WSCG '2000: Conference proceeding

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http://hdl.handle.net/11025/15421

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Showing 1 - 20 out of 55 results

Persistent Naming for Parametric Models
(University of West Bohemia, 2000) Agbodan, Dago; Marcheix, David; Pierra, Guy; Skala, Václav
Nowadays, many commercial CAD systems support history-based, constraint-based and feature-based modelling. The use of these new capabilities raises the issue of persistent naming which refers to the problem of identifying entities in an initial parametric model and matching them in the re-evaluated model. The goal of this paper in to propose a naming mechanism and an hierarchical structure enabling to identify topological entities and to apprehend the "design intent".
Laziness, a Way to Improve Distributed Computation of the Ray Tracing Algorithm
(University of West Bohemia, 2000) Poitou, Olivier; Lecussan, Bernard; Bermes, Sébastien; Skala, Václav
This paper raises the issue of computational workload and memory load balancing to ray trace large scenes efficiently on a network of workstations. The task splitting is done on the image to be produced and not on the scene data to obtain a high performance level. To deal with the high memory requirements of such a distribution strategy, laziness is added to the base algorithm. This reduces the computing local memory requirements to the locally computed part of the image. It also reduces the sequential parts of the algorithm by making the voxelization process parallel. Many comparisons have been done using a manager/worker distribution algorithm on different scenes computed on a conventional network of workstations. Performance, load imbalance, communication overhead, and memory requirement results are given and discussed in this paper. Furthermore, this paper demonstrates that the proposed solution improves the results obtained with conventional algorithms, no matter what network used or however complex the image is.
Real-Time Virtual Cables Based on Kinematic Simulation
(University of West Bohemia, 2000) Hergenröther, Elke; Dähne, Patrick; Skala, Václav
We present an algorithm for the real-time simulation of virtual cables using inverse kinematics. A cable is modeled by consecutive cylinder segments of equal size. The segments are connected by ball joints. At every joint there is a spiral spring acting against the excursion of the joint. Given a start and an end position of the cable, the algorithm calculates the shape of the cable that leads to minimal total energy. The total energy is the sum of the potential energies of the segments and the elastic energies of the springs. First, the algorithm calculates a cable with minimal total energy consisting of two segments. This is taken as a starting basis for the computation of a cable consisting of four segments. At each following step, the number of segments is doubled and a new shape of the cable is calculated based on the solution of the previous step. The great advantage of this approach is the easy accommodation of the solution exactness to the available computation time. If the user of the VR application is moving the cable, he gets a fast but rough feedback. If he stops moving it, he/she gets an exact shape.
Computer Graphics, Business and Education: Making the Connection
(University of West Bohemia, 2000) Bannatyne, Mark; Ross, William A.; Skala, Václav
Professional educators cannot be isolated in their professions as simply conveyers of information who direct curriculum materials toward their students. The fact is that within our profession teaching very often occupies the smallest portion of our workday. In an effort to maintain a high standard of technological excellence in our programs we are responsible for continually reviewing and updating curricula. Indeed, our instructional materials must reflect the high standards that business and industry will demand of our students once they graduate and enter the world of work. An effort must also be made to recruit and encourage the perpetuation of our field by actively seeking out students at the public school level as a means of guiding future scholars toward a career in computer graphics. All these efforts require concentrated efforts and plans that have been well thought out so our programs may continue to grow and prosper. An idle approach to recruiting and securing continual support from business and industry will sound the death knell for any computer graphics program regardless of how well its curriculum may be laid out.
Information Contents of Fracture Lines
(University of West Bohemia, 2000) Leităo, H. C. G.; Stolfi, J.; Skala, Václav
Reassembling unknown broken objects from a large collection of fragments is a common problem in archaeology and other fields. Computer tools have recently been developed by the authors and by others, which try to help by locating pairs of fragments with matching outline shapes. These tools have been succesfully tested on small collections of fragments. Here we address the question of whether such tools can be expected to work for practical instances of the problem (103 to 105 fragments). To that end, we describe here a method to measure the average amount of information contained in the shape of a fracture line of given length. This parameter tells us how many false matches we can expect to find for that fracture among a given set of fragments; and we show that outline comparison should give useful results even for large instances.
Robust Incremental Polygon Triangulation for Fast Surface Rendering
(University of West Bohemia, 2000) Kumar, Subodh; Skala, Václav
This paper presents a simple, robust and practical, yet fast algorithm for triangulation of points on the domain of trimmed Bézier surfaces. These R 2 points are input to this algorithm by a surface sampler. A set of polygons is formed from these samples, which are then triangulated. We also show how to update the triangulation when the samples, and hence the polygons, are updated. The output is a set of triangle strips. The algorithm includes heuristics to avoid long and thin triangles. In addition, it also detects if the sampling of the trimming curve forms any non-simple polygons and corrects the triangulation by adding more samples. The triangulation algorithm is more generally applicable to polygons in a plane. We report an implementation of the algorithm and its performance on extensive surface-model walkthrough
New Theory of Pattern Recognition on the Basis of Stochastic Geometry
(University of West Bohemia, 2000) Fedotov, Nikolay; Shulga, Luydmila; Skala, Václav
The article offers a new approach towards the construction of recognition features independent of images’ displacement or linear deformation. The distinguishing characteristics of the group of features under study is representing each of them as a sequential composition of three functionals acting upon the function of one variable. The process to construct the new features suggested boasts of the advantages as follows: a)a host of new features can be easily constructed; b) the features obtained can be structurized along with parallel computations. Great many new features have been constructed to successfully solve the task of recognizing coloured images in biological systems, for instance, blood cells in gematology.
