WSCG '2003: Posters
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Item A formal framework approach for ray-scene intersection test improvement(UNION Agency, 2003) Revelles, J.; Lastra, M.; Montes, R.; Cano, P.; Skala, VáclavThe ray-scene intersection test is the most costly process when a scene is rendered. This process may be improved using any strategy to be able to speed-up it. Generally, any strategy used is based on the building of a spatial indexing in the scene domain or in the rays domain. However, there is no theory to formalize these techniques. In this paper, a formal framework approach for this technique is proposed.
Item Three-dimensional object recognition: statistical approach(UNION Agency, 2003) Abdul Salam, Rosalina; Rodrigues, Marcos Aurelio; Skala, VáclavThe design of a general purpose artificial vision system capable of recognizing arbitrarily complex three-dimensional objects without human intervention is still a challenging task in computer vision. Experiments have been conducted to test the ability of incorporating the knowledge of how human vision system works in a three-dimensional object recognition system. Firstly, the process of shape outline detection and secondly, the use of multiple viewpoints of object. Shape outline readings are put through normalization and dimensionality reduction process using an eigenvector based method to produce a new set of readings. Through statistical analysis, these readings together with other key measures, namely peak measures and distance measures, a robust classification and recognition process is achieved. Tests show that the suggested methods are able to automatically recognize three-dimensional objects from multiple viewpoints. Finally, experiments also demonstrate the system invariance to rotation, translation, scale, reflection and to a small degree of distortion.Item Classifying edges and faces as manifold or non-manifold elements in 4D orthogonal pseudo-polytopes(UNION Agency, 2003) Aguila, Ricardo Pérez; Ramírez, Antonio Aguilera; Skala, VáclavThis article presents our experimental results for classifying edges and faces as manifold or non-manifold elements in 4D Orthogonal Pseudo-Polytopes (4D-OPP's). For faces in 4D-OPP's we propose a condition to classify them as manifold or non-manifold. For the edges' analysis in 4D-OPP's we have developed two approaches: 1) The analogy between incident (manifold and non-manifold) edges to a vertex in 3D Orthogonal Pseudo-Polyhedra (3D-OPP's) with incident (manifold and non-manifold) faces to a edge in 4D-OPP's; and 2) The extension of the concept of "cones of faces" (which is applied for classifying a vertex in 3D-OPP's as manifold or non-manifold) to "hypercones of volumes" for classifying an edge as manifold or non-manifold in 4D-OPP's. Both approaches have provided the same results, which present that there are eight types of edges in 4D-OPP's. Finally, the generalizations for classifying the n-3 and the n-2 dimensional boundary elements for n-dimensional Orthogonal Pseudo-Polytopes as manifold or nonmanifold elements is also presented.Item A visualization-based approach to explore geographic metadata(UNION Agency, 2003) Albertoni, R.; Bertone, A.; De Martino, M.; Skala, VáclavThe paper presents a visualization-based approach to explore large databases of geographic metadata. The aim of the data exploration is to search and acquire expressive geographic data to create a geographic information system. Metadata repositories which provide information about available geographic data exist on the web and are usually queried to perform data acquisition task. We propose a visualization–based tool to assist the user in this metadata exploration. The approach is characterized by the integration of multi visualization techniques, interaction methods and data mining concepts. The use of multi visualization techniques and a dynamic interaction with them allow to discover new information among data and assists the user in his reasoning.Item Centerline computation and geometric analysis of branching tubular surfaces with application to blood vessel modeling(UNION Agency, 2003) Antiga, Luca; Ene-Iordache, Bogdan; Remuzzi, Andrea; Skala, VáclavIn this work we present a robust and accurate method for the computation of centerlines inside branching tubular objects starting from a piecewise linear representation of their boundary. The algorithm is based on solving the Eikonal equation on the Voronoi diagram embedded into the object, with wavefront speed inversely proportional to Voronoi ball radius values. As a result, provably accurate centerlines and maximal inscribed ball radius values along them are provided. In the same framework, a method for local surface characterization is also developed, allowing robust computation of the distance of surface points to centerlines and disclosing the relationship of surface points with centerlines. A new surface-based quantity is finally proposed, the normalized tangency deviation, which provides a scale-invariant criterion for surface characterization. The developed methods are applied to 3D models of vascular segments in the context of patient-specific anatomical characterization.Item Cˆambio: a realistic simulated robot for vision algorithms(UNION Agency, 2003) Aranha, Claus C.; Carvalho, Schubert L.; Gonçalvez, Luiz M. G.; Skala, VáclavWe introduce concepts and algorithms for control of visual motor commands and realistic simulation of basic abilities as visual servoing and perception for robotics vision simulation. We use the tools to build part of a humanoid (arms and head) robot, affectively named “Cˆambio”. We describe Cˆambio’s design, providing an overviewon the most used feature extraction techniques for perception, discussing implementation issues. We show the usefulness of a simulated platform as an inexpensive alternative for testing and developing computer vision algorithms in real-time