WSCG '2003: Short papers
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Item Constructing approximate voronoi diagrams from digital images of generalized polygons and circular objects(UNION Agency, 2003) Roque, Waldir L.; Doering, Dionísio; Skala, VáclavIn this paper we present the geometrical construction of an approximate generalized Voronoi diagram for generalized polygons and circular objects based on their minimum geometrical structure that are extracted from the object's digital image. The construction is done in O(n) time complexity, where n is the number of single points defining the set of objects. An application of this technique has been done for mobile robot path planning.
Item Mesh simplification based on shading chracteristics(UNION Agency, 2003) Zhang, Hui; Shu, Huazhong; Luo, Limin; Skala, VáclavMesh simplification is a key research area in scientific visualization and virtual reality. The paper presents a new method of polyhedral model simplification based on vision characteristic and edge collapse. This method determines model's vision characteristic by computing the maximum product of angle between normal of vertex and adjacent triangles with area of these triangles. It can achieve a high decimation rate, while keeping the details of vision. This algorithm can also be extended to triangle decimation criterion easily.Item Hardware architecture for fast camera effects(UNION Agency, 2003) Szijárto, Gábor; Skala, VáclavCurrent commercial graphics cards do not offer fast enough special hardware to render camera effects like motion blur or depth of field. Even the pixel shader, which is useful in many rendering algorithms, is unable to support these effects. This paper presents a hardware structure, which provides fast rendering capability for realizing filtering effects, including also depth of field and motion blur.Item Towards feature-based building reconstruction from images(UNION Agency, 2003) Schindler, Konrad; Bauer, Joachim; Skala, VáclavThis paper presents a feature-based approach to piecewise planar modeling of architectural scenes from an oriented image sequence. An improved line detection algorithm is presented, which uses vanishing points to detect lines in the images and reconstruct them in 3D. Subsequently an extension of the 3D Hough transform is presented which allows efficient and robust detection of planes in a set of 3D lines. The detected planes and a dense point-set are used to reconstruct a piecewise planar building model. The presented techniques are demonstrated on a real-world dataset.Item Smart objects for attentive agents(UNION Agency, 2003) Peters, Christopher; Dobbyn, Simon; Nameee, Brian Mac; O'Sullivan, Carol; Skala, VáclavWe present an extended framework for modelling agent-object interactions in virtual environments. Our framework is based on the concept of Smart Objects and provides agents with pre-programmed interaction information for the automatic generation of animations. The ability to generate such animations without human intervention is vital when constructing plausible, real-time agents. Unlike previous approaches, our model also contains information for directing the attention of agents when interacting with objects. Such information is useful for driving gaze behaviours, for example when grasping objects. Our framework supports both bottom-up (attention capture) and top-down, task driven, simulation of behavioural animation on a per-object basis. It also provides support for the management of the interactions of multiple agents with a single object. We show how objects are designed and provide a concrete example of using the modelling approach with a gaze controller in an animation system.Item Camera self-calibration in underwater environment(UNION Agency, 2003) Pessel, Nathalie; Opderbecke, Jan; Aldon, Marie-José; Skala, VáclavThis paper presents a self-calibration technique for a camera mounted on an underwater vehicle designed to perform the 3D reconstruction of underwater scenes. Our aim is to identify the intrinsic parameters of the camera with methods that are adapted to the operational constraints on Ifremer’s underwater vehicles. The optical system is composed by a single vertical camera located below the underwater vehicle and looking downwards. The motion of the vehicle can be measured through navigation sensors and the observed 3D scene is always unknown. The use of a moving camera is not an obstacle for the application of stereoscopic methods. Nevertheless, the camera motion enables the use of robust algorithms for points matching, but impoverishes perspective effects between several images. Therefore, we are interested in the analysis of the conditions in which the procedure of self-calibration is valid and reliable, i.e.: the 3D characteristics of the scene and the camera motion. This paper presents the steps necessary for the camera self-calibration in an underwater environment: the extraction and the tracking of features in several successive images, the fundamental matrix estimation and the intrinsic parameters identification. Several tests and results are presented.Item Comparisom of accelerating techniques for discontinuity meshing(UNION Agency, 2003) Nechvíle, Karel; Tobola, Petr; Sochor, Jiří; Skala, VáclavCreating an appropriate mesh is one of demanding tasks of many global illumination algorithms. Discontinuity meshing proved to diminish artifacts caused by other meshing strategies. Since naive discontinuity meshing would produce a great amount of geometric computations, accelerating techniques are usually involved. In this paper, we present results obtained with help of k -discrete orientation polytopes ( k -DOPs) and oriented bounding boxes (OBBs) and compare them to previously used accelerating schemes like voxels, BSP-trees and octrees.Item Usingregistration, calibration, and robotics to build a more accurate virtual reality simulation for astronaut training and telemedicine(UNION Agency, 2003) Menon, Anil S.; Barnes, Bobby; Mills, Rose; Bruyns, Cynthia D.; Twombly, Alexander; Smith, Jeff; Montgomery, Kevin; Boyle, Richard; Skala, VáclavComputer simulation of surgery and scientific experiments help in preparation, training, and assessment. These benefits can be further extended with the integration of robotics for teleoperation and assistance. We describe