WSCG '2002: Short Communication Papers

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http://hdl.handle.net/11025/6028

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Showing 1 - 20 out of 22 results

Multicomputer system dedal-2 for local landscape monitoring
(UNION Agency, 2002) Gribkov, I. V.; Koltsov, N. V.; Kotovich, N. V.; Kravchenko, A. A.; Kutsaev, A. S.; Nikolaev, V. K.; Zakharov, A. V.; Skala, Václav
The paper contains the description of a multicomputer system for terrestrial surface automatized monitoring. The system is able to detect moving objects on the terrain considered, to locate static objects which appear/disappear on terrain as well as to recognize such objects. The system uses photosnapshot the terrain and a set of reference images for recognition.
Computer-aided detection and segmentation of objects on medical images
(UNION Agency, 2002) Belikova, Tatjana; Plenichka, Roman; Ivasenko, Iryna; Skala, Václav
Series of methods for improved detecting and segmenting objects, situated on a complex background, have been developed. Model-based detection was applied for automatic detection and segmentation of the objects of interest on initial images and images after optimal filtering. The optimal linear filter was used to improve imaging of the object (its details and margin) on the observed image. Filtering of small-size details to improve false alarm and misdetection rates then followed the segmentation procedure. Developed series of methods were tested on test images and real medical images (lung tomograms) with small solitary nodules. A comparison of segmentation results obtained before and after optimal filtering showed that optimal filtering allows to outline the object region on medical images better and helps to identify more precisely the object margin. The developed series of methods can be useful for computer-assisted detection, segmentation, and analysis of low contrast flaws (lesions) on a complex image background that is important for solving of numerous medical tasks and for technical tasks of material inspection.
Prefetching policies for remote walkthroughts
(UNION Agency, 2002) Zach, Christopher; Karner, Konrad; Skala, Václav
We present a 3D data streaming approach for remote walkthroughs, that integrates local optimization techniques for realtime rendering with prefetching techniques for remote scene graphs. Especially culling methods, that don't possess frame to frame coherence, can successfully be combined with remote scene databases, if the prefetching algorithm is adapted accordingly. We present a quantitative transmission policy, that takes the limited bandwidth of the network and the limited memory available at the client computer into account.
Fast algorithms of plant computation based on substructure instances
(UNION Agency, 2002) Yan, Hong-Ping; Barczi, Jean Francois; De Reffye, Phillipe; Hu, Bao-Gang; Skala, Václav
Fast rendering and botanically faithful description of plants are a real challenge in computer graphics. Usually, plant production is computed using the method internode by internode, while there exist a lot of buds in an individual tree, therefore, this approach is quite time-consuming even for a medium-size tree. In this paper, we present a new algorithm based on substructure instances to quickly compute plants’ production, and then, for certain plant architectural models, combine with the geometrical rules to create a substructure library. Finally, we construct 3D virtual plants using 3D organs. Compared with the classical method in computing and constructing plant structures, the algorithm described in this paper is much faster while keeping botanical nature of plant. The algorithm can be generalized to most plant species.
Simulating virtual character's learning behavior as an evolutionary process using genetic algorithms
(UNION Agency, 2002) Wan, Tao Ruan; Tang, Wen; Skala, Václav
In this paper, we describe a genetic algorithm approach to simulate complex virtual character's learning behaviours as an evolutionary process. The method presented here enables virtual character to have abilities to learn for specific assigned tasks. The skill for the task can be developed and evolved through the experiences of performing the task. The animation system presented here has two tightly coupled simulation units, which are an artificial brain unit for learning and controlling and a physics-based motion simulation unit driven by simulated muscle forces.
