GRAPP 2009 Abstracts


Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 31
Title:

FAST SPATIALLY CONTROLLABLE 2D/3D TEXTURE SYNTHESIS AND MORPHING FOR MULTIPLE INPUT TEXTURES

Authors:

Felix Manke and Burkhard Wünsche

Abstract: Texture synthesis and morphing are important techniques for efficiently creating realistic textures used in scientific and entertainment applications. In this paper we present a novel fast algorithm for multi-dimensional texture synthesis and morphing that is especially suitable for parallel architectures such as GPUs or direct volume rendering (DVR) hardware. Our proposed solution generalizes the synthesis process to support higher than three-dimensional synthesis and morphing. We introduce several improvements to previous 2D synthesis algorithms, such as new appearance space attributes and an improved jitter function. We then modify the synthesis algorithm to use it for texture morphing which can be applied to arbitrary many 2D input textures and can be spatially controlled using weight maps. Our results suggest that the algorithm produces higher quality textures than alternative algorithms with similar speed. Compared to higher quality texture synthesis algorithms, our solution is considerablly faster and allows the synthesis of additional channels without affecting the running time of the synthesis at all. The method is easily extended to allow fast 3D synthesis and as another novel contribution we show several examples for morphed solid 3D textures. Overall the presented technique provides an excellent trade-off between speed and quality, is highly flexible, allows the use of arbitrary channels such as transparencies and displacement maps, can be extended to arbitrary dimensions and is suitable for a GPU-implementation.

Paper Nr: 33
Title:

FACIAL NORMAL MAP CAPTURE USING FOUR LIGHTS - An Effective and Inexpensive Method of Capturing the Fine Scale Detail of Human Faces using Four Point Lights

Authors:

Jasenko Zivanov, Pascal Paysan and Thomas Vetter

Abstract: Obtaining photorealistic scans of human faces is both challenging and expensive. Capturing the highfrequency components of skin surface structure requires the face to be scanned at very high resolutions, outside the range of most structured light 3D scanners. We present a novel and simple enhancement to the acquisition process, requiring only four photographic flashlights and three texture cameras attached to the structured light scanner setup. The three texture cameras capture one texture map (luminance map) of the face as illuminated by each of the four flash-lights. Based on those four luminance textures, three normal maps of the head are approximated, one for each color channel. Those normal maps are then used to reconstruct a 3D model of the head at a much higher mesh resolution, in order to validate the normals. Finally, the validated normals are used as a normal map at rendering time. Alternatively, the reconstructed high resolution model can also be used for rendering.

Paper Nr: 48
Title:

ADAPTATIVE CUBICAL GRID FOR ISOSURFACE EXTRACTION

Authors:

John Congote, Aitor Moreno, Iñigo Barandiaran, Javier Barandiaran and Oscar E. Ruiz

Abstract: This work proposes a variation on the Marching Cubes algorithm, where the goal is to represent implicit functions with higher resolution and better graphical quality using the same grid size. The proposed algorithm displaces the vertices of the cubes iteratively until the stop condition is achieved. After each iteration, the difference between the implicit and the explicit representations are reduced, and when the algorithm finishes, the implicit surface representation using the modified cubical grid is more detailed, as the results shall confirm. The proposed algorithm corrects some topological problems that may appear in the discretisation process using the original grid.

Paper Nr: 52
Title:

MODELING AND RENDERING THE GROWTH OF SPELEOTHEMS IN REAL-TIME

Authors:

Daniel Menin Tortelli and Marcelo Walter

Abstract: Among the many natural phenomena already studied in computer graphics research, the interior of caves remains largely unexplored. We present in this paper a plausible approach, based on Geological studies, for modeling the genesis and growth of speleothems. Speleothems are mineral depositions formed in caves, such as stalactites, stalagmites and columns. Our approach takes advantage of the new geometry shader, present in the new generation of GPUs, and can generate in a controlled way, a large variety of cave scenes, with meaningful geological parameters.

Short Papers
Paper Nr: 7
Title:

SYMMETRY-BASED COMPLETION

Authors:

Thiago Pereira, Renato Paes Leme, Luiz Velho and Thomas Lewiner

Abstract: Acquired images often present missing, degraded or occluded parts. Inpainting techniques try to infer lacking information, usually from valid information nearby. This work introduces a new method to complete missing parts from an image using structural information of the image. Since natural and human-made objects present several symmetries, the image structure is described in terms of axial symmetries, and extrapolating the symmetries of the valid parts completes the missing ones. In particular, this allows inferring both the edges and the textures.

Paper Nr: 15
Title:

IMPROVING 3D SHAPE RETRIEVAL WITH SVM

Authors:

Elisabetta Delponte, Curzio Basso, Francesca Odone and Enrico Puppo

Abstract: In this paper we propose a technique that combines a classification method from the statistical learning literature with a conventional approach to shape retrieval. The idea that we pursue is to improve both results and performance by filtering the database of shapes before retrieval with a shape classifier, which allows us to keep only the shapes belonging to the classes most similar to the query shape. The experimental analysis that we report shows that our approach improves the computational cost in the average case, and leads to better results.

Paper Nr: 16
Title:

AUTOMATIC TRIMAP EXTRACTION FOR EFFICIENT ALPHA MATTING BASED ON GRADIENT FIELD TRANSFORMS

Authors:

Sang Min Yoon and Holger Graf

Abstract: Image/Video Matting aims at solving the problem of accurate foreground estimation from a given background within still images or video sequences. The standard alpha matting method starts from a trimap, which separates an input image into three regions: definitely foreground, definitely background, and unknown regions. This paper presents an automatic trimap extraction based on an affine transformation of gradient fields in order to achieve an improved and robust Image/Video matting method. A gradient field based background and foreground segmentation technique provides a trimap extraction, which is robust to changing light conditions within semi-transparent objects. Our proposed background subtraction is based on affine transformed gradient projections of the input and background image and removes the background texture from a given image, preserving the texture of the foreground objects. The presented automatic trimap extraction method reduces the manual labor work in extracting and embedding target objects into a new background image or video sequences and might find its application within the broadcasting or movie industry.

