GRAPP 2011 Abstracts


Area 1 - Geometry and Modeling

Full Papers
Paper Nr: 1
Title:

TOOL PATH PLANNING IN FLANK MILLING BASED ON DUAL SPHERICAL SPLINE

Authors:

Yayun Zhou

Abstract: The flank milling (side milling) method, which uses the manufacturing tool side to remove material, is widely used in industry to manufacture ruled surfaces. Ruled surfaces are often used in blade design considering the aerodynamics requirements and the manufacture cost. A common way to derive a flank millable blade surface is to adopt a certain ruled surface approximation algorithm before the surface is delivered to the manufacturer. In this paper, a new tool path planning approach is proposed based on the offset theory and the kinematic ruled surface approximation. The novelty of this approach is to denote the drive surface as a dual spherical spline, which is a new ruled surface representation. This drive surface is derived by kinematically approximating the offset surface of the original design as a ruled surface. Therefore, the designed blade surface is represented as a flank milling tool path with a cylindrical cutter in CNC machining. This approach delivers more accuracy compared with convectional tool position optimization methods. By integrating the manufacture requirements into the design phase, this approach also reduces the developing cycle time and the manufacturing cost.

Paper Nr: 7
Title:

NOSE TIP DETECTION AND TRACKING IN 3D VIDEO SEQUENCES

Authors:

Xiaoming Peng and Mohammed Bennamoun

Abstract: Point cloud data processing is an important topic in geometric computing. One promising application of point cloud data processing is 3D face recognition. With the recent developments of 3D scanning technology, the emergence in the near future of 3D face recognition from 3D video sequences is eminent. Face tracking is a necessary step before the recognition of a face. In this paper, we propose the integration of a nose tip detection method into the process of tracking the face in a 3D video sequence. The nose tip detection method which does not require training nor does it rely on any particular model, can deal with both frontal and non-frontal poses, and is quite fast. Combined with the Iterative Closest Point (ICP) algorithm and a Kalman filter, the nose-tip-detection-based method achieved robust tracking results on real 3D video sequences. We have also shown that it can be used to coarsely estimate the roll, yaw and pitch angles of the face poses.

Paper Nr: 11
Title:

A UNIFIED APPROACH TO GEOMETRIC MODELING OF CURVES AND SURFACES

Authors:

L. H. You and Jian J. Zhang

Abstract: A unified approach to geometric modeling of curves and surfaces is given. Both a vector-valued fourth and sixth order partial differential equations (PDEs) of motion are proposed. The fourth order PDE covers all existing PDEs used for surface modeling, and the sixth order PDE considers the curvature effect on curves and surfaces. In order to apply these PDEs to create curves and surfaces in real time, we have presented a composite power series method which guarantees the exact satisfaction of boundary conditions, and represents curves and surfaces with analytical mathematical formulae. We have examined the accuracy and efficiency of the proposed method, and employed it to a number of applications of static and dynamic modeling of curves and surfaces, including free-form surface generation and surface blending. It is found that this method has similar computational accuracy and efficiency to the corresponding closed form solution method, and creates curves and surfaces far more efficiently and accurately than numerical methods. In addition, it can deal with complicated shape modeling problems..

Paper Nr: 12
Title:

TRIGONOMETRIC CURVE-BASED HUMAN MODELING

Authors:

L. H. You and X. S. Yang

Abstract: In this paper, we present a modeling method to build human models. A human model is divided into different parts. For each part, cross-section curves are created and approximated with trigonometric series. All parts are constructed from these trigonometric curves and assembled together to create the whole human model. Since surface creation of human models is transformed into generation of cross-sectional curves and few design parameters are required to describe these cross-sectional curves, our approach can decrease the data size of geometric modeling greatly and is especially suitable for reconstruction of human models from scanned point clouds.

Paper Nr: 18
Title:

A RAY TRACING BASED MODEL FOR 3D LADAR SYSTEMS

Authors:

Tomas Chevalier

Abstract: This paper describes an approach to simulate long range laser based 3D imaging sensor systems. The model is based on a ray tracing principle where a large amount of rays are sent from a sensor towards the scene. The scene, the target surface, and the atmosphere affect the rays and the final light energy distribution is acquired by a receiver, where sensor data is generated. The approach includes advanced descriptions of the materials in the scene, and modeling of several effects in the atmosphere and the receiver electronics. A turbulence model is included to achieve realistic long range simulations. Examples of simulations and corresponding real world data collection are shown. Model validations are presented.