our efforts to build a realistic and useable simulation for astronaut training and experiment planning. Most of our develop ment focused on user interaction with hand sensors, a necessary component for realism. For the hands, we developed a simulation and focused on aspects of fine tuning the registration and calibration to increase realism and functionality. This proved to b e a necessary basis to integrate robotics and further the simulation’s range of applications. Accurate registration, calibration, and robotic integration helped build a foundation for a useable simulation for astronaut training on ground and avenues of ro botic assistance during flight.Item Rock Image Classification Using Non-Homogenous Textures and Spectral Imaging(UNION Agency, 2003) Lepistö, Leena; Kunttu, Iivari; Autio, Jorma; Visa, Ari; Skala, VáclavTexture analysis and classification are usual tasks in pattern recognition. Rock texture is a demanding classification task, because the texture is often non-hom ogenous. In this paper, we introduce a rock texture classification method, which is based on textural and spectral features of the rock. The spectral features are considered as some color parameters whereas the textural features are calculated from the co-occurrence matrix. In this classification method, non-homogenous texture imag es are divided into blocks. The feature values are calculated for each block separately. In this way, the feature values of the texture image can be presented as a feature histogram. The classification method is tested using two types of rock textures. The experimental results show that the proposed features are able to distinguish rock textures quite well.Item Simulating Deformable Tools with Haptic Feedback in a Virtual Environment(UNION Agency, 2003) Laycock, S. D.; Day, A. M.; Skala, VáclavSimulations for training and analysis incorporating haptic feedback are becoming more popular and the sophistication of these simulations is increasing. Many systems now allow a range of simulated rigid tools to be used in haptic feedback applications, such as scalpels in surgical simulations. However, very often the rigid property of the simulated tool does not correspond to the flexibility of the tool in the real world. This paper aims to show how deformable tools can be used in conjunction with haptic feedback to improve realistic interactive simulations. The work shows how a finite element model of a beam can be used to simulate a three dimensional deformable rod in a virtual environment. The ability to perform the collision detection, force responses and update the physical model at a suitable haptic rate is a crucial requirement. An approximation to the finite element method is illustrated which allows more time, per frame, to be allocated to the collision detection without noticeably degrading the physical model.Item Real Time Skin Deformation with Bones Blending(UNION Agency, 2003) Kavan, Ladislav; Žára, Jiří; Skala, VáclavSkeletal animation with vertex blending is a popular method to model believable 3D characters. Its main advantage is its speed that allows real-time deformation even on low-level hardware. However it has some drawbacks as well: for some movements it produces non-natural postures like twisting elbows. We present a new method called bones blending that can be used as an alternative to vertex blending. Bones blending has a power to overcome the artifacts of vertex blending.Item A Quantitative Analysis of Culling Techniques for Real-time Rendering of Digital Elevation Models(UNION Agency, 2003) Hesse, Michael; Gavrilova, Marina; Skala, VáclavThe paper is concerned with investigation of effects of culling techniques on quality and smoothness of terrain data visualization within a 3D interactive environment. We utilize the Real-Time Optimally Adapting Mesh (ROAM) approach, extended with a number of efficient techniques such as implicit coordinates method within the patch array representing ROAM and the viewpoint dependent triangle rendering method for dynamic level of detail (LOD) updates. The method, which allows dynamic and interactive first person view, is combined with the View Frustum culling, the Backface culling and an original Relational Position Culling. Standard error metrics are used to verify the rendering consistency. The experimentation is conducted on two data sets representing simple gradual contour changes (Susanville, California) and complex steep contour changes (Kluane National Park, USA). Based on the results, applicability of each of the culling techniques to terrain model is discussed.Item Shading vy Spherical lienear interpolation using de moivre's formula(UNION Agency, 2003) Hast, Anders; Barrera, Tony; Bengtsson, Ewert; Skala, VáclavIn the classical shading algorithm according to Phong, the normal is interpolated across the scanline, requiring a computationally expensive normalization in the inner loop. In the simplified and faster method by Gouraud, the intensity is interpolated instead, leading to faster but less accurate shading. In this paper we use a third way of doing the interpolation, namely spherical linear interpolation of the normals across the scanline. This has been explored before, however, the shading computation requires the evaluation of a cosine in the inner loop and this is too expensive to be efficient. By reformulating the original approach in a suitable way, De Moivre’s formula can be used directly for computing the intensity so that no normalization is needed. Hence, no trigonometric functions, divisions or square roots are necessary to compute in the inner loop. Unfortunately the setup for each scanline will be rather slow unless some efficient reformulation of the necessary trigonometric calculations can be found. We suggest this problem for future research.Item Efficient image-based projective mapping using the master texture space encoding(UNION Agency, 2003) Guinnip, David; Rice, David; Jaynes, Christopher; Stevens, Randall; Skala, VáclavWe introduce an encoding technique that supports efficient view-dependent image-based rendering applications that combine photorealistic images with an underlying surface mesh. The representation increases rendering efficiency, reduces the space required to store large numbers of object views, and supports direct image-based editing