Paper Nr: 18
Title:

A VECTORIZED TRAVERSAL ALGORITHM FOR RAY TRACING

Authors:

José María Noguera, Carlos Ureña and Rubén Jesús García

Abstract: This article presents an optimized ray tracing algorithm which improves standard existing algorithms by processing simultaneously a large set of rays and carrying out a single traversal of the spatial indexing of the scene with all rays. This allows hardware SIMD functionality to be used efficiently and produces coherent memory accesses. Furthermore, during the single traversal, rays are grouped in such a way that these advantages are maintained for non coherent ray sets. The algorithm was observed to reduce the computation costs with respect to other standard solutions, especially for non coherent ray sets. It is worth noting that its characteristics make it especially suitable for graphics hardware.

Paper Nr: 20
Title:

HYBRID TERRAIN VISUALIZATION BASED ON LOCAL TESSELLATIONS

Authors:

E. G. Paredes, C. Lema, M. Amor and M. Bóo

Abstract: Hybrid terrain models represent an effective approach to combine geographic data with different acquisition properties. Terrain models constituted by regular grid elevation data may locally integrate detailed TIN meshes to represent morphologically complex terrain features and artificial objects. However, direct rendering of hybrid terrain models poses additional difficulties: holes and geometric discontinuities between the borders of the different parts would appear in the images. In this paper we present two new software based proposals for efficient hybrid terrain visualization. Both proposals generate high-quality geometrically continuous models and support multiresolution methods over regular grids.

Paper Nr: 23
Title:

INTERPOLATORY ADAPTIVE SUBDIVISION FOR MESH LOD EDITING

Authors:

Daniele Panozzo and Enrico Puppo

Abstract: We propose an adaptive interpolatory scheme for subdivided triangle meshes that is compliant with the modified butterfly subdivision and can be used effectively and efficiently in selective editing of meshes. Our scheme is developed upon the RGB subdivision, an adaptive scheme that is based on the factorization of the one-to-four triangle split pattern. We introduce the concept of topological angle and related operators to efficiently navigate and edit an adaptively subdivided mesh. On the basis of this new scheme, we present an interactive application that allows a user to freely edit the Level of Detail of a model starting at a base mesh.

Paper Nr: 47
Title:

GENERATING 3D PLANTS USING LINDENMAYER SYSTEM

Authors:

Kamil Ciosek and Pawel Kotowski

Abstract: The main focus of this paper is the analysis of modern methods of algorithmic plant generation. First, a brief introduction is given to the necessary formalism: Lindenmayer system. It is followed by a description of each stage of plant generation process. These include algorithms for obtaining: leaf venation graph, leaf texture, stem texture, and the geometry and topology of the whole plant. In particular, the following approaches have been used: textures are obtained from transformed noise, a general plant description is generated with a parametric Lindenmayer system and a purpose-built particle-based algorithm is used to simulate leaf venation. The last section gives a detailed description of four sample systems used to generate different plants, outlining the reasons why a given system gives the desired graphical result.

Paper Nr: 55
Title:

TESSELLATING ALGEBRAIC CURVES AND SURFACES USING A-PATCHES

Authors:

Curtis Luk and Stephen Mann

Abstract: This work approaches the problem of triangulating algebraic curves and surfaces with a subdivision-style algorithm using A-patches. An algebraic curve or surface is converted from the monomial basis to the Bernstein-Bezier basis over a simplex. If the coefficients are all positive or all negative, then the curve or surface does not pass through the domain simplex. If the scalar Bernstein coefficients are of mixed sign and have a layer separating the positive from the negative, then the patch is in A-patch format and can be efficiently tessellated. Cases of mixed sign without a separating layer are resolved by subdividing the structure into a set of smaller patches and repeating the algorithm. Using A-patches to generate a tessellation of the surface has the advantage of reducing the amount of subdivision required. And because of the A-patch properties, we are guaranteed that features within the designated region will not be missed.

Paper Nr: 65
Title:

A NEW POTENTIAL FUNCTION FOR SELF INTERSECTING GIELIS CURVES WITH RATIONAL SYMMETRIES

Authors:

Yohan D. Fougerolle, Frédéric Truchetet and Johan Gielis

Abstract: We present a new potential field equation for self-intersecting Gielis curves with rational rotational symmetries. In the literature, potential field equations for these curves, and their extensions to surfaces, impose the rotational symmetries to be integers in order to guarantee the unicity of the intersection between the curve/surface and any ray starting from its center. Although the representation with natural symmetries has been applied to mechanical parts modeling and reconstruction, the lack of a potential function for Rational symmetry Gielis Curves (RGC) remains a major problem for natural object representation, such as flowers and phyllotaxis. We overcome this problem by combining the potential values associated with the multiple intersections using R-functions. With this technique, several differentiable potential fields can be defined for RGCs. Especially, by performing N-ary R-conjunction or R-disjunction, two specific potential fields can be generated: one corresponding to the inner curve, that is the curve inscribed within the whole curve, and the outer -or envelope- that is the curve from which self intersections have been removed.

Posters
Paper Nr: 58
Title:

COMPARING GNG3D AND QUADRIC ERROR METRICS METHODS TO SIMPLIFY 3D MESHES

Authors:

Rafael Álvarez, Leandro Tortosa, José F. Vicent and Antonio Zamora

Abstract: The primary objective of this paper is to carry out a performance comparison of two models to generate simplified meshes representing 3D objects, the GNG3D model and the Quadric Error Metrics (QEM) model. The QEM model constitutes a well-known classical algorithm based on interactive contraction of vertex pairs and represents perhaps the best balance yet between speed, fidelity, and robustness of the proposed models and algorithms for mesh simplification in the last years. The GNG3D model is based on a neural network algorithm and a reconstruction phase of the object. For the purpose of comparison, several error measurements are proposed and motivated in order to evaluate the quality of the approximations that both models produce. It is justified with numerical results that the GNG3D model exhibits better performance for several 3D objects with different topologies and geometric properties.