robotics applications.Item Antipole clustering for fast texture synthesis(UNION Agency, 2003) Battiato, S.; Pulvirenti, A.; Reforgiato Recupero, D.; Skala, VáclavThis paper describes a new method for analysis/synthesis of textures using a non-parametric multi-resolution approach able to reproduce efficiently the generative stochastic process of a wide class of real texture images. This is realized through a new data structure the Antipole Tree and a suitable research strategy able to outperform both the classical linear full-search heuristic and the TSVQ (Tree Structure Vector Quantization) acceleration used in previous related works. Experimental results performed on an exhaustive set of textures [VisTex] show the effectiveness of the proposed approach.Item An efficient algorithm for codebook design in transform vector quantization(UNION Agency, 2003) Begum, Momotaz; Nahar, Nurun; Fatimah, Keneez; Hasan, M. K.; Rahman, M. A.; Skala, VáclavIn this paper, a new wavelet-domain codebook design algorithm is proposed for image coding. The method utilizes mean-squared error and variance based selection schemes for good clustering of data vectors in the training space. As the clustering process terminates only in two steps, it is highly computationally efficient as compared to other reported methods. Simulation results are presented to show the superior performance of the proposed method in terms of peak signal-to-noise ratio as compared to the standard Linde-Buzo-Gray algorithm for codebook design.Item Finding feasible parametr sets for shape from silhouettes with unknown position of the viewpoints(UNION Agency, 2003) Bottino, Andrea; Jaulin, Luc; Laurentini, Aldo; Skala, VáclavReconstructing 3D shapes from 2D silhouettes is a common technique in computer vision. It requires knowing the position of the viewpoints with respect to the object. But what can we say when this information is not available? This paper provides a first insight into the problem, introducing the problem of understanding 3D shapes from silhouettes when the relative positions of the viewpoints are unknown. In particular, the case of orthographic silhouettes with viewing directions parallel to the same plane is thoroughly discussed. Also we introduce sets of inequalities, which describe all the possible solution sets and a paving technique to calculate the feasible solution space of each set.Item A physical particle model of morphogenesis(UNION Agency, 2003) Boulenguez, Pierre; Luciani, Annie; Skala, VáclavThis paper describes an evolutionary process which produces dynamic biologic-like patterns. Simulation and visualization of the development of cell populations has many applications. For example, developmental biology and computer graphics. Physically-based particle models are efficient to simulate the dynamical behavior of real life objects. In this article, we propose to model the growth of a biologic tissue using sets of interacting physically-based particles to represent cells, which ad interact to form a tissue.Item Experimental system for visualisation of the light load(UNION Agency, 2003) Čadík, Martin; Slavík, Pavel; Přikryl, Jan; Skala, VáclavThis paper presents our work on an experimental system for visualisation of the light load. The light load is defined as the total amount of light radiation received by all areas of a 3D scene. The emphasis of the presented system lays on outdoor architectural scenes, but indoor scenes are handled as well. The aim of the system is to visualise the light load either in a single moment or integrated during a longer time period. We have selected a hierarchical Monte Carlo radiosity method to solve the specified problem. This method was extended to handle parallel light sources and specular reflections. New “lighting” iteration was added to computation phase to consider natural light sources such as Sun and sky. The system was implemented in Java programming language using the Java3D API. Thanks to this implementation environment, our system is flexible, easy to modify and extend and it is suitable for experimental and educational purposes.Item Navigation functionality for virtual archaeology(UNION Agency, 2003) Ferko, Andrej; Grabner, Markus; Schwann, Grabner; Sormann, Mario; Schindler, Konrad; Skala, VáclavThe paper reports the ongoing functional specification of a virtual archaeology system. Taking into account the goals of ISO standards MPEG-7 and SEDRIS, we have summarized methodologies from related IT fields (visualization, multimedia, HCI and VR) relevant for virtual archaeology system functionality. One part of the ideas has been used to specify the functionality of a particular system for immersively exploring the ancient Greek excavations model within the Studierstube virtual reality installation. In particular, the visualization scenarios, navigation modes and sound spaces complete functionalities were specified. The results contribute both to current methodology and future research findings.Item A fast algorithm for delaunay based surface reconstruction(UNION Agency, 2003) Gao, Shan; Lu, Han-Qing; Skala, VáclavAdvanced 3D scanning technologies enable us to obtain dense and accurate surface sample point sets. From sufficiently dense sample point set, Crust algorithm, which is based on Voronoi diagram and its dual Delaunay triangulation, can reconstruct a triangle mesh that is topologically valid and convergent to the original surface. However, the algorithm is restricted in the practical application because of its long running time. Based on the fact that we do not need dense sample in featureless area for successful reconstruction, we propose a nonuniformly sampling method to resample the input data set according to the local feature size before reconstruction. In this way, we increase the speed of reconstruction without losing the details we need.Item Sign-language synthesis for mobile environments(UNION Agency, 