Paper Nr: 24
Title:

USER-GUIDED FEATURE SENSITIVE HOLE FILLING FOR 3D MESHES

Authors:

Hanh T.-M. Ngo and Won-Sook Lee

Abstract: Most hole filling approaches use techniques to fill up a hole first and then to smooth it. Very few tries rebuild features on the filled surface of the original 3D model. We propose an efficient hole-filling methodology which preserves sharp features of the geometry of the original model. The main idea is that we reconstruct feature curves in the missing parts of the given mesh before filling the hole with smoothing surface. The feature curves in the missing part are reconstructed by extending salient features of the existing parts. The hole is partitioned into several smaller and more planar sub-holes divided by the feature curves and then the hole-filling step follows. User intervention is available to design the features to be desired shape to guide feature curve reconstruction wherever ambiguity exists or results are unsatisfactory. Our hole filling techniques is different from other existing techniques as features are taken as the first subject to reconstruct, which eventually drive the feature-definite surface filling process. It is also very efficient as a user is interfering only with features and the actual hole-filling step is dealing with only planar holes.

Paper Nr: 57
Title:

INHOMOGENEOUS AXIAL DEFORMATION FOR ORTHOPEDIC SURGERY PLANNING

Authors:

Sergei Azernikov

Abstract: Intuitive global deformation of complex geometries is very important for many applications. In particular, in the biomedical domain, where interactive manipulation of 3D organic shapes is becoming an increasingly common task. Axial deformation is natural and powerful approach for modeling of tubular structures, like bones. With this approach, the embedding space is associated with deformable curve, the handle axis, which guides deformation of the embedded model. As a result, the produced deformation is homogeneous and independent of the model representation and shape. However, in many situations it is beneficial to incorporate geometric and physical properties of the model into the deformation formulation. This leads to inhomogeneous axial deformation which allows to achieve more intuitive results with less user interaction. In this work, the inhomogeneous axial deformation is achieved through deformation distribution function (DDF) induced on the guiding axis by the embedded model. Since with the proposed formulation the DDF can be pre-computed, run-time computational complexity of the method is similar to the original axial deformation approach.

Paper Nr: 63
Title:

REALISTIC 3D SCENE RECONSTRUCTION FROM UNSCONSTRAINED AND UNCALIBRATED IMAGES TAKEN WITH A HANDHELD CAMERA

Authors:

Minh Hoang Nguyen and Burkhard Wünsche

Abstract: We address the problem of reconstructing 3D scenes from a set of unconstrained images. These image sequences can be acquired by a video camera or handheld digital camera without requiring calibration. Our approach does not require any a priori information about the cameras being used. The camera's motion and intrinsic parameters are all unknown. We use a novel combination of advanced computer vision algorithms for feature detection, feature matching, and projection matrix estimation in order to reconstruct a 3D point cloud representing the location of geometric features estimated from input images. In a second step a full 3D model is reconstructed using the projection matrix and a triangulation process. We demonstrate with data sets of different structures obtained under different weather conditions that our algorithm is stable and enables inexperienced users to easily create complex 3D content using a simple consumer level camera.

Short Papers
Paper Nr: 21
Title:

EFFICIENT UNIFORM GRIDS FOR COLLISION HANDLING IN MEDICAL SIMULATORS

Authors:

Marc Gissler

Abstract: We investigate spatial acceleration structures within collision handling in scenarios with ”worst-case” spatial layout. These are scenarios where lots of collisions and interactions persist over large time intervals. We focus on acceleration structures based on uniform grids and assess their efficiency in construction, update and query. Z-curves as a technique for the mapping of spatial locality to uniform grids are analyzed to improve the cache-hit rate. The findings are applied to a deformable collision framework. Experiments are performed on scenarios that are typical for medical simulators. They often exhibit the ”worst case” spatial layout mentioned above.

Paper Nr: 25
Title:

EFFICIENT DYNAMICAL COMPUTATION OF PRINCIPAL COMPONENTS

Authors:

Darko Dimitrov and Mathias Holst

Abstract: In this paper we consider the problem of updating principal components of a point set in $\mathbb{R}^d$ when points are added or deleted from the point set. A recent result of \cite{Pebay-08} implies an efficient solution for that problem when points are added to a discrete point set. Here, we extend that result for deletions in the discrete case, and for both additions and deletions for continuous point sets in $\mathbb{R}^2$ and $\mathbb{R}^3$. In both cases, discrete and continuous, no additional data structures or storage are needed for computing the new principal components. An important application of the above results is the dynamical computation of bounding boxes based on principal component analysis. PCA bounding boxes are very often used in many fields, among others in computer graphics, for example, for ray tracing, fast rendering, collision detection, or video compression algorithms. Since some version of PCA bounding boxes have guaranties on their size (volume), they are also of interest in applications where the guaranty of the approximation quality is required. We have designed and implemented algorithms for computing dynamically PCA bounding boxes in $\mathbb{R}^3$.