Paper Nr: 68
Title:

IMPLEMENTATION OF 24-ARY GRID REPRESENTATION FOR RECTANGULAR SOLID DISSECTIONS

Authors:

Tomokazu Arita, Satoshi Kishira, Tomoe Motohashi, Kenshi Nomaki, Kimio Sugita, Kensei Tsuchida and Takeo Yaku

Abstract: In this paper, we propose 24-ary grid graphs corresponding to rectangular solid dissections for ruled line preserving operations. We also show a data structure called H9CODE that corresponds to the 24-ary grid graphs. Furthermore, we describe a voxel unification method in the 24-ary grid graphs and show that the 24-ary grid graphs are an effective model to represent solid graphics.

Area 2 - Rendering

Full Papers
Paper Nr: 8
Title:

3D VISUALIZATION AND SEGMENTATION OF BRAIN MRI DATA

Authors:

Konstantin Levinski, Alexei Sourin and Vitali Zagorodnov

Abstract: Automatic segmentation of brain MRI data usually leaves some segmentation errors behind that are to be subsequently removed interactively using computer graphics tools. This interactive removal is normally performed by operating on individual 2D slices. It is very tedious and still leaves some segmentation errors which are not visible on the slices. We have proposed to perform a novel 3D interactive correction of brain segmentation errors introduced by the fully automatic segmentation algorithms. We have developed the tool which is based on a 3D semi-automatic propagation algorithm. The paper describes the implementation principles of the proposed tool and illustrates its application.

Paper Nr: 41
Title:

NEW ALGORITHMS FOR GPU STREAM COMPACTION - A Comparative Study

Authors:

Pedro Miguel Moreira, Luís Paulo Reis and A. Augusto de Sousa

Abstract: With the advent of GPU programmability, many applications have transferred computational intensive tasks into it. Some of them compute intermediate data comprised by a mixture of relevant and irrelevant elements in respect to further processing tasks. Hence, the ability to discard irrelevant data and preserve the relevant portion is a desired feature, with benefits on further computational effort, memory and communication bandwidth. Parallel stream compaction is an operation that, given a discriminator, is able to output the valid elements discarding the rest. In this paper we contribute two original algorithms for parallel stream compaction on the GPU. We tested and compared our proposals with state-of-art algorithms against different data-sets. Results demonstrate that our proposals can outperform prior algorithms. Result analysis also demonstrate that there is not a best algorithm for all data distributions and that such optimal setting is difficult to be achieved without prior knowledge of the data characteristics.

Paper Nr: 44
Title:

AN INVERSE PROBLEM APPROACH TO BRDF MODELING

Authors:

Kei Iwasaki, Yoshinori Dobashi, Fujiichi Yoshimoto and Tomoyuki Nishita

Abstract: This paper presents a BRDF modeling method, based on an inverse problem approach. Our method calculates BRDFs to match the appearance of the object specified by the user. By representing BRDFs by a linear combination of basis functions, outgoing radiances of the object surface can be represented using basis functions. The calculation of the desired BRDF results from calculating the corresponding coefficients of basis functions that minimize the sum of differences between the outgoing radiances, represented using basis functions and user specified radiances. The properties that BRDFs must satisfy are described by linear constraint conditions. This minimization problem can be solved, interactively, using a linearly constrained least squares approach. Thus, our method allows the user to design BRDFs directly, under fixed complex lighting and viewpoint, and to view the rendering results interactively, under dynamic lighting and viewpoint.

Paper Nr: 45
Title:

JUMPING JACK - A Parallel Algorithm for Non-Monotonic Stream Compaction

Authors:

Pedro Miguel Moreira, Luís Paulo Reis and A. Augusto de Sousa

Abstract: Stream Compaction is an important task to perform in the context of data parallel computing, useful for many applications in Computer Graphics as well as for general purpose computation on graphics hardware. Given a data stream containing irrelevant elements, stream compaction outputs a stream comprised by the relevant elements, discarding the rest. The compaction mechanism has the potential to enable savings on further processing, memory storage and communication bandwidth. Traditionally, stream compaction is defined as a monotonic (or stable) operation in the sense that it preserves the relative order of the data. This is not a full requirement for many applications, therefore we distinguish between monotonic and non-monotonic algorithms. The latter motivated us to introduce the Jumping Jack algorithm as a new algorithm for nonmonotonic compaction. In this paper, experimental results are presented and discussed showing that, although simple, the algorithm has interesting properties that enable it to perform faster than existent state-of-the-art algorithms, in many circumstances.

Paper Nr: 49
Title:

REAL-TIME PIECEWISE PERSPECTIVE PROJECTIONS

Authors:

Haik Lorenz and Jürgen Döllner

Abstract: This paper presents an approach to real-time rendering of non-planar projections with a single center and straight projection rays. Its goal is to provide optimal and consistent image quality. It operates entirely in object space to remove the need for image resampling. In contrast to most other object-space approaches, it does not evaluate non-linear functions on the GPU, but approximates the projection itself by a set of perspective projection pieces. Within each piece, graphics hardware can provide optimal image quality. The result is a coherent and crisp rendering. Procedural textures and stylization effects greatly benefit from our method as they usually rely on screen-space operations. The real-time implementation runs entirely on GPU. It replicates input primitives on demand and renders them into all relevant projection pieces. The method is independent of the input mesh density and is not restricted to static meshes. Thus, it is well suited for interactive applications. We demonstrate it for an analytic and a freely designed projection.

Paper Nr: 70
Title:

SPARE TIME ACTIVITY SHEETS FROM PHOTO ALBUMS

Authors:

Gabriela Csurka and Marco Bressan

Abstract: We present a technique to generate some popular activity sheets from arbitrary images, in particular user photographs. We focus on activity sheets that are closely linked to coloring and shape completion. We first introduce a baseline approach based on color regions that works well for cartoon-like images and uncluttered hotographs. In more complex scenes, we show how this approach can be integrated with global textural cues for increasing the level of details that can convey semantic information. A final local stage takes advantage of object recognition and scene classification techniques for selective detailing in the foreground background regions. Though the resulting approach can be deployed in a fully automatic fashion, interactivity can be a desirable feature since it allows to account for errors and, more important, increase the level of personalization. We propose three levels of interactivity, depending on the user skills. For all steps of our system and addressed activity sheets we show representative results.