for realistic object manipulation. The Master Texture Space encoding transforms an original set of exemplar images into a set of Master Textures that share a globally consistent set of texture coordinates based on underlying object geometry and independent of camera positions used to create the exemplar views. An important property of the master texture space is that an arbitrary but fixed pixel position in all the Master Textures correspond to the same point on the object surface. This property increases rendering efficiency for real-time dynamic image-based rendering applications because new texture coordinates do not have to be loaded as a function of viewpoint. In addition, changes in a Master Texture image can be rapidly propagated to all views to add/remove features, generate new viewpoints, and remove artifacts to a pre-existing image-based scene. Results presented here demonstrate that the technique reduces real-time rendering rates by 1.6 milliseconds per frame for reasonably complex models on a commodity graphics card. Two example scenarios demonstrate how the Master Texture encoding supports efficient update of an image-based model.Item Real-time animation of underbrush(UNION Agency, 2003) Endo, Luis Carlos Yano; Morimoto, Carlos Hitoshi; Fabris, Antonio Elias; Skala, VáclavModeling natural phenomena is a problem that has been studied for a long time in Computer Graphics. A problem that currently arises is how to render and animate realistically natural phenomena in real-time. This paper presents a technique to model underbrush with fast and realistic animation. Pre-computations and a simplified physically based model were developed to achieve the work’s proposal.Item Storytelling in Collaborative Augmented Reality Environments(UNION Agency, 2003) Braun, Norbert; Skala, VáclavWe describe the several possibilities of using storytelling in an Augmented Reality Environment to support the collaborative experience of the users in those environments. We start with the motivation of a lack of storytelling and experience in CVEs. As an implication of the need for such experiences, we give a general definition of Interactive Storytelling and offer some insights on the difference between Interactive Stories and Games. We introduce our approach to Interactive Storytelling as a combination of Audience Participatory Theatre and a morphological approach to storytelling in Augmented Reality Environments. An overview of the technical development of the approach is followed by a project description, using the stated approach to verify the useful application of the approach in regard to collaborative user experiences.Item Optimizing parameters of a motion detection system by means of a genetic algorithm(UNION Agency, 2003) Bevilacqua, Alessandro; Skala, VáclavVisual surveillance and monitoring have aroused interest in the computer video community for many years. The main task of these applications is to identify (and track) moving targets. The traffic monitoring application we have developed requires that a large number of parameters is tuned in order to work properly. About thirty parameters concerning the detection algorithm have been c onsidered as to be optimized. Accordingly, this paper shows how a Genetic Algorithm (GA) represents a powerful task in order to automatically compute sub-optimal parameter settings in a motion detection system. Besides, to our knowledge this work is the first attempt of using GAs to such a problem. Accurate experiments accomplis hed on a challenging test se quence show the relevant results attained in terms of qualitative performance.Item Grid Method Classification of Islamic Geometric Patterns(UNION Agency, 2003) Aljamali, Ahmad M.; Banissi, Ebad; Skala, VáclavThis paper proposes a rational classification of Islamic Geometric Patterns (IGP) based on the Minimum Number of Grids (MNG) and Lowest Geometric Shape (LGS) used in the construction of the symmetric elements. The existing classification of repeating patterns by their symmetric groups is in many cases not appropriate or prudent [Joy97]. The symmetry group theories do not relate to the way of thinking of the artisans involved, and completely has ignored the attributes of the unit pattern and has focused exclusively on arrangement formats. The paper considers the current symmetric group theories only as arrangement patterns and not as classifications of IGP since they have a “global approach” and have failed to explore the possibilities in the construction elements of IGP. The Star, a central Rosette, which is the most important element of IGP, forms the core of our study. The paper proposes new nomenclature to be used in the description of the unit pattern based on the MNG and LGS used in the construction of a Star/Rosette pattern that can be used to achieve the final design. We describe and demonstrate procedures for constructing Star/Rosette unit patterns based on our proposed classification in a grid formation dictated by the final design of the unit pattern.Item Combined Partial Motion Clips(UNION Agency, 2003) Al-Ghreimil, Nadia; Hahn, James K.; Skala, VáclavWe present a motion editing method for articulated figures using Combined Partial Motion Clips (CPMCs). CPMCs contain detailed motion information for some parts of the articulated figure. They can be used to edit base motions in such a way that the parts that are not defined in detail will still be affected thereby emulating the correlation that exists naturally between joint movements. This is achieved through the inclusion of equations in the CPMC that capture the effects of the detailed motion on other degrees of freedom of the articulated figure.Item Directionally dependent light sources(UNION Agency, 2003) Albin, Stéphane; Péroche, Bernard; Skala, VáclavThis paper deals with light sources in computer graphics. Different kinds of light sources and different types of solutions generally used are first described. Then, a new solution for directionally dependent light sources based on No\'e and P\'eroche's model\cite{Noe00-HRBLS*} is proposed to avoid drawbacks of bilinear interpolation. The use of singular integrals with locally supported functions allows a fast and accurate reconstruction of goniometric diagrams. Application to point light sources is finally compared with some experimental results.