Paper Nr: 26
Title:

PARAMETRIC MODELING OF TRUNK-ROOT JUNCTIONS USING ASTROIDAL EXPANSION GEOMETRY

Authors:

Karthik Mahesh Varadarajan

Abstract: In the field of foliage or vegetation modeling for computer graphics, algorithms for parametric modeling of trees have largely focused on branching mechanisms with little emphasis on modeling the base of the trunk, especially the trunk-root junctions. Roots and trunk-root junctions that appear prominently above the ground in the case of many species of trees such as the Ficus macrophylla and the Picea sitchensis as a result of age and soil erosion are usually completely neglected by traditional trunk modeling methods. In this paper, we introduce a novel parametric modeling scheme to build such trunk-root junctions, while providing for an elegant framework to construct the bases of trunks and branches in order to provide better characterization for a variety of flora species. The paper also describes novel schemes for generating branch junctions and for rendering tree barks.

Paper Nr: 40
Title:

DYNAMIC AND ADAPTIVE TESSELLATION OF BÉZIER SURFACES

Authors:

R. Concheiro and M. Amor

Abstract: Bézier surfaces offer powerful mechanisms to describe high quality models in computer graphics. In this paper we present a methodology for the implementation of the adaptive tessellation of Bézier models on the GPU. Tessellation is performed with variable resolution inside the patch to permit the use of meshes with a lower number of triangles but preserving a high visualization quality. Primitives are dynamically generated according to the results of local subdivision tests. The locality of the decisions assures that contiguous triangles are coherently subdivided.The resulting procedure is efficient, simple and generates the tessellation pattern of each Bézier surface dynamically. This enables tessellation of complex models to be performed in real time.

Paper Nr: 42
Title:

ROBUST FEATURE LINE EXTRACTION ON CAD TRIANGULAR MESHES

Authors:

Vincent Vidal

Abstract: Feature lines are perceptually salient features on 3D meshes. They are of interest for 3D shape description, analysis and recognition. Their detection is a necessary step in several feature sensitive mesh processing applications such as mesh simplification, remeshing or non-photorealistic rendering. In this paper, an estimator for the angle between tangent plane normals is introduced and a new automatic method is proposed for robust detection of crest lines on 2-manifold triangular meshes, in particular Computer-Aided Design models. The method integrates learning into a global minimization framework favoring geometrically coherent solutions. We study our method in detail and compare it with other methods for the detection of feature edges on 3D meshes. Our comparative results indicate that our method outperforms classical techniques especially in the presence of noise.

Paper Nr: 60
Title:

ILLUMINATING AND RENDERING HETEROGENEOUS PARTICIPATING MEDIA IN REAL TIME USING OPACITY PROPAGATION

Authors:

Anthony Giroud and Venceslas Biri

Abstract: We present a new approach to illuminate and render single scattering effects in heterogeneous participating media in real time. The medium’s density is modeled as a sum of radial basis functions, and is then sampled into a first volumetric grid. We then integrate the extinction function from each light source to each cell in the volume by a fast cell-to-cell propagation process on the GPU, and store the result in a second volume. We finally render both scattering medium and surfaces using a regular step ray-marching from the observer to the nearest surface. As we traverse the medium, we fetch data from both volumes and approximate a solution to the scattering equation. Our method is real-time, easy to implement and to integrate in a larger pipeline.

Paper Nr: 66
Title:

SKETCH-BASED BUILDING MODELLING

Authors:

David J. Olsen and Nathan D. Pitman

Abstract: Computer generated 3D models of buildings are an important component of many computer graphics applications. Rapid and easy-to-use modelling techniques are often more important than the ability to create precise and detailed geometry. We present a sketch-based modelling tool for the rapid creation of rough 3D building models. The algorithm analyses the sketch input, extracts shape and detail information, predicts the building type, creates 3D models using three different reconstruction techniques, and adds building details using a displacement texture. A user study confirms that the algorithm is easy to use, intuitive, efficient and fun.

Area 2 - Rendering

Full Papers
Paper Nr: 17
Title:

OUTDOOR ILLUMINATION ESTIMATION IN IMAGE SEQUENCES FOR AUGMENTED REALITY

Authors:

Claus B. Madsen and Brajesh B. Lal

Abstract: The paper presents a technique for estimating the radiance of the sky and sun for outdoor, daylight illumination conditions. Shadows cast by dynamic objects are detected using color imagery, combined with depth information from a commercial stereo camera setup. Color information extracted from the detected shadows is used to estimate the radiance of the sun. The technique does not require special purpose objects in the scene, nor does it require High Dynamic Range imagery. Results are demonstrated by rendering augmented objects into real images with shading and shadows which are consistent with the real scene.

Paper Nr: 44
Title:

TRAVERSING A BVH CUT TO EXPLOIT RAY COHERENCE

Authors:

R. Torres

Abstract: In this paper we study how to deal with the ray incoherence that naturally arises in path tracing-based systems. We introduce the notion of BVH Cut to split the tree into a forest of disjoint subtrees. We will use it to filter the rays that are successively generated by the path tracing algorithm. Each subtree is then traversed by its corresponding group of rays. Despite the overload of filtering all the rays each time, a significant profit is achieved. Nevertheless, constructing a BVH cut is a challenging task, because it can lead to a huge amount of work if the same rays belongs to many groups. Thus, we present two kind of building heuristics: structural heuristics that characterizes the root of a subtree by a property (the node’s depth or the surface area of its bounding volume in this paper), and optimization heuristics that are based on the Simulated Annealing method. The performance of traversing the cuts so built has been experimentally analyzed over four usual scenes, using two popular implementations of the subtree traversal (persistent while-while / persistent packet). The results show a relevant saving time w.r.t. the classic BVH traversal, that grows as the ray incoherence increases. The best saving ranges from 32.0% / 40.9% for structural heuristics, to 32.0% / 51.7% for cuts built with Simulated Annealing.