Paper Nr: 75
Title:

PARALLEL IMPLEMENTATION OF A GLOBAL LINE MONTE CARLO RADIOSITY

Authors:

Roel Martínez, Adrià Forés and Ignacio Martín

Abstract: Radiosity methods are known by their expensive computational cost. To compute high quality images with a lot of polygons or patches may take hours. For this reason parallel processing will be a good option in order to decrease the computational cost. On the other hand, Monte Carlo methods offer good alternatives for parallelization, given their intrinsic decomposition properties in independent subtasks. We have implemented our multipath method for radiosity using a cluster of PCs. Results are presented for 1 to 8 processors, exhibiting a good efficiency and scalability.

Short Papers
Paper Nr: 21
Title:

CACHED MULTI-BOUNCE SOLUTION AND RECONSTRUCTION FOR VOXEL-BASED GLOBAL ILLUMINATION

Authors:

Łukasz Piwowar and Rémy Malgouyres

Abstract: We address the main shortcomings of the voxel-based multi-bounce global illumination method of Chatelier and Malgouyres (2006), by introducing an iterated cached method which allows increasing sampling coarseness at each bounce for improved efficiency, and by introducing a ray-tracing based reconstruction process for a better final image quality. The result is a competitive accurate multi-bounce global illumination method with octree voxel-based irradiance caching.

Paper Nr: 29
Title:

THE PULL-PUSH ALGORITHM REVISITED - Improvements, Computation of Point Densities, and GPU Implementation

Authors:

Martin Kraus

Abstract: The pull-push algorithm is a well-known and very efficient pyramid algorithm for the interpolation of scattered data with many applications in computer graphics. However, the original algorithm is not very well suited for an implementation on GPUs (graphics processing units). In this work, several improvements of the algorithm are presented to overcome this limitation, and important details of the algorithm are clarified, in particular the importance of the correct normalization of the employed filters. Moreover, we present an extension for a very efficient estimate of the local density of sample points.

Paper Nr: 30
Title:

TEXTURE-ENHANCED DIRECT VOLUME RENDERING

Authors:

Felix Manke and Burkhard Wünsche

Abstract: Direct volume rendering (DVR) is a flexible technique for visualizing and exploring scientific and biomedical volumetric data sets. Transfer functions associate field values with colors and opacities, however, for complex data are often not sufficient for encoding all relevant information. We introduce a novel visualization technique termed texture-enhanced DVR to visualize supplementary data such as material properties and additional data fields. Smooth transitions in the underlying data are represented by coherently morphing textures within user defined regions of interest. The framework seamlessly integrates into the conventional DVR process, can be executed on the GPU, is extremely powerful and flexible, and enables entirely novel visualizations.

Paper Nr: 46
Title:

MULTI-PERSPECTIVE PANORAMAS OF URBAN SCENES WITHOUT SAMPLING ERRORS

Authors:

Siyuan Fang and Neill Campbell

Abstract: In this paper we introduce a framework for producing multi-perspective panoramas of urban streets from a dense collection of photographs. The estimated depth information are used to remove sampling errors caused by depth parallax of non-planar scenes. Then, different projections are automatically combined to create the multi-perspective panorama with minimal aspect ratio distortions, which is achieved by a two-phase optimization: firstly, the global optimal configuration of projections is computed and then a local adjustment is applied to eliminate visual artifacts caused by undesirable perspectives.

Paper Nr: 56
Title:

INTERACTIVE STEREO RENDERING FOR NON-PLANAR PROJECTIONS OF 3D VIRTUAL ENVIRONMENTS - With a Comparison of Image- and Geometry-based Approaches

Authors:

Matthias Trapp, Haik Lorenz and Jürgen Döllner

Abstract: Stereo rendering, as an additional visual cue for humans, is an important method to increase the immersion into 3D virtual environments. Stereo pairs synthesized for the left and right eye are displayed in a way that the human visual system interprets as 3D perception. Stereoscopy is an emerging field in cinematography and gaming. While generating stereo images is well known for standard projections, the implementation of stereoscopic viewing for interactive non-planar single-center projections, such as cylindrical and spherical projections, is still a challenge. This paper presents the results of adapting an existing image-based approach for generating interactive stereoscopic non-planar projections for polygonal scenes on consumer graphics hardware. In particular, it introduces a rendering technique for generating image-based, non-planar stereo pairs within a single rendering pass. Further, this paper presents a comparison between the image-based and a geometry-based approach with respect to selected criteria.

Paper Nr: 63
Title:

BLOCK AND QUADTREE BASED SIMPLIFICATION IN TILED BLOCKS TERRAIN ALGORITHMS

Authors:

Ivo Leitão and Beatriz Carmo

Abstract: With the advent of modern graphic processors, rendering a complex terrain in real time was suddenly possible. However the constant struggle between rendering quality and real time performance is still demanding more that we can actually get. Terrains are a prime example of that, the sheer amount of geometry and the constant need to achieve higher standards in image quality are always taking the graphical processors to their limits. Level of detail techniques, are therefore very important in this area and were used in multiple algorithms through the years. Tiled blocks are a category of terrain algorithms where the terrain is partitioned into square patches that are tessellated at different resolutions. This paper describes and compares two of the most common approaches used in the simplification process: block based simplification, where the simplification is local to the block, and quadtree based simplification, which uses the spatial partitioning principle of the quadtree to perform the simplification.

Paper Nr: 89
Title:

PYRAMIDAL MULTI-VIEW PBR - A Point-based Algorithm for Multi-view Multi-resolution Rendering of Large Data Sets from Range Images

Authors:

Sajid Farooq and J. Paul Siebert

Abstract: This paper describes a new Point-Based-Rendering technique that is parsimonious with the typically large data-sets captured by stereo-based, multi-view, 3D imaging devices for clinical purposes. Our approach is based on image pyramids and exploits the implicit topology relations found in range images, but not in unstructured 3D point-could representations. An overview of our proposed PBR-based system for visualisation, manipulation, integration and analysis of sets of range images at native resolution is presented along with initial multi-view rendering results.