Objects recognition by means of projective invariants considering corner-points
(UNION Agency, 2002) Vicente, M. A.; Gil, P.; Reinoso, O.; Torres, F.; Skala, Václav
This paper presents an object recognition technique based on projective geometry for industrial pieces that satisfy geometric properties. First at all, we consider some methods of corner detection which are useful for the extraction of interest points in digital images. For object recognition by means of projective invariants, an excessive number of points to be processed supposes a greater complexity of the algorithm We present a method that allows to reduce the points extracted by different corner detection techniques, based on the elimination of non-significant points, using the estimation of the straight lines that contain those points. Secondly, these groups of points are then used to build projective invariants which allow us to distinguish one object from another. Experiments with different pieces and real images in grey-scale show the validity of this approach.
Vector field metrics based on distance measures of first order critical points
(UNION Agency, 2002) Theisel, H.; Weinkauf, T.; Skala, Václav
Topological methods have been proven to be useful both for the visualization and the definition of distance measures of vector fields. This paper introduces and assesses a new distance measure for first order critical points of 2D vector fields. This distance measure forms the foundation of the definition of vector field metrics. Based on this we give an advanced and complete classification of all first order critical points.
Scan converting spirals
(UNION Agency, 2002) Taponeco, Francesca; Alexa, Marc; Skala, Václav
Scan-conversion of Archimedes' spiral (a straight line in polar coordinates) is investigated. It is shown that an exact algorithm requires transcendental functions and, thus, cannot have a fast and exact integer implementation. Piecewise polynomial approximations are discussed and a simple algorithm based on piecewise circular approximation is derived. Variations of the algorithms allow to scan convert other types of spirals.
The Multi-LDI: an image based rendering approach for interaction navigation, and visualization in complex virtual environments
(UNION Agency, 2002) Stoev, Stanislav L.; Peter, Ingmar; Strasser, Wolfgang; Skala, Václav
In this paper, we present a new data structure for image-based rendering: the multi LDI. The multi LDI consists of a number of Layered Depth Images (LDI) covering a hemisphere of possible viewing angles. It allows compact image-based storage and fast rendering of large and complex scenes, while supporting rendering from large range of viewing directions. Since the internal occlusion in each LDI is very small, and only one of the LDIs in the multi LDI is rendered at a time, the rendering cost is significantly reduced compared to geometry-based rendering and even compared to other image-based rendering methods. Moreover, the single LDIs in the multi LDI can be generated on demand using a number of depth images rendered with an offscreen renderer. We also discuss a comparison of the geometry-based rendering and our image-based method and present some measured rendering times. Furthermore, we describe the utilization of this technique in a complex Virtual Environment (VE) for realizing navigation, visualization, and interaction aids. In particular, we present a multiple viewport technique providing two important features: (1) A sort of history during the modeling process, whereas a live 3D copy of the scene is displayed in a window in front of the user. (2) Different live views of the scene, seen from arbitrary viewpoints, in order to display details occluded in the normal view.
Interactive information visualization of entity-relationship-data
(UNION Agency, 2002) Rieger, Thomas; Taponeco, Francesca; Skala, Václav
This work presents methods for interactive analysis of unknown data and relations. It supports the selection of relevant parts of the data and the visualization of relations using different layout strategies for 2d visualizations and for 3d visualizations. Moreover, the user can select additional mappings to display extra information, with the help of supplementary visual variables in an easy way. Hereby the user can interactively create new visualizations and new sights and sift through the data in order to reveal discrepancies, to uncover trends or to provide vital operational insights.
Real-time recursive specular reflections on planar and rurved surfaces using graphics hardware
(UNION Agency, 2002) Nielsen, Kasper Høy; Christensen, Niels Jørgen; Skala, Václav
Real-time rendering of recursive reflections have previously been done using different techniques. However, a fast unified approach for capturing recursive reflections on both planar and curved surfaces, as well as glossy reflections and interreflections between such primitives, have not been described. This paper describes a framework for efficient simulation of recursive specular reflections in scenes containing both planar and curved surfaces. We describe and compare two methods that utilize texture mapping and environment mapping, while having reasonable memory requirements. The methods are texture-based to allow for the simulation of glossy reflections using image-filtering. We show that the methods can render recursive reflections in static and dynamic scenes in real-time on current consumer graphics hardware. The methods make it possible to obtain a realism close to ray traced images at interactive frame rates.