Short Papers
Paper Nr: 4
Title:

USING OPAQUE IMAGE BLUR FOR REAL-TIME DEPTH-OF-FIELD RENDERING

Authors:

Martin Kraus

Abstract: While depth of field is an important cinematographic means, its use in real-time computer graphics is still limited by the computational costs that are necessary to achieve a sufficient image quality. Specifically, color bleeding artifacts between objects at different depths are most effectively avoided by a decomposition into subimages and the independent blurring of each sub-image. This decomposition, however, can result in rendering artifacts at silhouettes of objects. While various algorithms have been suggested to eliminate these artifacts, we propose a new blur filter that increases the opacity of all pixels to avoid artifacts at the cost of physically less accurate but still plausible rendering results. The proposed filter is named “opaque image blur” and is based on a glow filter that is applied to the alpha channel. We present a highly efficient GPU-based pyramid algorithm that implements this filter for depth-of-field rendering.

Paper Nr: 15
Title:

GLOBAL ILLUMINATION USING IMPERFECT VOLUMES

Authors:

Pavlos Mavridis and Georgios Papaioannou

Abstract: This paper introduces the concept of imperfect volumes, a fast one-pass point-based voxelization algorithm, and presents its applications to the global illumination problem. As often noted, diffuse indirect illumination has the characteristics of a low frequency function, consisting of smooth gradations. We exploit this by performing the indirect lighting computations on a rough approximation of the scene, the imperfect volume. The scene is converted on the fly to a dense point cloud, and each point is directly rendered to a volume texture, marking the corresponding voxel as occupied. A framebuffer reprojection scheme ensures that voxels visible to the main camera will get more points. Ray-marching is then used to compute the ambient occlusion or the indirect illumination of each voxel, and the results are stored using spherical harmonics. We demonstrate that the errors introduced by the imperfections in the volume are small and that our method maintains a high frame rate on scenes with high geometric complexity.

Paper Nr: 35
Title:

CONTENT-SENSITIVE SCREENING IN BLACK AND WHITE

Authors:

Hua Li and David Mould

Abstract: Traditional methods produced unsatisfactory uniform screening. Often additional tones are added to improve the quality of tone and structure. In this paper, we try to produce screening with diverse patterns and with natural structure preservation while still using only one color of ink. We propose several extensions to contrast-aware halftoning including new weight distributions and variations on the priority-based scheme. Patterns can be generated by excluding pixels in a purposeful way and by organizing different groups of input edges based on user interest. Segmented regions are assigned different patterns, based on statistical measurements of the content of each region. Our method can automatically and efficiently produce effective screening with a lot of flexibility and without artifacts from segmentation or false edges.

Paper Nr: 45
Title:

FLEXIBLE CLIPMAPS FOR MANAGING GROWING TEXTURES

Authors:

Dirk Feldmann

Abstract: Previous work on large image data sets has evolved techniques for handling representations of these data that cache textures of arbitrary, but fixed, size in a limited amount of physical memory for rendering in realtime. In these approaches the texture data is usually pre-processed and arranged, for instance in a geometry-independent texture clipmap. New technologies in the area of remote sensing generate aerial images in realtime at a high rate in a patchwork-like pattern, and new images may replace previously captured image data. These patchwork-like image data can be used to create a growing texture which is dynamic in the sense that it may be updated in parts and grow in extension in the course of time. For such growing textures, current clipmap techniques are not appropriate. In this paper we introduce the Flexible Clipmap, a technique for incrementally generating a clipmap from a large virtual texture of dynamically changing content and extent. Our technique makes use of a tile-based clipmap approach and a common spatial indexing data structure to provide access to very large growing textures. We present an evaluation of our technique in the context of a remote sensing application which demands real-time rendering of growing texture data.

Paper Nr: 52
Title:

REAL-TIME TERRAIN RENDERING WITH INCREMENTAL LOADING FOR INTERACTIVE TERRAIN MODELLING

Authors:

Simon van den Hurk

Abstract: Real-time terrain rendering techniques usually employ static data structures and do not allow interactive modification of the terrain. In this paper we describe a real-time geometric clipmapping terrain rendering technique for large terrains which allows incremental updates of the underlying data structure. We have combined the method with an interactive sketch-based terrain modelling technique. The clipmap data structure is updated during runtime to synchronise the terrain visualization with changes to the underlying digital elevation map. Tests and examples demonstrate the advantages of our method over traditional approaches. Disadvantages and limitations are discussed and suggestions for future work are presented.