Posters
Paper Nr: 43
Title:

GPU-BASED VOLUME RAY-CASTING SUPPORTING SPECULAR REFLECTION AND REFRACTION

Authors:

Timo Ropinski, Klaus Hinrichs and Jens Kasten

Abstract: Nowadays mostly local illumination models are used when rendering volumetric data. When computing global light effects, interactive frame rates are usually hard to achieve. We present an extension of GPU-based volume ray-casting, which allows to compute specular reflection and refraction effects at interactive frame rates on current commodity graphics hardware. In contrast to other techniques proposed for integrating these effects into volume rendering, our technique does not constrain the type of rendering used, i. e., it can be used with DVR as well as isosurface rendering.

Paper Nr: 79
Title:

REMOTE RENDERING OF LARGE BIOLOGICAL DATASETS

Authors:

Wolfram Schoor, Rüdiger Mecke, Udo Seiffert, Felix Bollenbeck and Uwe Scholz

Abstract: This paper presents remote rendering technologies to support the analysis and information exploration of large biological datasets. Reconstructed three-dimensional models and other data domains stored in a database are the foundation for the visualization. Remote Rendering via a clients web interface enables a widespread access to the data with interactive frame rates and high-quality rendering results without the demand of new client hardware. Moreover, the rendering server has the capability to manage multiple independent or collaborative sessions and has a very small bandwidth consumption over time.

Area 3 - Animation and Simulation

Full Papers
Paper Nr: 9
Title:

THE MASKLE: AUTOMATIC WEIGHTING FOR FACIAL ANIMATION - An Automated Approach the Problem of Facial Weighting for Animation

Authors:

Alun Evans, Marco Romeo, Marcelo Dematei and Josep Blat

Abstract: Facial animation of 3D characters is frequently a time-consuming and repetitive process that involves either skeleton-rigging or pose-setting for morph targets. A major issue of concern is the necessity to repeat similar tasks for different models, re-creating the same animation system for several faces. Thus there is a need for reusable methods and tools that allow the introduction of automation into these processes. In this paper we present such a method to assist in the process of facial rigging: the Maskle. Based upon the standard bone-weight linear skinning animation technique, the desired distribution of vertex-movement weights for facial animation is pre-programmed into a low-resolution, generic facial mask. This mask, or ‘Maskle’, is then semi-automatically overlaid onto a newly created face model, before the animation-weight distribution is automatically transferred from the Maskle to the model. The result is a weight-painted model, created semi-automatically, and available for the artist to use for animation. We present results comparing Maskle-weighted faces to those weighted manually by an artist, which were treated as the gold standard. The results show that the Maskle is capable of automatically weight-painting a face to within 1.58% of a manually weighted face, with a maximum error of 3.82%. Comparison with standard professional automatic weighting algorithms shows that the Maskle is over three times more accurate.

Paper Nr: 59
Title:

INTERACTIVE JELLYFISH ANIMATION USING SIMULATION

Authors:

Dave Rudolf and David Mould

Abstract: This paper presents an automatic animation system for jellyfish that accounts for interaction between the organism and its surroundings. We endeavor to model the jellyfish’s morphology, as well as its achieved thrust. We physically simulate the elastic body of the jellyfish and its surrounding sea water. We use a modified immersed boundary method to combine spring-mass systems and a grid-based semi-Lagrangian fluid solver. The resulting simulations are efficient with an acceptable compromise in physical accuracy. We reduce our model for axially symmetric species to 2D, and extrapolate the results to 3D. We add detail to the 3D shape with noise that is inspired by empirical observations of real jellyfish. We also suggest suitable contraction functions so that our virtual jellyfish propells itself within the water in a manner similar to the real organism. The resulting system is capable of animating jellyfish in real-time on modest desktop hardware.

Paper Nr: 71
Title:

NEW CLOSED FORM SOLUTIONS FOR SKELETAL EXTRACTION FROM MOTION CAPTURE

Authors:

Sudhanshhu Semwal and Jonathan Kip Knight

Abstract: We present a fast closed form solution for estimating the exact joint locations inside the human body from motion capture data. The new closed-form solution is more robust and faster. For example, the formulae are as much as about 100 times faster than the traditional non-linear Maximum Likelihood Estimator and about 9 times faster than linear least squares methods. The methods are proven to be statistically efficient when measurement error is smaller than the joint-marker distance. Unbiased Generalized Delogne-Kása (UGDK), multiple radii solution, and incremental GDK are important contributions of our research providing closed form fast solutions for skeleton extraction from motion capture data. Skeletal animation sequences are generated using the CMU and Eric Camper’s motion capture database.

Short Papers
Paper Nr: 19
Title:

SIMPLE FLEXIBLE SKINNING BASED ON MANIFOLD MODELING

Authors:

Franck Hétroy, Cédric Gérot, Lin Lu and Boris Thibert

Abstract: In this paper we propose a simple framework to compute flexible skinning weights, which allows the creation from quasi-rigid to soft deformations. We decompose the input mesh into a set of overlapping regions, in a way similar to the constructive manifold approach. Regions are associated to skeleton bones, and overlaps contain vertices influenced by several bones. A smooth transition function is then defined on overlaps, and is used to compute skinning weights. The size of overlaps can be tuned by the user, enabling an easy control of the desired type of deformations.

Paper Nr: 22
Title:

DATA MINING APPROACH FOR POSITIONING CAMERA IN DISPLAYING MOCAP SEARCH RESULTS

Authors:

Sindharta Tanuwijaya and Yoshio Ohno

Abstract: In recent years, the amount of mocap has accumulated due to its popularity in creating realistic human motions. However, such accumulation is yet to be accompanied by the development of a mocap search engine. In addition to the difficulty in processing mocap search, this phenomenon is also due to the problems in displaying mocap as search results, one of which is determining the camera position, orientation, and distance in displaying mocap. In this paper, we specify camera orientation and distance as constraints to determine camera positions by using available training data which are given as inputs into data mining techniques. In addition, we also discuss a method to select representative frames of mocap, thus allowing for the display of mocap search results as a list of sets of selected mocap frames. Finally, we employ a number of data mining techniques along with a simple method to determine the camera position which yields the widest projection area of a virtual face consisting hands and feet joints into the camera plane, and compare the results to each other.

