results. The penumbra-wedges algorithm is a physical approach based on the assumption that penumbrae are non-overlapping. In this paper, we propose an algorithm that takes the advantages of the penumbra-wedges method but solves the "non-overlapping" limitation. We first compute the light occlusion regions per fragment. Then we use this information to detect the areas where penumbrae are overlapping and we perform a realistic penumbra blending.Item Defining and Computing Curve-skeletons with Medial Geodesic Function(The Eurographics Association, 2006) Dey, Tamal K.; Sun, Jian; Alla Sheffer and Konrad PolthierMany applications in geometric modeling, computer graphics, visualization and computer vision benefit from a reduced representation called curve-skeletons of a shape. These are curves possibly with branches which compactly represent the shape geometry and topology. The lack of a proper mathematical definition has been a bottleneck in developing and applying the the curve-skeletons. A set of desirable properties of these skeletons has been identified and the existing algorithms try to satisfy these properties mainly through a procedural definition. We define a function called medial geodesic on the medial axis which leads to a methematical definition and an approximation algorithm for curve-skeletons. Empirical study shows that the algorithm is robust against noise, operates well with a single user parameter, and produces curve-skeletons with the desirable properties. Moreover, the curveskeletons can be associated with additional attributes that follow naturally from the definition. These attributes capture shape eccentricity, a local measure of how far a shape is away from a tubular one.Item An Adaptive MLS Surface for Reconstruction with Guarantees(The Eurographics Association, 2005) Dey, Tamal K.; Sun, Jian; Mathieu Desbrun and Helmut PottmannRecent work have shown that moving least squares (MLS) surfaces can be used effectively to reconstruct surfaces from possibly noisy point cloud data. Several variants of MLS surfaces have been suggested, some of which have been analyzed theoretically for guarantees. These analyses, so far, have assumed uniform sampling density. We propose a new variant of the MLS surface that, for the first time, incorporates local feature sizes in its formulation, and we analyze it for reconstruction guarantees using a non-uniform sampling density. The proposed variant of the MLS surface has several computational advantages over existing MLS methods.Item The Aesthetics of Graph Visualization(The Eurographics Association, 2007) Bennett, Chris; Ryall, Jody; Spalteholz, Leo; Gooch, Amy; Douglas W. Cunningham and Gary Meyer and Laszlo NeumannThe discipline of graph visualization produces pictorial representations of node link structures. Much effort has been directed toward making such diagrams visually pleasing. A variety of aesthetic heuristics have been proposed, with the assumption that these will improve readability and understanding. We look at a perceptual basis for these heuristics, including Gestalt principles and Norman s emotional design framework. Next, we review the work to date on aesthetic heuristics and examine what has been done to evaluate these heuristics. We summarize this in a framework that outlines graph drawing heuristics, their perceptual basis, and evaluation status.Item GPU-assisted Positive Mean Value Coordinates for Mesh Deformations(The Eurographics Association, 2007) Lipman, Yaron; Kopf, Johannes; Cohen-Or, Daniel; Levin, David; Alexander Belyaev and Michael GarlandIn this paper we introduce positive mean value coordinates (PMVC) for mesh deformation. Following the observations of Joshi et al. [JMD*07] we show the advantage of having positive coordinates. The control points of the deformation are the vertices of a "cage" enclosing the deformed mesh. To define positive mean value coordinates for a given vertex, the visible portion of the cage is integrated over a sphere. Unlike MVC [JSW05], PMVC are computed numerically. We show how the PMVC integral can be efficiently computed with graphics hardware. While the properties of PMVC are similar to those of Harmonic coordinates [JMD*07], the setup time of the PMVC is only of a few seconds for typical meshes with 30K vertices. This speed-up renders the new coordinates practical and easy to use.Item Bringing the Semantics into Digital Shapes: the AIM@SHAPE Approach(The Eurographics Association, 2007) Falcidieno, Bianca; Raffaele De Amicis and Giuseppe ContiThis presentation describes the main objectives and achievements of the European Network of Excellence AIM@SHAPE. This NoE is aimed to advance research in the direction of semantic-based shape representations and tools able to acquire, build, transmit and process shapes with their associated knowledge. Acting on a multi-disciplinary research field, AIM@SHAPE deeply integrates geometry processing, computer graphics and vision with knowledge technologies. The core of the integration resides in the homogenisation of the approach to modelling shapes and their associated semantics using knowledge formalisation mechanisms: metadata and ontology. A main objective is also to develop an innovative e-science platform for modelling, processing and sharing digital shapes, called the Digital Shape Workbench (DSW). Through the definition of general and specific shape ontologies, the DSW is a framework able to store shapes, tools, and publications along with the knowledge related to them.