Paper Nr: 58
Title:

MORPHOLOGICAL ANTIALIASING AND TOPOLOGICAL RECONSTRUCTION

Authors:

Adrien Herubel

Abstract: Morphological antialiasing is a post-processing approach which does note require additional samples computation. This algorithm acts as a non-linear filter, ill-suited to massively parallel hardware architectures. We redesigned the initial method using multiple passes with, in particular, a new approach to line length computation. We also introduce in the method the notion of topological reconstruction to correct the weaknesses of postprocessing antialiasing techniques. Our method runs as a pure post-process filter providing full-image antialiasing at high framerates, competing with traditional MSAA.

Paper Nr: 59
Title:

EFFICIENT ANALYTICAL INTEGRATION OF SINGLE SCATTERING FUNCTION

Authors:

Umashankar Pradhan and Subodh Kumar

Abstract: Light scattering through a participative medium has a significant impact on display. However, accurate and efficient simulation of scattering remains challenging. Monte Carlo or numerical integration techniques are commonly employed to solve the scattering equation. Single scattering is a common approximation that provides satisfactory results in many cases. Analytical integration of scattering under certain assumptions have been achieved by pre-computing a table of values. We present a new approximation to the single scattering equation that is easily integrable in real time. We analyze the error of this approximation and show that the numerical error is insignificant. The images are virtually indistinguishable from those obtained by the more accurate integration.

Posters
Paper Nr: 16
Title:

A COMPARATIVE STUDY OF THE MARCHING CUBES TECHNIQUES FOR 3D REAL-TIME RENDERING OF SCENES IN VIDEOCONFERENCING SYSTEMS

Authors:

Maria Ángeles Calabuig and Moisés Ferrer

Abstract: This paper presents a comparative study of the Marching Cubes techniques and describes their optimised implementations for a 3D videoconferencing system with the aim of obtaining maximum efficiency and flexibility. Different approaches in the CPU and in the GPU are compared in order to analyze the influence of the rendering process in the reconstruction algorithm. To do this, several 3D scenes were captured, codified and sent to a real-time rendering system that reconstructs 3D models at high speed.

Paper Nr: 43
Title:

SCENE DATA SYNCHRONIZATION IN SORT-FIRST RENDERING SYSTEM FOR LARGE DYNAMIC SCENES

Authors:

He Bing and Wang Yangzihao

Abstract: In this paper we built a cluster-based sort-first rendering system. Unlike previous sort-first rendering systems for static scenes, ours can cope with large dynamic scenes with massive data. A set of strategies are designed and implemented to give solutions for scene data synchronization in our system. The experimental results show that our system maintains favorable data consistency for dynamic scenes and is highly scalable with solid improvement of rendering performance. Using 16 computing nodes, our system can achieve interactive visualization result in the test physical simulation scene which contains 10,000 moving rigid-body models and building models with massive geometric and texture data.

Paper Nr: 53
Title:

IMPORTANCE-DRIVEN VOLUME RENDERING AND GRADIENT PEELING

Authors:

Xiao Li and Shengzhou Luo

Abstract: Volume rendering is widely used in visualizing and exploring volume datasets. In volume visualization, it is challenging to obtain desired results, because different tissue types are represented in overlapping ranges of scalar values and interesting structures will be partly or completely occluded by surrounding tissue of less importance. This paper introduces importance-driven volume rendering and gradient peeling techniques to reveal inner structures of interest. The importance of clusters is specified interactively and composited into the opacity of voxels. Then gradient peeling is performed on the clusters whose importance is greater than the user-defined threshold. This semi-automatic approach provides users with the freedom to visualize clusters of interest and the ability to peel off surface layers of the material. Experiment results show that our approach has superior capability in revealing inner structures and removing surrounding tissue which occludes the tissue of interest.

Paper Nr: 55
Title:

ADABOOST GPU-BASED CLASSIFIER FOR DIRECT VOLUME RENDERING

Authors:

Oscar Amoros

Abstract: In volume visualization, the voxel visibility and materials are carried out through an interactive editing of Transfer Function. In this paper, we present a two-level GPU-based labeling method that computes in times of rendering a set of labeled structures using the Adaboost machine learning classifier. In a pre-processing step, Adaboost trains a binary classifier from a pre-labeled dataset and, in each sample, takes into account a set of features. This binary classifier is a weighted combination of weak classifiers, which can be expressed as simple decision functions estimated on a single feature values. Then, at the testing stage, each weak classifier is independently applied on the features of a set of unlabeled samples. We propose an alternative representation of these classifiers that allow a GPU-based parallelizated testing stage embedded into the visualization pipeline. The empirical results confirm the OpenCL-based classification of biomedical datasets as a tough problem where an opportunity for further research emerges.