Paper Nr: 24
Title:

AN EFFICIENT UNDO/REDO-FRAMEWORK FOR THREE-DIMENSIONAL VISUAL SIMULATION OF ALGORITHMS AND DATA STRUCTURES

Authors:

Ashraf Abu Baker

Abstract: In order to be pedagogically effective, an algorithm visualisation is expected to satisfy a large number of requirements. One of the most essential and useful requirements is its ability to provide support for reversing performed user actions. In this work we will introduce a generic concept for an efficient undo/redo framework for three-dimensional visual simulations of algorithms and data structures. The framework uses the memento design pattern to implement a linear multiple-undo/multiple-action model with an unlimited undo of performed actions. It is straightforward to utilise and supports the automated generation of three-dimensional visual simulations of algorithms and data structures.

Paper Nr: 28
Title:

RETARGETING MOTION OF CLOTHING TO NEW CHARACTERS

Authors:

Yu Lee and Moon-Ryul Jung

Abstract: We show how to transfer the motion of cloth from a source to a target body. The obvious method is to add the displacements of the source cloth, calculated from their position in the initial frame, to the target cloth; but this can result in penetration of the target body, because the shape of the target body. To overcome this problem, we compute an approximate source cloth motion, which maintains the initial spatial relationship between the cloth and the source body; then we obtain a detailed set of correction vectors for each frame, which relate the exact cloth to this approximation. We then compute the approximate target cloth motion in the same way as the source cloth motion; and finally we apply the detail vectors that we generated for the source cloth to the approximate target cloth, thus avoiding penetration of the target body. We demonstrate the retargeting of cloth using figures engaged in dance movements.

Paper Nr: 39
Title:

A FRAMEWORK FOR H-ANIM SUPPORT IN NVES

Authors:

Ch. Bouras, K. Chatziprimou, V. Triglianos and Th. Tsiatsos

Abstract: Many applications of Networked Virtual Environment presuppose the users’ representation by humanoid avatars that are able to perform animations such as gestures and mimics. Example applications are computer supported collaborative work or e-learning applications. Furthermore, there is a need for a flexible and easy way to integrate humanoid standardized avatars in many different NVE platforms. Thus, the main aim of this paper is to introduce a procedure of adding animations to an avatar that is complying with H-Anim standard and to present a standardized way to integrate avatars among various NVEs. More specifically this paper presents a framework for adding/loading custom avatars to an NVE and applying to them a set of predefined animations, using H-Anim standard.

Paper Nr: 51
Title:

A METHOD FOR 3D MORPHING USING SLICES

Authors:

Shamima Yasmin and Abdullah Zawawi Talib

Abstract: 3-D morphing, in its simplest definition, is shape transformation between a pair of objects i.e. source and target, by gradual, continuous and simultaneous dissolvement of the shape of source object to its target and vice versa resulting in a number of intermediate shapes. Many algorithms have been developed for this purpose with each one having its own speciality. In this paper, a novel algorithm is presented which is based on slices. The technique originates from the concept of reducing a 3-D object to a number of slices in 2D plane. In the algorithm, all of the 2D slices may not be oriented in either x, y, z or in a particular direction. Orientation and rotation of the slices within a single body can be varied from one slice to another based on the alignment of the object. Oriented Bounding Box (OBB) is used to determine the orientation of the object. The advantages of the proposed method i.e. minimal user input, flexibility, dynamism and ease of implementing over other 3D morphing algorithms are also discussed.

Paper Nr: 72
Title:

SKELETON-BASED RIGID SKINNING FOR CHARACTER ANIMATION

Authors:

Andreas Vasilakis and Ioannis Fudos

Abstract: Skeleton-based skinning is widely used for realistic animation of complex characters defining mesh movement as a function of the underlying skeleton. In this paper, we propose a new robust skeletal animation framework for 3D articulated models. The contribution of this work is twofold. First, we present refinement techniques for improving skeletal representation based on local characteristics which are extracted using centroids and principal axes of the character’s components. Then, we use rigid skinning deformations to achieve realistic motion avoiding vertex weights. A novel method eliminates the artifacts caused by self-intersections, providing sufficiently smooth skin deformation.

Area 4 - Interactive Environments

Full Papers
Paper Nr: 13
Title:

GaDeVi - Game Development Integrating Tracking and Visualization Devices into Virtools

Authors:

Ricardo Aguiar, João Madeiras Pereira and José Braz

Abstract: Computer and console games are increasingly using non-computer conventional input/output devices. This work’s main goal was to create an interactive 3D application with Virtools, a development tool that appeals to the player dexterity and astuteness through the use of several immersive, non-computer conventional devices like magnetic trackers, data gloves and VR glasses. The present paper describes the integration of interaction and visualization devices into Virtools as well as the development of two games using the VR environment. To finalize the assessment of the performance measurements and user tests is given.

Paper Nr: 67
Title:

THE EFFECT OF HAPTIC GUIDES ON HUMAN PERFORMANCE IN VIRTUAL ENVIRONMENTS

Authors:

Sehat Ullah, Samir Otmane, Paul Richard and Malik Mallem

Abstract: In order to make the virtual environments(VE’s) more realistic and to increase human performance, the inclusion of haptic modality becomes more important. In this paper we present two new haptic guides. The haptic guides are fundamentally aimed to assist users for object selection in VE’s. We divide the virtual environment into three zones. In the first zone the user can freely move and don’t use any sort of guides. In the 2nd zone, user is given visual guidance and the 3rd zone contains haptic guides along with visual guides. As the paper presents two different models of the haptic guides, one for free and multidirectional selection and the second for precise and single direction selection. We not only study the effect of these guides on human task performance in the VE but also investigate a comparison of the two haptic models.