Measuring isotropic local contrast: a circular mask based approach
(UNION Agency, 2002) Montrucchio, B.; Lamberti, F.; Sanna, A.; Montuschi, P.; Skala, Václav
Many image processing tasks depend on contrast measures, which can be used to compare and improve contrast enhancement algorithms. Contrast definitions are not always suitable for all situations. In particular an isotropic local contrast measure, that produces a flat response to sinusoidal gratings, can be difficult to obtain. In this paper we review the main existing contrast measures, and propose a new approach, denoted as Circular Mask Metric (CMM). It is based on band-pass filters and circular mask based local contrast computations. This approach has been applied on different test images and with three contrast enhancement methods, in order to show its potentialities for contrast enhancement algorithm testing and improving.
A multi-scale approach to corner tracking
(UNION Agency, 2002) Mohanna, Farahnaz; Mokhtarin, Farzin; Skala, Václav
This paper presents a multi-scale corner tracking algorithm based on a multi-scale corner detector. To extract corners from each frame of video sequences, the enhanced CSS corner detector using different scales of smoothing is applied. In the matching stage two-frame correspondence combined with three-frame based monitoring is considered. We monitor tracked corners from the third frame of input sequence in matching stage. Proposed three-frame monitoring helps to ensure that the number of tracked corners and their tracked positions among frames become more robust. Since the proposed corner tracker has enough robust corners based on multi-scale corner detector, it is practical and efficient. In matching stage, among similarity functions, standard cross-correlation, zero-mean cross-correlation, sum of squared differences, and x2-test measurements are tested. Well-known real video databases depicting translation, scaling, rotation and affine transformation with different lighting and different camera motions are used as experiments. All experiments confirm that the performance of the proposed tracker is high and reliable due to monitoring matched corners among frames.
Free form shape representation using nurbs modeling
(UNION Agency, 2002) Liang, Kim Meng; Rajeswari, Mandava; Khoo, Bee Ee; Skala, Václav
The representation, matching and analysis of objects of interest are of prime importance in shape-based retrieval systems. Considering that these systems involve analysis of various complex shapes, an accurate representation of free form shape is required. A simple and accurate shape representation procedure would ensure meaningful results from the shape-based retrieval systems. Motivated by this factor, this paper presents a free form shape representation technique using Non-Uniform Rational B-Spline (NURBS) modelling. The free form shapes are modelled using control points and weights. NURBS posses attractive properties such as spatial uniqueness, bounded and continuous, local shape controllability and shape invariance under transformation. Furthermore, NURBS based shape descriptor allows accurate reconstruction of the shape boundary from the NURBS features used to describe it. This paper presents the details of deriving a set of NURBS features using the boundary of the object. The accuracy and data reduction properties using NURBS are examined by carrying out an experiment on two sets of images: geometric and free form. Accuracy of the representation is evaluated by using centroid-radii error function, which computes the cumulative distance between the intersection points by radii lines on the boundary of the original image and the reconstructed image. The data reduction property is shown by the ratio computation between the number of control points and the boundary points. The overall experiment results show that NURBS is an accurate shape descriptor and a potential candidate for use in shape-based image retrieval systems.
Fast algorithm for creating image-based stereo images
(UNION Agency, 2002) Kozankiewicz, Przemysław; Skala, Václav
The process that creates stereo images typically takes from 1.5 to 2 times longer than the algorithm for mono images. This paper presents a fast image-based algorithm for computing stereo images, that needs a little more time than the algorithm for mono images. The presented algorithm uses a single image with depth information (e.g. z-buffer) as an input and produces two images for left and right eye. This algorithm is a simplification of the 3D warping algorithm.
