GRAPP 2010 Abstracts

Area 1 - Geometry and Modeling
Full Papers Short Papers
Area 2 - Rendering
Full Papers Short Papers
Area 3 - Animation and Simulation
Full Papers Short Papers
Area 4 - Interactive Environments
Full Papers Short Papers

Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 9
Title:

A Framework for Data-Driven Progressive Mesh Compression
Authors:

Florent Dupont, Guillaume Lavoué, Gabriel Cirio, Guillaume Lavoué and Florent Dupont
Abstract: Progressive mesh compression techniques have reached very high compression ratios. However, these techniques usually do not take into account associated properties of meshes such as colors or normals, no matter their size, nor do they try to improve the quality of the intermediate decompression meshes. In this work, we propose a framework that uses the associated properties of the mesh to drive the compression process, resulting in an improved quality of the intermediate decompression meshes. Based on a kd-tree geometry compression algorithm, the framework is generic enough to allow any property or set of properties to drive the compression process provided the user defines a distance function for each property. The algorithm builds the kd-tree structure using a voxelisation process, which recursively separates the set of vertices according to the associated properties distances. We evaluate our method by comparing its compression ratios to recent algorithms. In order to evaluate the visual quality of the intermediate meshes, we carried a perceptive evaluation with human subjects. Results show that at equal rates, our method delivers an overall better visual quality. The algorithm is particularly well suited for the compression of meshes where geometry and topology play a secondary role compared to associated properties, such as with many scientific visualization models.
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Paper Nr: 10
Title:

NORMAL SYNTHESIS ON RGBN IMAGES
Authors:

Thiago Pereira and Luiz R. Velho
Abstract: In this work, we synthesize normals and color to add geometric details to an RGBN image (image with a color and a normal channel). Existing modeling and image processing tools are not apt to edit RGBN images directly. Since high resolution RGBN images can be obtained using photometric stereo, we used them as full models and as exemplars in a Texture from Example synthesis. Our method works on RGBN images by combining the normals from two bands: base shape and details. We use a high pass filter to extract a texture exemplar, which is synthesized over the model’s smooth normals, taking into account foreshortening corrections. We also discuss conditions on the exemplars and models that guarantee that the resulting normal image is a realizable surface.
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Paper Nr: 18
Title:

TopMesh: A Tool for Extracting Topological Information From Non-Manifold Objects
Authors:

Laura Papaleo, Leila De Floriani and Annie Hui
Abstract: We present TopMesh, a tool for extracting topological information from non-manifold three-dimensional objects with parts of non-uniform dimensions. The boundary of such objects is discretized as a mesh of triangles and of dangling edges, representing one-dimensional parts of the object. The geometrical and topological information extracted include the number of elements in the mesh, the number of non-manifold singularities and the Betti numbers, which characterize the topology of an object independently of the discretization of its boundary. TopMesh also computes a decomposition of the mesh into connected parts of uniform dimension, into edge-connected components formed by triangles, and into oriented edge-connected sub-meshes. We describe the functionalities of TopMesh and the algorithms implementing them
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Paper Nr: 20
Title:

Viewpoint Entropy-driven Simplification Method for Textured Triangle Meshes
Authors:

Carlos González, Pascual Castelló, Miguel Chover, Mateu Sbert and Miquel Feixas
Abstract: This paper proposes a viewpoint-driven simplification method for textured triangle meshes. Models used in interactive applications are usually composed of geometric meshes with textures. Thus, textures play an important role in the final aspect of the simplified models. This method considers the texture shape in the error metric. Entropy, a concept from Information Theory, is used in this error metric. We show in the experiments that this method produces simplifications that preserve textures better than the methods that do not take them into account. Therefore, great distortions when applying the textures are avoided.
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Paper Nr: 43
Title:

Projected Gauss-Seidel Subspace Minimization Method for Interactive Rigid Body Dynamics
Authors:

Morten Silcowitz, Morten Silcowitz, Sarah Niebe and Kenny Erleben
Abstract: In interactive physical simulation, contact forces are applied to prevent rigid bodies from penetrating and to control slipping between bodies. Accurate contact force determination is a computationally hard problem. Thus, in practice one trades accuracy for performance. This results in visual artifacts such as viscous or damped contact response. In this paper, we present a new approach to contact force determination. We formulate the contact force problem as a nonlinear complementarity problem, and discretize the problem to derive the Projected Gauss-Seidel method. We combine the Projected Gauss--Seidel method with a subspace minimization method. Our new method shows improved qualities and superior convergence properties for specific configurations.
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Paper Nr: 68
Title:

A Practical Approach for applying Non-Linear Dynamics to Particle Systems
Authors:

Athanasios Vogiannou, Kostantinos Moustakas, Dimitrios Tzovaras and Michael G. Strintzis
Abstract: In this paper we present a new method for approximating non-linear dynamics in deformable simulationsbased on a full cubic polynomial formulation of the inter-particle force. The proposed approach is a non-physical extension of the well known St Venant Kirchhoff force, focusing on practical considerations about the behavior of the deformable model. Therefore it is very useful for simulating and controlling non-linear stretching and compressing properties of deformable models in applications where the computation time comprises a major constraint. The presented force model can be easily implemented by the widely used particle systems and can be parameterized based on a direct relation to spring models. We show that the non linear stretching behavior of the proposed model is required for simulations where the external forces which interact with the models are large in scale, while the performance of the presented method is comparable to simple mass-spring systems.
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Paper Nr: 75
Title:

Temporal Photon Differentials
Authors:

L. Schj, Jon Sporring, Kenny Erleben, Lars Schjøth and Jeppe R. Frisvad
Abstract: The finite frame rate also used in computer animated films is cause of adverse temporal aliasing effects. Most noticeable of these is a stroboscopic effect that is seen as intermittent movement of fast moving illumination. This effect can be mitigated using non-zero shutter times, effectively, constituting a temporal smoothing of rapidly changing illumination. In global illumination temporal smoothing can be achieved with distribution ray tracing (Cook et al., 1984). Unfortunately, this, and resembling methods, requires a high temporal resolution as samples has to be drawn from in-between frames. We present a novel method which is able to produce high quality temporal smoothing for indirect illumination without using in-between frames. Our method is based on ray differentials (Igehy, 1999) as it has been extended in (Sporring et al., 2009). Light rays are traced as bundles creating footprints, which are used to reconstruct indirect illumination. These footprints expand into the temporal domain such that light rays interacting with non-static scene elements draw a path reacting to the elements movement.
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Short Papers
Paper Nr: 16
Title:

3D RECONSTRUCTION FROM LINE DRAWINGS
Authors:

Lars H. Wendt, Arjan Kuijper, André Stork, Lars Henning Wendt, André Stork, Arjan Kuijper and Dieter Fellner
Abstract: In this work we introduce an approach for reconstructing digital 3D models from multiple perspective line drawings. One major goal is to keep the required user interaction simple and at a minimum, while making no constraints to the objects shape. Such a system provides a useful extension for digitalization of paper-based styling concepts, which today is still a time consuming process. In the presented method the line drawings are first decomposed in curves assembling a network of curves. In a second step, the positions for the endpoints of the curves are determined in 3D, using multiple sketches and a virtual camera model given by the user. Then the shapes of the 3D curves between the reconstructed 3D endpoints are inferred. This leads to a network of 3D curves, which can be used for first visual evaluations in 3D. During the whole process only little user interaction is needed, which takes place only in the pre- and post-processing phases. The approach has been applied on multiple sketches and it is shown that the approach creates plausible results within reasonable timing.
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Paper Nr: 17
Title:

3D VOLUME DATA SEGMENTATION FROM SUPERQUADRIC TENSOR ANALYSIS
Authors:

Sang Min Yoon, Sang M. Yoon and Arjan Kuijper
Abstract: The segmentation of 3D target objects into coherent subregions is one of the most important issues in computer graphics and computer vision as it is applied in many applications, such as medical model visualization and analysis, 3D model retrieval and recognition, skeleton extraction, and collision detection. The goal of 3D segmentation is to separate the volume or mesh data into several subregions which have similar characteristics. In this paper, we present an efficient and accurate 3D model segmentation methodology by iteratively merging and splitting subregions in a 3D model using diffusion tensor fields. Our innovative 3D model segmentation system consists of two steps: i) the ellipsoidal decomposition of unorganized 3D object using properties of three dimensional second-order diffusion tensor fields, and ii) The iteratively merging and splitting of subregions of the 3D model by measuring the similarity between neighboring regions. Experimental results are conducted to evaluate the performance of our methodology using 3D models from well-known databases and 3D target objects that are econstructed from image sequences. They show an efficient and robust segmentation into visually coherent sub regions.
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Paper Nr: 25
Title:

SWEEPING BASED CONTROLLABLE SURFACE BLENDING
Authors:

Lihua You, Hassan Ugail, Baoping Tang, Xiangyu You and Jian J. Zhang
Abstract: In this paper, we propose a novel sweeping surface based blending method. A generator defined by the solution of a vector-valued fourth order ordinary differential equation is swept along the two trimlines, which meets the boundary tangent constraints of the primary surfaces at the trimlines. The blending surface generated therefore satisfies both the positional and tangential continuity constraints at the interfaces between the primary surfaces and the blending surface. Since the vector-valued shape control parameters are embedded in the blending surface, its shape can be effectively controlled and manipulated by adjusting these vector-valued shape control parameters. Several surface blending examples are given to demonstrate the applications of the proposed method.
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Paper Nr: 26
Title:

MANIPULATION OF PARAMETRIC SURFACES THROUGH A SIMPLE DEFORMATION ALGORITHM
Authors:

Lihua You, Hassan Ugail, Xiangyu You, Ehtzaz A. Chaudhry and Jian J. Zhang
Abstract: In this paper, we present a novel but simple physics based method to manipulate parametric surfaces. This method can deal with local deformations with an arbitrarily complicated boundary shape. We firstly map a deformation region of a 3D surface to a circle on a 2D parametric plane. Then we derive an approximate analytical solution of a set of fourth order partial differential equations subjected to sculpting forces and the boundary conditions of the circle. With the obtained solution, we show how to create a deformed surface and how sculpting forces and the shape control parameters affect the shape of a deformed surface. Finally, we provide some examples to demonstrate the applications of our proposed method in surface manipulation.
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Paper Nr: 34
Title:

A Geometric Approach to Curvature Estimation on Triangulated 3D Shapes
Authors:

Mohammed Mesmoudi, Leila De Floriani and Paola Magillo
Abstract: We present a geometric approach to define discrete normal, principal, Gaussian and mean curvatures, that we call Ccurvature. Our approach is based on the notion of concentrated curvature of a polygonal line and a simulation of rotation of the normal plane of the surface at a point. The advantages of our approach is its simplicity and its natural meaning. A comparison with widely-used discrete methods is presented.
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Paper Nr: 51
Title:

DECOMPOSITION OF A 3D TRIANGULAR MESH INTO QUADRANGULATED PATCHES
Authors:

Roseline Bénière, Gilles Gesquière, Gérard Subsol, William Puech and François L. Breton
Abstract: In this paper we present a method to decompose a 3D triangular mesh into a set of quadrangulated patches. This method consists in merging triangles to obtain quads. The quads are then grouped together to compose quadrangulated areas and patches. Unlike many methods of remeshing, this method does not move the vertices of the original triangular mesh. Quadrangulated patches extracted can then be used as a support of a parametric function or of a subdivision scheme.
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Paper Nr: 52
Title:

Controlled and Adaptive Mesh Zippering
Authors:

Stefano Marras, Fabio Ganovelli, Roberto Scopigno, Stefano Marras, Paolo Cignoni and Riccardo Scateni
Abstract: Merging meshes together is recurrent need in geometry modeling and it a critical step in the 3D acquisition pipeline, where it is used for building a single mesh from several range scans. Zippering has been a pioneering simple and effecting solution to merging, and it consists of simply stitching the meshes together along their border. In this paper we propose a new extended version of the zippering algorithm which enables the user to control the quality of the resulting mesh by introducing quality criteria in the selection of redundant data, and allow to zip together meshes with different granularity by an ad hoc refinement algorithm.
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Paper Nr: 73
Title:

SYNTHESIS OF BEZIER SURFACES ON THE GPU
Authors:

Raquel Concheiro, Montserrat Bóo and Margarita Amor
Abstract: Bezier surfaces are one of the most useful primitives employed for high quality modeling in CAD/CAM tools and graphics software.Tradicionally, the Bezier representations are usually tessellated on the CPU (Central Processing Unit) and the set of generated triangles is sent to the GPU (Graphic Processing Unit). The CPU-GPU bus can become a bottleneck in this approach due to the large number of triangles generated for high quality models. In this paper we present two proposals for synthesizing the B ezier models directly in the GPU. With this strategy the compact representation associated with the Bezier models is sent to the GPU where the rendering is performed. The first proposal is based on the exploitation of the vertex shader to perform the tessellation. In this case a parametric map guides the computation of the final coordinates of a set of virtual vertices. Our second proposal is based on the efficient exploitation of the geometry shader capabilities to perform the tessellation in a direct way. Tests performed show that both proposals produce high quality images and promising results for real time rendering of complex parametric models.
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Paper Nr: 79
Title:

Bubbleworld Builder - 3D Modelling Using Two-Touch and Sketch Interaction
Authors:

Amit Joshi, Glen Robertson, Burkhard Wuensche and Beryl Plimmer
Abstract: Commercial 3D modeling applications tend to be difficult and time consuming to use due to complex interfaces and functionality. In this paper we present a simple and intuitive interface for modeling “blobby” 3D objects using touch input. Objects are defined by sketching and modifying contours of cross-sectional slices. Two-touch interactions are used to zoom, rotate and slice the object. The resulting application allows rapid creation of 3D models and looks promising for medical imaging applications. A drawback is that intuitiveness depends on a user’s mental abilities such as 3D vision and the ability to develop a mental model and compare it with visual data.
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Paper Nr: 4
Title:

Comparison in the Hausdorff Metric of Reconstruction of 3D Urban Terrain by Four Procedures
Authors:

Dimitri Bulatov and John E. Lavery
Abstract: We computationally compare four procedures, namely, alpha-shapes, iso-surface extraction, gridfit and L_1 splines for geometric reconstruction of 3D urban structures represented by irregular point clouds with abrupt changes in density. For significant numbers of outliers, L_1 splines produce the most accurate reconstructions both visually and when measured analytically in the Hausdorff metric but are more computationally expensive than the other three procedures.
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Paper Nr: 35
Title:

PROCEDURAL MODELLING OF MONUMENTAL BUILDINGS FROM TEXTUAL DESCRIPTIONS
Authors:

António Coelho, Luís Paulo Reis, Roberto Rodrigues, Luís Paulo Reis and António Coelho
Abstract: The generation of three-dimensional models of urban environments using procedural modelling is presented as being a solution which allows financial and temporal gains, maintaining an acceptable visual fidelity level. Nevertheless, the modelling of anchor buildings (or monumental), identifying certain urban areas, needs a more careful modelling due to the high level of detail necessary, using, generally, manual modelling. We present an automation proposal of the building modelling process through the introduction of additional knowledge from textual descriptions in a procedural modelling system. The results show that the data model is flexible enough to build distinct models of churches. The data model can also provide an initial structure for high level modelling, providing the global shape for the building and the location of doors, windows or other structures. High detailed models can be built from this initial structure. The results demonstrate also that it is possible to create a 3D model from a text and thus permitting that non-specialised users may increase effectiveness using a procedural modelling system.
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Paper Nr: 48
Title:

Vector Segmentation of Volumetric Image Data: Tetrahedral Meshing Constrained by Image Edges
Authors:

Michal Spanel, Miroslav Svub, Vit Stancl and Premysl Krsek
Abstract: In this paper, a vector segmentation algorithm of volumetric data based on the 3D Delaunay triangulation is presented. A modified variational meshing method is used to adapt tetrahedral mesh to the underlying CT/MRI volumetric data. Moreover, to classify tetrahedra in the mesh into regions whose characteristics are similar, a clustering scheme viewing the mesh as undirected graph with edges weighted according to similarity of tetrahedra is discussed.
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Paper Nr: 58
Title:

Calibration-free Markerless Augmented Reality in Monocular Laparoscopic Cholecystectomy
Authors:

Haroun Djaghloul, Jean-Pierre Jessel and Batouche Mohamed
Abstract: In this paper we present an augmented reality system for laparoscopic cholecystectomy video sequences enhancing. Augmented reality allows surgeons to view, in transparency, occluded anatomical and pathological structures constructed preoperatively using medical images such as MRI or CT-Scan. The deformable nature of digestive organs leads to a high dimensionality N-degrees of freedom detection and tracking problem. We describe a knowledge-based construction method of powerful statistical color models for anatomical structures and surgical instruments classification from professional high-quality videos and images dataset semi-automatically labelled pixels. Thanks to a new wavelet based multi-resolution analysis of the virtual reality models and the anatomical color space; we can detect and track digestive organs to ensure marker-less laparoscopic monocular camera pose and preoperative 3D model registration though environment complexity and rapid motion due to intra-operative cardio-respiratory activity and surgical instruments interaction. A new multi-resolution 2D/3D registration method using particles swarm optimisation (PSO) is proposed with an original generalized registration criteria. Results are shown on both synthetic and real data.
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Paper Nr: 72
Title:

Marching Cubes in an Unsigned Distance Field for Surface Reconstruction from Unorganized Point Sets
Authors:

John Congote, Oscar Ruiz-Salguero, Jorge Posada, Javier Barandiaran, Aitor Moreno and Iñigo Barandiaran
Abstract: Surface reconstruction from unorganized point set is a common problem in computer graphics. Generation of the signed distance field from the point set is a common methodology for the surface reconstruction. The reconstruction of implicit surfaces is made with the algorithm of marching cubes, but the distance field of a point set can not be processed with marching cubes because the unsigned nature of the distance. We propose an extension to the marching cubes algorithm allowing the reconstruction of 0-level iso-surfaces in an unsigned distance field. We calculate more information inside each cell of the marching cubes lattice and then we extract the intersection points of the surface within the cell then we identify the marching cubes case for the triangulation. Our algorithm generates good surfaces but the presence of ambiguities in the case selection generates some topological mistakes.
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Paper Nr: 77
Title:

Coons Triangular Bézier surfaces
Authors:

Ana M Arnal and Ana Lluch

Abstract: In this paper we give some different surface generation methods starting out from prescribed boundary curves. If the boundary control points are known it is natural to think of Coons patches, a popular solution of the problem of finding a surface given its boundary curves. We have developed three methods to generate triangular patches given the boundary curves. First we give a discrete version of the triangular Coons patch. A second method lets us to find the extremals of a functional as a solution of a linear system of the control points. That functional is the one that minimizes the Coons patch. The third method makes it possible to build a Bézier triangle by means of a mask deduced from the characterization of cubical extremals of the functional.
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Paper Nr: 80
Title:

EXPLICIT SOLUTION FOR THE MINIMUM DISTANCE BETWEEN TWO SOLID SEMI-INFINITE CIRCULAR CONES

Authors:

Baruch Karlin
Abstract: Multi-body kinematics and object rendering often involve minimum distance calculations. Explicit solutions exist for the distance between spheres, cylinders and other simple objects. Deriving the minimum distance between cones requires numerical minimization or geometrical approximations combined with analytical solutions for the simpler objects. This paper describes an explicit solution for the minimum distance between two solid semi-infinite circular cones. The method combines geometrical reasoning with analytical derivation. The solution also includes the location of the intersection points. Solution regions are identified and discussed. A numerical method based on minimizing the distance between two cone generators was used as part of the verification process. The exact solution was compared to results of approximation by regular polytopes. The explicit solution is robust, independent of coordinate system and invariant under rigid translation and rotation of the setup.
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Area 2 - Rendering

Full Papers
Paper Nr: 19
Title:

Modeling Wavelength-Dependent BRDFs As Factored Tensors For Real-Time Spectral Rendering
Authors:

Karsten Schwenk, Ulrich Bockholt and Arjan Kuijper
Abstract: 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. In this paper we show how to represent wavelength-dependent BRDFs as factored tensors. We use this representation for real-time spectral rendering on modern graphics hardware. Strong data compression and fast rendering times are achieved for mostly diffuse and moderately glossy isotropic surfaces. The method can handle high-resolution tabulated BRDFs, including non-reciprocal ones, which makes it well-suited for measured data. We analyze our approach numerically and visually. One area of application for our research is virtual design applications that require high color fidelity at interactive frame rates.
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Paper Nr: 55
Title:

Spatial Color Confidence for Physically Based Rendering Settings on LC Displays
Authors:

Jörg Koch, Niklas Henrich and Stefan Müller
Abstract: Color confidence is crucial regarding physically-based rendering settings in order to produce most promising visual results. Display characterization and in particular spatial inhomogeneity correction is often neglected in physically-based rendering applications, yet, are important to achieve color confidence. By evaluating relevant display characteristics, this paper recommends a strategy for selecting the most suitable characterization model for a given device. We indicate the importance of correcting spatial inhomogeneity and, on that account, provide an extension to the applied characterization models. All characterization models as well as our proposed extensions are implemented using modern graphics hardware, therefore, applicable to real time applications. The focus is on finding an optimal characterization model which can achieve color confidence across the display while reducing characterization time and effort. All models are created using a common, single point, consumer measurement device and applied to two LC display.
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Paper Nr: 57
Title:

Relief mapping on cubic cell complexes
Authors:

Karl Apaza, Karl Apaza and Carlos Andujar
Abstract: In this paper we present an algorithm for parameterizing arbitrary surfaces onto a quadrilateral domain defined by a collection of cubic cells. The parameterization inside each cell is implicit and thus requires storing no texture coordinates. Based upon this parameterization, we propose a compact representation of geometric and appearance information of complex models. The representation consists of a set of cubic cells (providing a coarse representation of the object) together with a collection of distance maps (encoding fine geometric detail inside each cell). Our new representation has similar uses than geometry images, but it requires storing a single distance value per texel instead of full vertex coordinates. When combined with color and normal maps, our compact representation can be used to render an approximation of the model through an output-sensitive relief mapping algorithm, thus being specially amenable for GPU raytracing.
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Paper Nr: 65
Title:

An Advanced Volume Raycasting Technique using GPU Stream Processing
Authors:

Jörg Mensmann, Timo Ropinski and Klaus Hinrichs
Abstract: GPU-based raycasting is the state-of-the-art rendering technique for interactive volume visualization. The ray traversal is usually implemented in a fragment shader, utilizing the hardware in a way that was not originally intended. New programming interfaces for stream processing, such as CUDA, support a more general programming model and the use of additional device features, which are not accessible through traditional shader programming. In this paper we propose a slab-based raycasting technique that is modeled specifically to use these features to accelerate volume rendering. This technique is based on experience gained from comparing fragment shader implementations of basic raycasting to implementations directly translated to CUDA kernels. The comparison covers direct volume rendering with a variety of optional features, e.g., gradient and lighting calculations. Our findings are supported by benchmarks of typical volume visualization scenarios. We conclude that new stream processing models can only gain a small performance advantage when directly porting the basic raycasting algorithm. However, they can be advantageous through novel acceleration methods which use the hardware features not available to shader implementations.
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Paper Nr: 74
Title:

Extending Revised Affine Arithmetic for Fast Reliable Ray-tracing of Procedurally Defined Implicit Surfaces
Authors:

Oleg Fryazinov, Peter Comninos and Alexander Pasko
Abstract: Fast and reliable rendering of implicit surfaces is an important research area in the field of implicit modelling. Direct rendering, namely ray-tracing, is shown to be a suitable technique for obtaining good-quality visualisations of implicit surfaces. We present a technique for reliable ray-tracing of arbitrary procedurally defined implicit surfaces by using a modification of Affine Arithmetic called Revised Affine Arithmetic. A wide range of procedurally defined implicit objects can be rendered using this technique including polynomial surfaces, constructive solids, pseudo-random objects, procedurally defined microstructures, and others. We compare our technique with other reliable techniques based on Interval and Affine Arithmetic to show that our technique provides the fastest, while still reliable, ray-surface intersections and ray-tracing. We also suggest possible modifications for the GPU implementation of this technique for real-time rendering of relatively simple implicit models and for near real-time rendering of complex implicit models.
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Short Papers
Paper Nr: 8
Title:

Distributed Volume Rendering for Scalable High-Resolution Display Arrays
Authors:

Nicholas Schwarz and Jason Leigh
Abstract: This work presents a distributed image-order volume rendering approach for scalable high-resolution displays. This approach preprocesses data into a conventional hierarchical structure which is distributed across the local storage of a distributed-memory cluster. The cluster is equipped with graphics cards capable of hardware accelerated texture rendering. The novel contribution of this work is its unique data management scheme that spans both GPU and CPU memory using a multi-level cache and distributed shared-memory system. Performance results show that the system scales as output resolution and cluster size increase. An implementation of this approach allows scientists to quasi-interactively visualize large volume datasets on scalable high-resolution display arrays.
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Paper Nr: 12
Title:

Multi-Level Grid Strategies for Ray Tracing
Authors:

João M. Pereira, Vasco Costa, Vasco Costa and João M. Pereira
Abstract: Grids have some of the lowest ray tracing acceleration structure build times. This is because acceleration structure construction is analogous to a sorting algorithm. The ideal behavior for a sorting algorithm is to have O(N) time complexity regarding the number of elements. Grids also have O(N) construction time complexity regarding the number of primitives unlike other commonly used acceleration structures, such as kd-trees or bounding volume hierarchies, which have an O(N log N) lower bound. This trait makes grid ray tracing interesting for many applications including animation. Recent algorithmic developments have also made it possible to achieve one-level grid construction, with low memory requirements, by compressing empty grid cells. Unfortunately one-level grids achieve lower render time performance than recursive structures such as multi-level grids. We present a method for rapidly building a grid with similarly good render time performance and using less memory than classic multi-level grids. We demonstrate that this method is a remarkably effective solution for interactive ray tracing of large scanned models.
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Paper Nr: 22
Title:

An Empirical Evaluation of a GPU Radiosity Solver
Authors:

Günter Wallner
Abstract: This paper presents an empirical evaluation of a GPU radiosity solver which was described in the authors previous work. The implementation is evaluated in regard to rendering times in comparision with a classical CPU implementation. Results show that the GPU implementation outperforms the CPU algorithm in most cases, most importantly, in cases where the number of radiosity elements is high. Furthermore, the impact of the projection – which is used for determining the visibility – on the quality of the rendering is assessed. Results gained with a hemispherical projection performed in a vertex shader and with a real non-linear hemispherical projection are compared against the results of the hemicube method. Based on the results of the evaluation, possible improvements for further research are pointed out.
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Paper Nr: 30
Title:

A HYBRID APPROACH FOR HIGH QUALITY REAL-TIME TERRAIN RENDERING AND OPTIMIZED A-PRIORI ERROR ESTIMATION
Authors:

Falko Löffler, Sebastian Schwanke, Falko Löffler, Sebastian Schwanke and Heidrun Schumann
Abstract: This paper describes a hybrid approach for high-quality real-time terrain rendering. The contributions of the work are twofold. First, a novel parallel preprocessing scheme for necessary a-priori error-bounds calculation based on the widely applied longest-edge-bisection approach is proposed, which exploits current multi-core CPU architectures. Compared to the common recursive and thus computationally expensive procedure, a significant performance increase can be achieved. Second, a novel method for view-dependent terrain rendering is described which combines the advantages of triangle-based CPU and patch-optimized GPU algorithms. We exploit frame-to-frame coherence by caching refined geometry on local VRAM in combination with an optimized update process. In contrast to patch-based methods, a substantial reduction of the number of primitives and rendering time can be achieved.
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Paper Nr: 46
Title:

Interactive Design and Debugging of GPU-Based Volume Visualizations
Authors:

Jennis Meyer-Spradow, Jennis Meyer-Spradow, Timo Ropinski, Jörg Mensmann and Klaus Hinrichs
Abstract: There is a growing need for custom visualization applications to deal with the rising amounts of volume data to be analyzed in fields like medicine, seismology, and meteorology. Visual programming techniques have been used in visualization and other fields to analyze and visualize data in an intuitive manner. However, this additional step of abstraction often results in a performance penalty during the actual rendering. In order to prevent this impact, a careful modularization of the required processing steps is necessary, which provides flexibility and good performance at the same time. In this paper, we will describe the technical foundations as well as the possible applications of such a modularization for GPU-based volume raycasting, which can be considered the state-of-the-art technique for interactive volume rendering. Based on the proposed modularization on a functional level, we will show how to integrate GPU-based volume ray-casting in a visual programming environment in such a way that a high degree of flexibility is achieved without any performance impact.
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Paper Nr: 64
Title:

Embedding Hierachical Deformation within a realtime Scene Graph
Authors:

Martin Knuth, Arjan Kuijper and Jörn Kohlhammer
Abstract: Scene graphs are widely used as a description of spatial relations between objects in a scene. Current scene graphs use linear transformations for this purpose. This limits the relation of two objects in the hierarchy to simple transformations like sheer, translation, rotation and scaling. In contrast to this, we want to represent and control deformations that result from propagating the dynamics of objects to deformable attached objects. Our solution is to replace the linear 4x4 matrix-based transformation of a scene graph by a more generic trilinear transformation. The linear transformation allows the composition of the transformation hierarchy into one transformation. Our approach additionally allows the handling of deformations on the same level. Building on this concept we present a system capable of real-time rendering. The computations of the applied deformations of the scene graph are performed in real-time on the GPU. We allow the approximation of arbitrary nonlinear transformations and deformations by utilising grids of trilinear transformations in our system. As an application we show geometric attachments on deformable objects and their deformation on a scene graph level.
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Paper Nr: 67
Title:

VISUALIZATION BY EXAMPLE - A CONSTRUCTIVE VISUAL COMPONENT-BASED INTERFACE FOR DIRECT VOLUME RENDERING
Authors:

Bingchen Liu, Burkhard Wuensche and Timo Ropinski
Abstract: Direct Volume Rendering (DVR) is a popular technique for visualizing and exploring 3D data sets. The method visualizes data by associating it with colour and opacity values using the model of a light-emitting gas. The effectiveness of the resulting visualizations critically depends on finding transfer functions which emphasize structures in the underlying data. Various widgets have been proposed for creating complex transfer functions, but require users to have both a domain knowledge and a good understanding of the DVR concepts. In order to make DVR accessible to a wider range of users we need a more intuitive interface. In this paper we present a spreadsheet-like constructive visual component-based interface which allows novice user to efficiently find meaningful transfer functions. The interface uses a programming-by-example style approach and exploits the domain knowledge of the user without requiring an understanding of the DVR algorithm and the underlying physical and mathematical concepts. Our application automatically analysis histograms using a novel approach based on the Douglas-Peucker algorithm in order to identify potential structures in the data set. Sample visualizations of the resulting structures are presented to the user who can refine structures and combine them to more complex visualizations. We have integrated the interface into the Voreen volume rendering tool and used it to visualize volumetric data sets from different domains. Preliminary tests confirm that the interface is easy to use, and enables non-expert users to identify structures which they are unable to reveal using the traditional transfer function design interface.
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Paper Nr: 21
Title:

AUTOMATIC COMPUTER GENERATION OF STIPPLED ILLUSTRATIONS WITH COLOUR FELT-TIP PENS
Authors:

Germán Arroyo and Domingo Martin
Abstract: Nowadays, non-photorealistic rendering is an area that not only focuses on simulating what artists do or the tools they use, but also on generating new expressive tools for digital art. In this paper we present a new algorithm to generate beautiful stippling illustrations with colour felt-tipped pen from a photograph or an image. This technique is not currently used by artists due to technical limitations, and thus the algorithm may prove a useful addition to the tools used by an artist. We introduce a novel stochastic approach to place coloured dots in a specific order based on the information about the contrast, borders and the histogram of the input image. The system is able to generate an unlimited number of non regular synthetic coloured dots without the need for scanning. These dots will be composed in a specific order to generate the final illustration.
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Paper Nr: 54
Title:

A Compression Scheme for Efficient Remote Streaming of Dynamic 3D Content
Authors:

Paolo S. Gasparello, Giuseppe Marino, Paolo S. Gasparello, Davide Vercelli, Franco Tecchia and Massimo Bergamasco
Abstract: Real-time 3D content distribution over a network (either LAN or WAN) requires facing several challenges, most notably the handling of the large amount of data usually associated with 3D meshes. The scope of the present paper falls within the well-established context of real-time capture and streaming of OpenGL command sequences, focusing in particular on data compression schemes. However, we advance beyond the state-of-the-art improving over previous attempts of ``in-frame'' geometric compression on 3D structures inferred from generic OpenGL command sequences and adding ``inter-frame'' redundancy exploitation of the traffic generated by the typical architecture of interactive applications.
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Area 3 - Animation and Simulation

Full Papers
Paper Nr: 56
Title:

XFEM Framework for Cutting Soft Tissue
Authors:

Luis Gutiérrez and Félix F. Ramos-Corchado
Abstract: Currently, there are many approaches in computer graphics (CG) that deal with topological changes; some of these are non-interactive animations, unstable or not precise enough to medical applications. It has been found that the Extended Finite Element Method (XFEM) is stable, accurate, with excellent performance and suitable for virtual surgery in real time; nevertheless, to maintain the provided advantages, the selection and creation of a set of CG methods is required that fulfill the requirements of the XFEM. We propose an embedded mapping method that enables the relation of the XFEM elements, with the visual and collision meshes, making the user interaction more dynamic. Furthermore, based on this new mapping method an interactive cutting algorithm is suggested considering a geometric analysis. The XFEM, as a core of our framework, efficiently simulates the topological changes consequently, making the interaction in real time possible, which will allow the creation of more complex simulations of higher impact in the medical area.
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Paper Nr: 60
Title:

Change-Point Detection on the Lie Group SE(3) for Segmenting Gesture-Defined Spatial Rigid Motion
Authors:

Loic Merckel and Toyoaki Nishida
Abstract: Common CAD interfaces for editing spatial motion of virtual objects, which include both position and orientation information, are often hampered by complexity and lack of intuitiveness. As the demand for motion data is increasing, e.g., in computer graphics or mixed reality, the development of new interfaces that offer a natural means of specifying arbitrary motion becomes essential. A solution consists in relying on live motion capture systems to record user's gestures through space. In this context, we present a novel method for discovering change-points in a time series of elements in the set of rigid-body motion in space SE(3). The goal is to segment gesture-defined motion with in mind the development of a method for enhancing the user's intent. Although numerous change-points detection techniques are available for dealing with scalar, or vector, time series, the generalization of these techniques to more complex structures may require overcoming difficult challenges. The group SE(3) does not satisfy closure under linear combination. Consequently, most of the statistical properties, such as the mean, cannot be properly estimated in a straightforward manner. We present a method that takes advantage of the Lie group structure of SE(3) to adapt a difference of means method. Especially, we show that the change-points in SE(3) can be discovered in its Lie algebra se(3) that forms a vector space. The performance of our method is evaluated through both synthetic and real data.
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Paper Nr: 78
Title:

A Nonlinear Vertex-Based Model for Animation of Two-Dimensional Dry Foam
Authors:

Micky Kelager and Kenny Erleben
Abstract: Foam is the natural phenomenon of bubbles that arise due to nucleation of gas in liquids. The current state of art in Computer Graphics rarely includes foam effects on large scales. In this paper we introduce a vertex-based, quasi-static equilibrium model from the field of Computational Physics as a new paradigm for foam effects. Dynamic processes like gas diffusion and bubble collapse are added prior equilibration. Animation-wise the numerical model is well behaved and stable and can converge even if the foam is locally ill-defined. A novel contribution is the Ghost-Bubble method that allows foam simulations with free dynamic boundary conditions. The presented model is interesting and well suited for 2D graphics applications like video games and procedural or animated textures.
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Short Papers
Paper Nr: 3
Title:

MODELING AND TRANSFORMATION OF 3D HUMAN MOTION
Authors:

Seyed A. Etemad and Ali Arya
Abstract: Applying different styles of motion such as those related to gender, age and energy of the performer, are important themes in creating realistic animation. While typically different sets of motion sequences must be created for different styles, in this paper we present a technique for transferring motion styles across different sequences. This allows transforming the style of a motion while preserving the primary action class of the original motion. A mathematical model capable of defining both the action class and the style class is proposed and based on the model, the conversion data are computed. A series of piece-wise time warping procedures are conducted prior to employing the defined transformation function. Using this technique, there would be no need for a new set of motion data to be captured or keyframed as the original motion data can be altered to show the desired style.
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Paper Nr: 36
Title:

Tessellating ocean surfaces
Authors:

Anna Puig-Centelles, Francisco Ramos, Miguel Chover, Oscar Ripolles and Mateu Sbert
Abstract: Modeling and rendering realistic ocean scenes has been thoroughly investigated for many years. Its appearance has been studied and it is possible to find very detailed simulations with a high degree of realism. Nevertheless, real-time management of the huge heightmaps that are necessary for rendering ocean is still not solved. We propose a new technique for tessellating the ocean surface on GPU. This technique is capable of offering view-dependent approximations of the mesh while maintaining coherence among the extracted approximations when refining or coarsening the mesh. This feature is very important as most solutions previously presented must re-tessellate from the initial mesh. This tessellation algorithm is combined with Perlin noise, reflection and the fresnel term to offer realistic visualizations.
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Paper Nr: 84
Title:

Real Time Forest Fire Simulation with Extinguishment Support
Authors:

Anis Korchi, Aitor Moreno and Álvaro Segura
Abstract: Fires and other related disasters provoke great destruction of high valuable environments and economical losses. In this work, we present a forest fire spreading algorithm to be used in real time and interactive Virtual Simulations. The main objective is to obtain a fast, interactive and quasi-realistic Virtual Simulation to be used in the simulation of virtual scenarios where fire-fighters and controllers will be trained. The algorithm supports the main variables involved in the fire spreading (slope and wind) and the radiation effect makes the forest fires bypass rivers or firewalls. To complete the simulation, a basic model has been added to extinguish the fire using water.
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Area 4 - Interactive Environments

Full Papers
Paper Nr: 14
Title:

Designing a Mixed Reality Framework for Enriching Interactions in Robot Simulation
Authors:

Ian Y. Chen, Bruce MacDonald and Burkhard Wuensche
Abstract: Experimentation of expensive robot systems typically requires complex simulation models and expensive hardware setups for constructing close-to-real world environments in order to obtain reliable results and draw insights to the actual operation. However, the test-development cycle is often time-consuming and resource demanding. A cost-effective solution is to conduct experiments by replacing expensive or dangerous components with simulated counterparts. Based on the concept of Mixed Reality (MR), robot simulation systems can be created to involve real and virtual entities in the simulation loop. However, seamless interaction between objects from the real and the virtual world remains a challenge. This paper presents a generic framework for constructing MR environments that facilitate interactions between objects from different dimensions of reality. In comparison to previous frameworks, we propose a new interaction scheme that describes the necessary stages for creating interactions between real and virtual objects. We demonstrate the strength of our MR framework and the proposed MR interaction scheme in the context of robot simulation.
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Short Papers
Paper Nr: 23
Title:

INVESTIGATING THE INFLUENCE OF COMMUNICATION AND INPUT DEVICES ON COLLABORATION IN VIRTUAL ENVIRONMENTS
Authors:

Anastasiia Beznosyk, Chris Raymaekers, Karin Coninx, Peter Quax and Wim Lamotte
Abstract: As collaborative virtual environments (CVEs) are becoming more popular for both entertainment and professional activities, it is important to know which factors influence the collaboration between participants. This paper investigates two aspects of interaction in the context of collaboration between two users. A puzzlesolving task in a basic interactive virtual environment was used as a case study. The influence of voice communication was assessed in a user experiment. Furthermore, as different I/O devices can be used with this kind of applications, the fact whether both participants are using the same device or not, was also checked. From this study, we can conclude that the inclusion of voice communication is important when working on the same task in a CVE, since this allows the participants to explicitly divide the work. On the other hand, the usage of the same kind of device by both users does not significantly influence the collaboration. The availability of different devices shows not to be a problem for the acceptance of CVEs, and therefore it is not necessary to impose a certain device, which is obviously preferable, especially when dealing with home users.
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Paper Nr: 32
Title:

HANIME An H-Anim Compliant Avatar Editor for NVEs
Authors:

Christos Bouras, Kostas Kartsakalis, Vassilis Triglianos and Th. Tsiatsos
Abstract: This paper addresses the problem of a visual H-Anim avatar editor. Although H-Anim is a very promising standard for interchangeable avatars and avatar’s animation, the lack of an effective yet simple to use visual avatar editor could repel users from H-Anim compliant Networked Virtual Environments. Therefore this paper presents an H-Anim compliant editor, called HanimE, for creating avatars for Networked Virtual Environments. This editor is entirely based on a graphical user interface and allows users to customize H-Anim avatars, in a simple yet effective manner. The avatars created by HanimE can be integrated in various H-Anim compliant Networked Virtual Environments regardless of the technology they are built on, since they are X3D files.
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Paper Nr: 44
Title:

Combining Absolute Positioning and Vision for Wide Area Augmented Reality
Authors:

Andrew Calway and Tom Banwell
Abstract: One of the major limitations of vision based mapping and localisation is its inability to scale and operate over wide areas. This restricts its use in applications such as Augmented Reality. In this paper we demonstrate that the integration of a second absolute positioning sensor addresses this problem, allowing independent local maps to be combined within a global coordinate frame. This is achieved by aligning trajectories from the two sensors which enables estimation of the relative position, orientation and scale of each local map. The second sensor also provides the additional benefit of reducing the search space required for efficient relocalisation. Results illustrate the method working for an indoor environment using an ultrasound position sensor, building and combining a large number of local maps and successfully relocalising as users move arbitrarily within the map. To show the generality of the proposed method we also demonstrate the system building and aligning local maps in an outdoor environment using GPS as the position sensor.
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Paper Nr: 61
Title:

Using PhysX for Simulation-based Endoscopic Hardware Design
Authors:

Felix Dingeldey, Karsten Isakovic and Ilja Teiche
Abstract: Computer-assistance becomes increasingly important in minimally invasive surgery. Automation and image-processing techniques are employed for assisting surgeons with their highly skilled tasks. Our research is aimed at developing a novel system for laparoscopic surgery consisting of a new type of endoscope and augmented reality components. In order to facilitate the design of the hardware and the algorithms, we developed a virtual endoscopy simulator. It utilizes the capabilities of NVIDIA's physics engine "PhysX" for simulating the physical behavior of soft tissue, instruments, and smoke. In this paper, we present our proposed solutions for modeling the objects using PhysX and discuss possible problems specific to the domain of medical simulation.
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Paper Nr: 62
Title:

Mixing Virtual Reality and 2D Visualization - Using Virtual Environments as Visual 3D Information Systems for Discussion of Data from Geo- and Environmental Sciences
Authors:

Bjoern Zehner
Abstract: 3D stereoscopic visualization and virtual reality techniques are increasingly used for quality control, analysis and discussion of 3D geoscientific data in the oil and gas industry. They provide an excellent and easily comprehensible insight into complex 3D structures of the earth's subsurface. However, in many research topics in environmental and geosciences the analysis of data usually also involves data that might be better viewed in 2D. Examples are maps or histograms. The use of virtual environments as visual information systems for the efficient communication and discussion of complex multi-attribute data sets also requires 2D data to be visualized with a high quality. Further it is often not possible to show all the relevant information simultaneously and so an interactive virtual environment is required that provides an overview and the necessary interaction techniques to select additional information, e.g. from a database, to be visualized on request. This article describes the hardware setup installed at the UFZ Centre for Environmental Research and a software solution for how to use this setup efficiently to connect 2D data representations with 3D visualization and interaction.
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Paper Nr: 69
Title:

Real-Time Interactive L-system: An Interactive Plant And Fractal Generator
Authors:

Ludovic Hamon, Paul Richard, Emmmanuelle Richard and Jean-Louis Ferrier
Abstract: L-system is a rewriting process based on Chomsky grammar that can generate 3D fractals and virtual plants. Its efficiency has been proved for more than twenty years with the works of Lindenmayer and Prusinkiewicz in particular. This paper presents a Real-Time Interactive L-system (RTIL-system) allowing real-time rendering, interactions with a user and/or the environment, haptic feedback and covering most of the important L-systems extensions such as parametric and context sensitive features. Different potentialities of the RTIL-system are illustrated where the user intervention becomes an essential element of plant/fractal evolution through Virtual Reality and Augmented Reality applications.
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Paper Nr: 82
Title:

A VIRTUAL KITCHEN TO ASSESS THE ACTIVITIES OF DAILY LIFE IN ALZHEIMER'S DISEASE
Authors:

Paul Richard, Emmmanuelle Richard, Philippe Allain, Didier L. Gall, Jeremy Besnard and Lisa Massenot
Abstract: This paper presents the EVACOG project that aims to investigate the usefulness of Virtual Environments (VEs) in cognitive assessment. Our objective is to evaluate the cognitive and/or behavioral abilities of patients with brain lesions in scenarios implying the planning and the execution of everyday tasks such as driving a car or preparing a cup of coffee. In this paper we describe a simple and effective VE (a kitchen) designed to assess patient’s ability to prepare a cup of coffee. We focus on the assessment results obtained with eight patients with Alzheimer’s disease which were compared to healthy elderly subjects. Participants were instructed to prepare a cup of coffee in the virtual kitchen. Results revealed significant impairments in patients with Alzheimer’s disease. Results of this study support the use the virtual kitchen to assess everyday life activities among persons with Alzheimer’s disease
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Paper Nr: 86
Title:

INTERACTIVE CONFIGURATION OF RESTRICTED SPACES USING VIRTUAL REALITY AND CONSTRAINT PROGRAMMING TECHNIQUES
Authors:

Paul Richard, Marouene Kefi and Vincent Barichard
Abstract: In this paper, we describe innovative approaches for the design of intelligent virtual environments (VE) for interactive problem solving. Thus, we propose to extend VEs to support constraint-based interaction through the use of Constraint Programming (CP) techniques. The aim of this paper is to argue for the need of CP integration in VEs and its high relevance in the 3D-objects layout problem. The user manipulation will be translated as incoming queries of the intelligent module (solver) which will generate a solution compatible with the design requirements. Thus, the task of the solver is to satisfy the constraints specified by the system in response to user interaction. In order to exhibit a high degree of visual richness and realism, the use of human-scale multi-modal 3D interaction techniques and tools is proposed.
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Paper Nr: 31
Title:

3D INTERACTION ORIENTED OBJECT MODEL
Authors:

Cheng Cheng
Abstract: Human computer interaction (HCI) is the most urgent challenge to virtual environment based manufacturing today. Traditionally VRML/X3D standards are used as the main object models of virtual environment (VE), and collision detection serves as the exclusive perception mechanism in such a environment. It is observed that these models are difficult to satisfy the requirement of 3D human computer interaction. This paper tries to provide a new object model scheme for virtual assembly, which is a typical virtual environment application that has the most critical HCI requirements. The work of this paper includes introduction of object scheme, formalization of object construction, new perception mechanism, and object behaviour abstraction and validation. The provided object model is applied and validated in virtual assembly prototype system.
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