Paper Nr: 82
Title:

EVALUATION OF VISUALIZATION FEATURES IN THREE-DIMENSIONAL LOCATION-BASED MOBILE SERVICES

Authors:

Mário Freitas, António Augusto de Sousa and António Coelho

Abstract: Nowadays, there is a wide range of commercial LBMS (Location-Based Mobile Services) available in the market, mainly in the form of GPS-based navigation solutions, and a trend towards the display of 3D maps can be clearly observed. Given the complete disparity of ideas and a visible commercial orientation in the industry, the study of the visualisation aspects that influence user performance and experience in the exploration of urban environments using 3D maps becomes an important issue. In this work, a generic conceptual framework is proposed whose main purpose is to objectively evaluate the impact and contribution of the major visualisation elements involved (henceforth mentioned as feature vectors). With this framework in mind, an online questionnaire was developed and administered to 149 test subjects in order to measure the real impact of feature vectors. The results clearly demonstrated that certain features have clear impact on user performance, and should be taken in account in LBMS development. As an example, just by displaying buildings with a 3D appearance, subjects were able to match more accurately the real environment with the one presented on a mobile device. In general, users were able to perform the tasks entrusted to them faster, if they were provided more realistic imagery.

Paper Nr: 83
Title:

iiBOARD - Development of a Low-Cost Interactive Whiteboard using the Wiimote Controller

Authors:

Marco Silva, Luís Paulo Reis, Armando Sousa, Brígida Mónica Faria and A. Pedro Costa

Abstract: Interactive whiteboards are gaining importance in our society, both at a business level and, especially, at an educational level. However, the products offered by the major manufacturers have a major barrier to their acquisition: very high prices. There is an urgent need to use new technologies in order to provide solutions that present the same performance levels than typical interactive whiteboards, but with a significantly reduced cost. Throughout this paper the steps taken for the development of an innovative low-cost interactive whiteboard are described. The proposed system is based on the Wii Remote command of the Nintendo Wii video-game console. This command, although very inexpensive has an infrared camera, and supports Bluetooth communication. The system control is based on a wireless device, based on infrared emitters, which supports most of the mouse events. A complete whiteboard application was also developed using Borland Delphi for Windows. This application may be used with either one or two Wiimotes and has a very simple and efficient calibration method. The application also includes viewing capabilities of some of the Wiimote characteristics, as well as a flexible Notebook to increase its range of possible uses. The results obtained through a survey conducted to a small set of whiteboard users were very positive indicators about the acceptance of the inexpensive solution proposed.

Paper Nr: 85
Title:

AUGMENTED REALITY INTERACTION TECHNIQUES - Design and Evaluation of the Flip-Flop Menu

Authors:

Mickael Naud, Paul Richard and Jean-Louis Ferrier

Abstract: We present the evaluation of a bimanual augmented reality (AR) interaction technique, and focus on the effect on viewpoint and image reversal on human performance The interaction technique (called flip-flop) allows the user to interact with a 3D object model by using a V-shaped AR menu placed on a desk in front of her/him. The menu is made of two complementary submenus. Both submenus (master and slave) are made of four Artag fiducial markers. The functionalities of the slave submenu are the following : (1) increase/decrease the size or rotate/stop the 3D object, (2) apply a color (one over four) or (3) a 2D texture (one over four) on the 3D object and (4) apply predefined material parameters. Each event is triggered by a masking of a Artag marker by the the user’s right or left hand. 40 participants were instructed to perform actions such as rotate the object, apply a texture or a color on it, etc. The results revealed some difficulties due to the inversion of the image on the screen. Finally, although the proposed interaction technique is currently used for product design, it may also be applied to other fields such as edutainment, cognitive/motor rehabilitation, etc. Moreover, other tasks than the ones tested in the experiment may be archived using the menu.

Short Papers
Paper Nr: 34
Title:

EFSAT - An Exact and Efficient Triangle Intersection Test Hardware

Authors:

Andreas Raabe, Jan Tietjen and Joachim K. Anlauf

Abstract: Software implementations that test two triangles for intersection often favour speed over exact calculation. They leave it to the user to choose an exact or a fast test depending on the domain of application. Hardware implementations can not opt to make this distinction since users will always expect an accelerator hardware to be applicable in all possible settings. This paper introduces a novel approach towards exact intersection testing of triangles. It is based on the separating axes test and lends itself well to hardware implementation. To be integrable into a hierarchical collision detection design this test needs to be extremely resource efficient. Thus, it does not iterate until an exact solution is found, but instead categorises results as correct and possibly incorrect. It is implemented using 18-bit fixed-point numbers, while still maintaining resolutions that can keep up with double-precision floating-point implementations. The proposed test is integrated into a hierarchical collision detection FPGA-design accelerating collision queries by an order of magnitude. In a realistic benchmark less than 0:9% of possibly incorrect results are reported without impairing system performance.

Paper Nr: 60
Title:

ENHANCING VIRTUAL ENVIRONMENT-BASED SURGICAL TEAMWORK TRAINING WITH NON-VERBAL COMMUNICATION

Authors:

Stefan Marks, Burkhard Wünsche and John Windsor

Abstract: Virtual reality simulations for training surgical skills are increasingly used in medical education and have been shown to improve patient outcome. While advances in hardware and simulation techniques have resulted in many commercial applications for training technical skills, most of these simulators are extremely expensive and do not consider non-technical skills like teamwork and communication. This is a major drawback since recent research suggests that a large percentage of mistakes in clinical settings are due to communication problems. In addition, training teamwork can also improve the efficiency of a surgical team and as such reduce costs and workload. We present an inexpensive camera-based system for capturing aspects of non-verbal communication of users participating in virtual environment-based teamwork simulations. This data can be used for the enhancement of virtual-environment-based simulations to increase the realism and effectiveness of team communication.