Stylized silhouette rendering using progressive meshes
(UNION Agency, 2002) Kim, Sung-Soo; Choe, Seung-Keol; Skala, Václav
Silhouette information has been used to enhance artistic rendering of 3D objects.We present a new method for progressive silhouette rendering of triangle mesh of arbitrary topology by using parameterized brush functions in various styles. The proposed progressive silhouette rendering framework is consist of two major steps; one is mesh simplification for silhouette feature preservation and the other is the stylized silhouette edge rendering. We also improve the mesh simplification algorithm that can preserve silhouette and volume of arbitrary mesh for silhouette rendering. First, for a given mesh, we can obtain progressive mesh(PM) through our proposed mesh simplification algorithm at the preprocessing step. Then, we can render silhouette edges by various kinds of effects progressively by performing the refinement of a given PM from a base mesh. Results demonstrate that progressive silhouette rendering which use the progressive mesh and brush functions can cause effect that a person sketches an arbitrary object gradually.
Real-time visualization of clouds
(UNION Agency, 2002) Heinzleiter, Paul; Kurka, Gerhard; Volkert, Jens; Skala, Václav
Rendering realistic cloud images is a challenging computational intensive task. The high computational demand makes physics-based on-the-fly rendering impossible for real-time applications on low-cost workstations. We present an approach to overcome this problem by using alpha-blended billboard textures. During a pre-processing step a series of pre-calculated images is generated for each cloud object of the scene. The images are showing each cloud object from different view points. For a given camera position on the ground the final cloud depiction is composed by an appropriate subset of alpha-blended images, assigned to billboard textures. In so doing, we are able to create a smooth transition between arbitrary camera positions on the ground.
Interactive visualization of volumetric vector fields using texture based particles
(UNION Agency, 2002) Guthe, Stefan; Gumhold, Stefan; Straßer, Wolfgang; Skala, Václav
This paper introduces a new approach to the visualization of volumetric vector fields with an adaptive distribution of animated particles that show properties of the underlying steady flow. The shape of the particles illustrates the direction of the vector field in a natural way. The particles are transported along streamlines and their velocity reflects the local magnitude of the vector field. Further physical quantities of the underlying flow can be mapped to the emissive color, the transparency and the length of the particles. A major effort has been made to achieve interactive frame rates for the animation of a large number of particles while minimizing the error of the computed streamlines. There are three main advantages of the new method. Firstly, the animation of the particles diminishes the inherent occlusion problem of volumetric vector field visualization, as the human eye can trace an animated particle even if it is highly occluded. The second advantage is the variable resolution of the visualization method. More particles are distributed in regions of interest. We present a method to automatically adjust the resolution to features of the vector field. Finally, our method is scalable to the computational and rasterization power of the visualization system by simply adjusting the number of visualized particles.
Dynamic visualization of the combustion processes in boilers
(UNION Agency, 2002) Gayer, Marek; Hrdlička, František; Slavík, Pavel; Skala, Václav
This paper focuses on the simulation and visualisation of coal combustion in the pulverised coal boilers. It is important to find optimal boiler configurations (both for the ecological and economical reasons), determine appropriate combustibles, optimize process of combustion, etc. These tasks are typically solved using traditional Computational Fluid Dynamics (CFD) methods that are in general computationally very expensive. Our work is based on a different approach. We use simplified methods for determining direction and speed of air stream in particular places in the boiler. Further we use simplified methods for the simulation of combustion processes and heat transfer as well. A particle system is used to simulate and visualise the behaviour of the coal particles and air streams in voxelized boiler space. We developed concept of virtual particles – they represent certain amount of coal, air, ash and other materials in a voxel under investigation.
An intelligent hybrid approach for design by features
(UNION Agency, 2002) Ding, Lian; Yue, Yong; Skala, Václav
This paper presents a new methodology for design-by-features. After a brief background study of design-by-features, a architecture with a feature library, feature-based model, feature library management and feature-based model management is introduced. A standard feature class is defined for feature library. Automatic feature-based model management covering interactive functions, identification of feature interaction and maintenance of the model validity is described. Finally, conclusions are drawn and further research summarised.

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