Area 3 - Animation and Simulation

Full Papers
Paper Nr: 19
Title:

ANIMATION OF AIR BUBBLES WITH SPH

Authors:

Markus Ihmsen and Julian Bader

Abstract: We present a physically-based multiphase model for simulating water and air bubbles with Smoothed Particle Hydrodynamics (SPH). Since the high density ratio of air and water is problematic for existing SPH solvers, we compute the density and pressure forces of both phases separately. The two-way coupling is computed according to the velocity field. The proposed model is capable of simulating the complex bubble flow, e. g. path instability, deformation and merging of bubbles and volume-dependent buoyancy. Furthermore, we present a velocity-based heuristic for generating bubbles in regions where air is likely trapped. Thereby, bubbles are generated on the fly, without explicitly simulating the air phase surrounding the liquid. Instead of deleting the bubbles when they reach the surface, we employ a simple foam model. By incorporating our model into the predictive-corrective SPH method, large time steps can be used. Thus, we can simulate scenarios of high resolution where the size of the bubbles is small in comparison to the liquid volume.

Paper Nr: 23
Title:

INTERACTIVE SIMULATION OF SHIP MOTIONS IN RANDOM SEAS BASED ON REAL WAVE SPECTRA

Authors:

José Miguel Varela and Carlos Guedes Soares

Abstract: The current paper presents a methodology to compute and represent the ship motions at interactive frame rates, when navigating on a virtual sea defined by a real wave spectrum. The Inverse Discrete Fast Fourier Transform algorithm is used to compute the sum of all ship motions components induced by the waves and get the final irregular ship motion. Currently, this is the most efficient method to simulate the ship motions in interactive ocean simulations using wave spectra to describe the sea states. The visual realism and physical accuracy of the simulations turns this method into a powerful tool for developing interactive ship simulators.

Short Papers
Paper Nr: 62
Title:

SKETCHED INTERACTION METAPHORS FOR CHARACTER ANIMATION

Authors:

Konstantin Schauwecker and Simon van den Hurk

Abstract: The use of 3D virtual worlds is increasing rapidly and new tools are necessary to enable untrained users to create 3D content and interact with it. In this paper we present and evaluate sketch-based interaction metaphors for specifying complex animations of 3D skeletally animated models. Sketched interactions include bone rotation, motion path translation, sequencing and synchronisation of animations, and an undo-functionality. The sketches are drawn directly onto a model in a 3D view and are translated into time-dependent joint transformations. A user study demonstrates that the animation metaphors are intuitive, with the exception of animation ordering. More work is necessary to synchronise animations better. Overall our research demonstrates that sketched-based animations can be useful for applications requiring rapid prototyping containing a limited number of joint animations. Examples are the programming of household robots and the creation of simple animated scenes in education and social network applications.

Area 4 - Interactive Environments

Full Papers
Paper Nr: 47
Title:

HEAD TRACKING BASED AVATAR CONTROL FOR VIRTUAL ENVIRONMENT TEAMWORK TRAINING

Authors:

Stefan Marks

Abstract: Virtual environments (VE) are gaining in popularity and are increasingly used for teamwork training purposes, e.g., for medical teams. One shortcoming of modern VEs is that nonverbal communication channels, essential for teamwork, are not supported well. We address this issue by using an inexpensive webcam to track the user’s head. This tracking information is used to control the head movement of the user’s avatar, thereby conveying head gestures and adding a nonverbal communication channel. We conducted a user study investigating the influence of head tracking based avatar control on the perceived realism of the VE and on the performance of a surgical teamwork training scenario. Our results show that head tracking positively influences the perceived realism of the VE and the communication, but has no major influence on the training outcome.

Short Papers
Paper Nr: 9
Title:

AUGMENTED REALITY SYSTEM FOR KEYHOLE SURGERY - Performance and Accuracy Validation

Authors:

Juan José Fuertes, Fernando López-Mir, Valery Naranjo and Mario Ortega

Abstract: This work presents the performance and validation of an augmented reality (AR) system to help the surgeon for trocar placement in laparoscopic surgery. The virtual organs are obtained by taking previous computed tomography (CT) or magnetic resonance (MR) images of the patient and by applying segmentation methods. Once in the operating theater, a real-time image of the patient is captured with a regular camera that detects the patient’s pose (position + orientation) thanks to a marker that is centered on the navel. Then, 3D virtual organs are registered and fused with the real-time image, helping the surgeon to know the points, at where, to place the trocars. To validate the system’s accuracy and performance, a 3D jar-model is extracted from CT images which is then registered and fused with the real-time jar-image. An error of 2.91 millimeters is measured when the system accuracy is tested.