2003) Igi, Seiji; Tamaru, Mitsue; Yamamoto, Yasunori; Ujitani, Megumu; Sugita, Shigeharu; Skala, VáclavThis paper describes the synthesis of sign-language animation for mobile environments. Sign language is synthesized by using either the motion-capture or motion-primitive method. An editing system can add facial expressions, mouth shapes and gestures to the sign-language CG animation. Sign-language animation is displayed on PDA screens to inform the user of his/her mobile environment.Item A procedural model for interactive animation of breaking ocean waves(UNION Agency, 2003) Jeschke, Stefan; Birkholz, Hermann; Schmann, Heidrun; Skala, VáclavThis paper presents a procedural model for breaking ocean waves that is intended to be used for interactive visualization. The movement as well as the appearance of the waves is modelled by a set of functions in dependence of time and space. This continuous surface description allowes it to calculate all properties of every point (including foam) on the ocean surface at every time without any information from previous time steps. By using an adaptive sampling sheme for rendering, the frame rate of the animation only depends on the screen resolution rather than on the model size. The model is quite simple, easy to implement, fast to compute and provides a visual appealing interactive animation of infinite large ocean coast scenes. On the other hand it provides only limited flexibility due to its procedural character. For achieving more realistic scene appearance, it may also easily be combined with models for deep-water waves presented in the past.Item Use of hybrid rendering styles for presentation(UNION Agency, 2003) Jesse, Rolland; Isenberg, Tobias; Skala, VáclavThis paper presents hybrid rendering that combines the use of photorealistic and non-photorealistic rendering styles in the same image. This allows to extend the set of expression dimensions available in a visualization environment. To provide general applicability, this use of hybrid rendering styles is controlled by an XML-based scene description. We discuss the according schema definition and present an architecture for implementing the presented methods as well as two exemplary applications.Item Improved gradient estimation methods for rendering of volume data(UNION Agency, 2003) Ježek, Bruno; Antoš, Karel; Skala, VáclavThe paper presents two methods that improve gradient estimation in 3D voxel space. The gradient estimation is an important step in the rendering and shading process to obtain realistic and smooth final images of visualized objects. The most used gradient estimation methods, gray-level gradient methods, Z-buffer gradient methods and binary gradient methods in some cases produce artifacts that appear as dark areas and staircase structures in a final image. To deal with the problem, two new methods for gradient estimation are suggested, the reverse gradient method and the angle difference method. The new methods were tested and compared with other gradient estimation methods. Measurements, which have been made on both the data and image levels, have shown that both developed methods improve the quality of volume data rendering.Item Fast algorithm for stochastic tree computation(UNION Agency, 2003) Kang, MengZheng; Reffye, Philippe de; Barczi, Jean-François; Hu, Bao Gang; Skala, VáclavIn this paper, a recursive algorithm that can build complex tree structure quickly is presented briefly. The plant structural growth is based on a dual-scale automaton, in which ‘macrostate’ and ‘microstate’ are used to simulate the growth unit and the metamers inside growth unit separately. Each state is characterized by its ‘physiological age’. The automaton is non-deterministic in case that the probabilities exist in each growth cycle simulating the bud activity. Since the main plant structure and branches are statistically similar, and each structure can be decomposed into an axis and substructures, simulation is begun from smallest structures that have no further branch, and that information are used when such kind of structures appear in other branches. To keep the diversity of tree structure, several stochastic structures will be simulated at one time for a given physiological and chronological age. This algorithm can save a lot of time compared to node-by-node simulation. Verification is done both in organ number counting and visualization.Item Bi-directional rays in global illumination(UNION Agency, 2003) Kelemen, Csaba; Benedek, Balász; Szirmay-Kalos, László; Szécsi, László; Skala, VáclavGlobal illumination algorithms use rays to transfer the light in the scene. A ray connects two points that are mutually visible from each other. Although it seems intuitive to transfer the light into both directions along the ray, only a few algorithms have taken advantage of bi-directional rays so far, which can increase the samples for minimal additional cost. In this paper we propose a non-diffuse global illumination algorithm that exploits this promising alternative. The algorithm is easy to implement but robust and is able to render complex scenes within a few tens of second.Item Computing subdivision surface intersection(UNION Agency, 2003) Lanquetin, S.; Foufou, S.; Kheddouci, H.; Neveu, M.; Skala, VáclavComputer surface intersections is fundamental problem in geometric modeling. Any Boolean operation can be seen as an intersection calculation followed by a selection of parts necessary for building the surface of the resulting object. This paper deals with the computing of intersection curveson subdivision surfaces (surfaces generated by the Loop scheme). We present three variants of our algorithm. The first variant calculates this intersection after classification of the object faces into intersecting and non-intersecting pairs of faces. the second variant is based on 1-neighborhood of the intersecting faces. The third variant uses the concept of bipartite graph.