Paper Nr: 61
Title:

iTILE FRAMEWORK FOR CONSTRUCTING INTERACTIVE TILED DISPLAY APPLICATIONS

Authors:

Seokhwan Kim, Minyoung Kim, Yonjoo Cho and Kyoung Shin Park

Abstract: We describe a new scalable display framework, called iTILE, designed to help ease the development of interactive graphics applications that run on a large tiled display. The framework supports the execution of multiple interactive scene-graph applications, synchronized rendering, distributed data sharing, and unified user interface mechanism on a cluster-driven tiled display. It enables the application window launching, moving and resizing on a tiled display that requires a dynamic reconfiguration of rendering nodes. It also provides the standardized method to support various input devices for the interactive contents. This paper presents the design and the implementation of iTILE architecture and a few applications built using this framework.

Paper Nr: 77
Title:

OPTIMIZING THE MANAGEMENT AND RENDERING OF RAIN

Authors:

Anna Puig-Centelles, Oscar Ripollesa and Miguel Chover

Abstract: Current rain solutions are capable of offering very realistic images. Nevertheless, this realism often involves extremely high rendering costs. Our proposal is aimed at facilitating the creation and management of rain scenes. On the one hand, we define the areas in which it is raining and, on the other hand, we perform a suitable management of the particle systems inside them. The latter step is reached by means of level-of-detail techniques which are applied directly in the Geometry Shader by modifying the size and the number of rendered particles. Our results prove that fully-integrating the level-of-detail management in the GPU considerably increases the final performance.

Paper Nr: 78
Title:

OBJECTS VISUALIZATION IN DIGITAL TERRAINS USING ADAPTIVE VIEW-DEPENDENT TECHNIQUES

Authors:

Rafael Moreira Savelli, Roberto de Beauclair Seixas, Anselmo Antunes Montenegro and Esteban Walter Gonzalez Clua

Abstract: There are many applications involving featured terrains visualization. One of them is for gaming purposes. However, when dealing with real data, many of this applications fail to cope with such information. So, this work presents an efficient way to minimize or even remove this kind of problem. We propose a method based on image-based rendering and view-dependent visualization techniques. These methods were applied in terrain visualization with real vegetation data where distribution and type is determined from digital satellite images.

Paper Nr: 86
Title:

KNOWLEDGE AT YOUR FINGERTIPS - Multi-touch Interaction for GIS and Architectural Design Review Applications

Authors:

Yvonne Jung, Jens Keil, Harald Wuest, Timo Engelke, Patrick Riess and Johannes Behr

Abstract: This paper introduces novel techniques of interacting and controlling 3D content using multi-touch interaction principles for navigation and virtual camera control. Based on applications from GIS and for the architectural design review process, implementation and usage of these interaction techniques are illustrated. A comprehensive hardware and software setup is used, which not only includes tracking, but also an X3D based layer to simplify application development. Therefore it allows designers and other non-programmers to develop multi-touch applications very efficiently, while allowing to focus on user interaction and content.

Paper Nr: 88
Title:

ARE HAPTICS-ENABLED INTERACTIVE AND TANGIBLE CINEMA, DOCUMENTARIES, 3D GAMES, AND SPECIALIST TRAINING APPLICATIONS OUR FUTURE?

Authors:

Miao Song and Peter Grogono

Abstract: Interactive augmented reality via tangible media and cinema enabled with responsive environments through haptic devices providing the physical feedback from a virtual space to the real space to the interacting audience is becoming more common especially now that computer graphics and other visual stimuli are becoming so photorealistic and where they fail, the brain makes up the missing details. This covers games, cinema, virtual reality applications and education applications. It seems that so common that we will all live in a couple of decades in an interactive virtually-enhanced world where we won’t be able some times to tell apart the virtual and the real. How will this affect the upcoming generations and child education? Will we be out of touch with the reality like in the Matrix (Wachowski and Wachowski, 1999)? While possibly accepting the upcoming inevitable change, can we improve on it early on and turn it to our advantage? If so, how? We present the initial research steps as a part of this work to start answering these questions.

Posters
Paper Nr: 32
Title:

SYNCHRONIZING USER INTERACTIONS WITH MULTIPLE PARAMETRIZED THREE-DIMENSIONAL WEB GRAPHICS

Authors:

Martin Kraus

Abstract: The synchronization of a single user’s interactions with multiple parametrized graphics in a single web page is an important and powerful feature of interactive illustrations. In this work we present an interface to specify this kind of synchronization and its implementation in a Java applet for rendering and interacting with threedimensional web graphics. Our design allows authors of web pages to synchronize the parameters of groups of interactive graphics within a web page by specifying identical text labels for all applets of the same group. Further labels may be specified to synchronize changes of the viewpoints and/or of the magnification. This design allows for multiple, independently synchronized groups of graphics on the same web page as well as any combination of synchronized parameters, viewpoints and magnification factors. Only three additional applet parameters are necessary, which are not restricted by any syntax.

Paper Nr: 64
Title:

EVALUATING VISUALISATION AND NAVIGATION TECHNIQUES FOR INTERPRETATION OF MRA DATA

Authors:

B. W. van Schooten, E. M. A. G. van Dijk, E. V. Zudilova-Seinstra, P. J. H. de Koning and J. H. C. Reiber

Abstract: We argue that a more systematic treatment of the many existing options for medical volume visualisation is desirable. We show that combining the most common medical visualisation and navigation techniques in a systematic way leads to a meaningful set of interesting and sometimes novel UI techniques. We also propose a technique for using generated data and tasks suited to non-medical users for conducting user experiments. We evaluate the UI techniques qualitatively to arrive at a set of promising techniques for future research.

Paper Nr: 87
Title:

OPENGL PROJECT PRESENTATION SLIDES INTERFACE AND A CASE STUDY

Authors:

Serguei A. Mokhov and Miao Song

Abstract: We present a concept of a 3D interface to power-point-like presentations using OpenGL. We argue the presentations of such kind are a lot more useful to demonstrate projects, conference talks, or computer graphics education tutorials and lectures with the results of 3D animation, effects, and others alongside with the presentation in place instead of switching between a regular presentation software to the demonstration and back – the demo and the presentation are combined together in one unit and can serve as an educational piece on its own.