Paper Nr: 22
Title:

A NEW TERRAIN DATA COMPRESSION SCHEME FOR INTERACTIVE TERRAIN VISUALIZATION SYSTEMS

Authors:

Ricardo Olanda

Abstract: Over the last years, there has been a great development on real time terrain visualization applications using remote databases. One of the main problems that these applications must face is the storage and transmission of terrain data. Despite the considerable bandwidth increase of internet connection during last years, the large amount of data to be transmitted can easily saturate these connections. On other hand, since data must be stored in the client side, clients need a considerable storage space. In this context, we propose a new compression scheme that solves or minimizes these problems. It is based on JPEG2000 standard; however, the wavelet analysis and synthesis algorithms are modified to allow efficient transmission and reconstruction of terrain data by using tiled pyramids multiresolution techniques. A comparative study including current techniques shows that the proposed scheme obtains a better compression ratio of the terrain data, reducing the storage space and transmission bandwidth needed, achieving a better visual quality of terrain data reconstructed after data decompression.

Paper Nr: 34
Title:

AUTOMATIC MULTI-PROJECTOR CALIBRATION - A Review of Systems for Non-experienced Users

Authors:

Stefan Klose and Jérémie Gerhardt

Abstract: Multi-projector systems are widely used in many application areas. Such systems are for instance employed to increase the brightness or the resolution of projected images. Intrinsic to multi-projector systems are problems like geometric misalignment, especially when projecting onto complex arbitrarily formed projection surfaces, and photometric deviations. Therefore, several difficult calibration tasks (geometry, brightness, color) have to be performed. A high-quality and easy-to-use calibration process is the key to good usability for untrained or unexperienced users. Due to the fact that manual calibration is time-consuming and imprecise, automatic approaches were developed in recent years. This paper analyzes the most popular state-of-the-art algorithms and setups with respect to their advantages and disadvantages. We summarize the general working principles of calibration algorithms and provide an outlook into the fields in which the described algorithms are most useful.

Paper Nr: 39
Title:

VIEWPOINT SELECTION BY PAINTING

Authors:

Takashi Michikawa

Abstract: Complex 3D models are very time-consuming to render, and it is difficult to achieve the desired viewpoint for them using interactive methods such as virtual trackballs. This paper presents an intuitive method for computing good camera positions through a simple painting interface. Given a 3D scene, the user simply paints the region of interest (ROI) on the 2D screen, and the camera is repositioned to pan in on it. Since the computation uses depth buffers, it is independent of the complexity of the model; this makes it efficient for viewing complicated 3D models. Here, we also demonstrate several applications in 3D painting, sketching and light placement.

Paper Nr: 41
Title:

USER ENJOYMENT AND PERFORMANCE IN COLLABORATIVE AND COOPERATIVE GAMES IN SHARED 3D VIRTUAL ENVIRONMENTS

Authors:

Anastasiia Beznosyk and Peter Quax

Abstract: Increased interest in shared virtual environments has resulted in a necessity to investigate different factors that influence user interaction, both with the environment and other users. Introducing different types of joint activities into computer games can support a high level of realism and user engagement. This paper investigates two types of shared work: collaboration – where users individually perform actions in the environment towards a common goal, and cooperation – where users simultaneously act on the same objects in a shared environment. A basic computer game which requires joint work between all players was developed and used as a case study. We analyzed user performance and enjoyment in order to see which type of shared work is more preferable. Furthermore, the influence of user expertise on their enjoyment was also checked. From this particular study, we conclude that participants prefer cooperation over collaboration, as it provides more active and realistic performance. User expertise does not significantly influence enjoyment in this type of shared work, indicating that inexperienced players can enjoy the game equally as the experienced.

Paper Nr: 65
Title:

3D INTERACTIVE OBJECTS LAYOUT USING VIRTUAL REALITY TECHNIQUES AND CONSTRAINT PROGRAMMING

Authors:

Marouene Kefi

Abstract: Virtual Reality (VR) is a promising tool for effectively visualizing and interacting with objects and 3D environments. However, Virtual Environments (VEs) should provide some assistance to help the users in complex solving tasks. We aim to combine VR and Constraint Programming (CP) techniques in order to assist the users in realizing 3D objects layout in restricted spaces. The proposed approaches are based on a tight communication between a 3D rendering module and a highly efficient constraint solver. Layout modification are translated in incoming queries to the solver which generates the solutions that satisfy predefined constraints. In order to achieve users’ immersion in the VE and intuitive manipulation of the objects, a human-scale VE platform with haptic feedback is used. In this paper, we focus on the system architecture and we describe the implementation of simple constraints. Finally, some results based on geometric constraints are presented.

Posters
Paper Nr: 5
Title:

MODELLING AND OPTIMIZATION OF DATA-DRIVEN SCENE GRAPHS

Authors:

Sébastien Boisgérault and Eric Vecchié

Abstract: This article presents data-driven scene graphs, a set of models that address the needs of safety-critical user interfaces design. Data-driven scene graphs merge a description of the user interface behavior as a data-flow program with a description of its graphics content as a hierarchical structure of vector and raster elements. We present a formal description of these models, discuss their semantics and equivalence, and demonstrate that they are suitable for a class of rasterization optimizations based on selective pre-rendering.

Paper Nr: 46
Title:

AUTOMATED TUNING OF PARAMETERS FOR THE SEGMENTATION OF FREEHAND SKETCHES

Authors:

D. G. Fernández-Pacheco, F. Albert and N. Aleixos

Abstract: One of the main problems in the segmentation of freehand sketches is the difficulty of tuning the parameters involved in the process. Commonly, these parameters are chosen empirically from the observation of segmentation results in training sets. However, this approach rarely gets the best set of parameters, especially when the parameters depend on each other. This work presents an optimization algorithm, based on the simulated annealing technique, which tunes the segmentation parameters to improve segmentation results. The tuning of parameters has been formulated as an optimization problem where the cost function is expressed as the number of errors in the segmentation of a training set. Errors are determined comparing the computer segmentation with the correct one defined during the design of the shapes of the training set. Experimental work used 177 samples of 20 different shapes, achieving a performance ratio of 97.0% for the correct segmentation after tuning of parameters.

Paper Nr: 51
Title:

VIRTUAL EXHIBITION BUILDER

Authors:

Jorge Carvalho Gomes

Abstract: Virtual visits on the Web are an important means to publicize a museum collection and attract visitors. Software applications for building virtual exhibitions, in addition to being tools to create content for virtual visits, may help the staff of a museum to conceive and mount exhibitions. This paper presents the Virtual Exhibition Builder, an interactive software tool aimed at the creation of virtual exhibitions, given a 3D model of the exhibition space in an X3D file and a set of information about the artworks that are to be exposed. The development of this tool involves inputs proposed by museum experts.

Paper Nr: 56
Title:

EVALUATION OF 3D INTERACTION TECHNIQUES FOR GOOGLE EARTH EXPLORATION USING NINTENDO WII DEVICES

Authors:

Takehiko Yamaguchi

Abstract: We present a multi-modal virtual reality broadcasting system to support science education. This system is based on a web platform using Adobe Flash and enables users to explore Google Earth using the Nintendo Wii devices. The Google maps Flash API was used to control the user’s avatar. The Wii Remote was used for zooming and steering and the Wii Balance Board was used for walking. We tested operation workload for 9 different threshold angle combinations. We found a most low workload threshold angle combination of 45◦ (for zooming out) /-15◦ (for zooming in) and of 30◦ (for steering right) /-30◦ (for steering left). Moreover, we found overshoot range during actual operation.

Paper Nr: 61
Title:

HIGH-LEVEL SCENARIO EDITING FOR SERIOUS GAMES

Authors:

Casper van Est

Abstract: Although simulation games provide a competetive and safe alternative to real-life training sessions, the flexibility of adjusting such training sessions to fit the needs of individual trainees is relatively low. The reason for this is that these games are often delivered as a static product with predefined scenarios that cannot easily be edited by an instructor. This paper proposes a solution to this dilemma in the form of scenario editing, which allows instructors to define and edit scenarios, using high-level actions and events and some basic logic. A prototype scenario editing application was developed and subsequently evaluated, featuring a graph-metaphor for easily editing scenarios and an interface that allows real-time editing. The evaluation shows that the chosen approach is applicable and a good starting point for further development.

Paper Nr: 67
Title:

COMPUTER-AIDED AND VIRTUAL REALITY TECHNIQUES FOR GRAPHICAL ARTWORKS

Authors:

Héla Ben Mallem, Mickael Naud and Paul Richard

Abstract: Recent advances in computer graphics and 3D interaction devices raise new possibilities for artworks. However, extended analyses of the underlying technology as well as usability experiments have to be carried out. Moreover, 3D interaction techniques have to be proposed and evaluated. Another important aspect concerns the way computer technology may assist or support artistic creation. The objective of the work presented in this paper is to propose both a theoretical framework for the analysis of computer-aided artistic creation and 3D interaction techniques allowing user-centered artworks. Two immersive configurations along with 3D interaction techniques are proposed and analyzed. These interaction techniques are based on infrared cameras and 3D interaction devices such as a data-glove or the Nintendo WiimoteTM.

Area 5 - Social Agents in Computer Graphics

Posters
Paper Nr: 64
Title:

VIRTUAL REALITY AND AFFECTIVE COMPUTING TECHNIQUES FOR FACE-TO-FACE COMMUNICATION

Authors:

Hamzi Hamza and Paul Richard

Abstract: We present a multi-modal affective virtual environment (VE) for job interview training. The proposed platform aims to support real-time emotion-based simulations between an ECA and a human. The first goal is to train candidates (students, job hunters, etc.) to better master their emotional states and behavioral skills. The users’ emotional and behavior states will be assessed using different human-machine interfaces and biofeedback sensors. Collected data will be processed in real-time by a behavioral engine. A preliminary experiment was carried out to analyze the correspondence between the users’ perceived emotional states and the collected data. Participants were instructed to look at a series of sixty IAPS pictures and rate each picture on the following dimensions : joy, anger, surprise, disgust, fear and sadness.