A Z-Buffer CSG Rendering Algorithm for Convex Objects
(University of West Bohemia, 2000) Nigel, Stewart; Geoff, Leach; Sabu, John; Skala, Václav
A new algorithm for image-space CSG rendering is presented, based on subtraction of convex objects in a specific sequence. The algorithm has been implemented on OpenGL PC graphics hardware, as well as SGI workstations. Advantages of the algorithm include simpler implementation, closer affinity to hardware capabilities and comparable performance to other image-space CSG algorithms. The new algorithm is described, and compared to previous algorithms, experimentally and theoretically. Some graphics hardware issues related to image-space CSG performance are also discussed.
Human Motion Synthesis Based on Iterated Function Systems
(University of West Bohemia, 2000) Lam, Stephen Wang-Cheung; Leung, Powis Lai-Yin; Skala, Václav
Region-Based Fractal Compression for Still Image
(University of West Bohemia, 2000) Chang, Yung-Ching; Shyu, Bin-Kai; Wang, Jia-Shung; Skala, Václav
Fractal image coding is a novel and attractive technique for still image compression. By utilizing the characteristic of self-similarity, an iterated function system can automatically converts an image into a set of affine transformation coefficients. However, the conventional block-based segmentation methods inadequately satisfy the natural image property and thus can’t achieve an efficient performance. In this paper, we propose a thorough fractal image compression system to approach the target of very low bit-rate. To more efficiently utilize the property of natural images, an image dependent region-based segmentation technique is proposed. This region-based process consists of two steps: First, we improve the performance of quadtree decomposition by utilizing the adaptive threshold method. Second, a merging scheme is introduced to the result of quadtree decomposition that combines several similar blocks into a small number of regions. We also provide a quadtree-based segmented chain code to efficiently record the contours of the regions. Moreover, a post-processing algorithm is applied according to region-based segmentation to eliminate the blocking artifact. The experimental results indicate that the proposed method has the potential to achieve comparable extreme low bit rate among the existing method at the same level of quality.
Incremental Conversion of 3D Wireframe Models to Polygonal Surface Models
(University of West Bohemia, 2000) Grosjean, Jérôme; Stein, Terii; Coquillart, Sabine; Skala, Václav
Though a large variety of methods has been developed to model 3D objects, most of them are based on the construction of solid objects or curved surfaces. This work is part of a sketch-based project for modeling arbitrarily polygonal shapes. The method for modeling 3D objects is based on the user drawing or removing of edges. This paper addresses the automatic computation of the 3D polygonal surface model from the 3D wire frame. A straightforward incremental algorithm is proposed allowing an update of the surface model for each modification of the 3D wire frame. Objects of any genus, or topological type are handled by the method.
An Immersive Virtual Environment for Special Relativity
(University of West Bohemia, 2000) Weiskopf, Daniel; Skala, Václav
In this paper, an immersive virtual environment is presented which allows the user to virtually explore and experience special relativity, including phenomena such as Lorentz contraction, time dilation, aberration, and finite speed of light. The relativistic-vehicle-control metaphor — a physically based camera control technique — is introduced for navigating at high velocities. Acceleration of the relativistic observer is investigated. Furthermore, tracking of both the position and velocity of the user is considered. A geometric approach to relativistic polygon rendering is described. The rendering pipeline is extended to accomplish the relativistic transformations in parallel. The implementation supports multiprocessor and multipipe systems for fast rendering and the same frame rates can be achieved for relativistic visualization as for non-relativistic rendering.
Visualization of Impulse Reponse of Virtual Accoustic Environments
(University of West Bohemia, 2000) Šporka, Adam J.; Slavík, Pavel; Skala, Václav
There are many methods that allow generate realistic 3D acoustic scenes. By means of new technologies it is possible to achieve a high level of realism. In many applications, the pictures are enhanced by sounds generated in 3D environment. This creates more realistic impression for the user. There are many methods that allow us to generate 3D sound and in such a way create high degree of reality in synthetic scenes. Nevertheless when generating sound in 3D environment, it is necessary to have relatively detailed information about the sound characteristics of the scene. Due to the complexity of this information it is necessary to visualize the sound distribution in the space where the sound will be generated. This paper describes a system of visualization of the impulse response of given acoustic environment whose development is one of our current research projects. We notice here its purpose, principles of implementation and basic applications.
Real-time Animation Technique for Flexible and Thin Objects
(University of West Bohemia, 2000) Kang, Young-Min; Choi, Jeong-Hyeon; Cho, Hwan-Gue; Lee, Do-Hoon; Park, Chan-Jong; Skala, Václav
In this paper, we propose an efficient technique for the animation of flexible thin objects. Mass-spring model was employed to represent the flexible objects. Many techniques have used the mass-spring model to generate plausible animation of soft objects. The easiest approach to animation with mass-spring model is explicit Euler method, but the explicit Euler method has serious disadvantage that it suffers from `instability problem'. The implicit integration method is a possible solution to overcome the instability problem. However, the most critical flaw of the implicit method is that it involves a large linear system. This paper presents a fast animation technique for mass-spring model with approximated implicit method. The proposed technique stably updates the state of n mass-points in O(n) time when the number of total springs are O(n). We also consider the interaction of the flexible object and air in order to generate plausible results.
Towards Calligraphic Interfaces: Sketching 3D Scenes with Gestures and Context Icons
(University of West Bohemia, 2000) Pereira, João P.; Jorge, Joaquim A.; Branco, Vasco; Ferreira, F. Nunes; Skala, Václav
GIDeS (Gesture-based Intuitive Design System) is a gesture-based modeling system that addresses the known ergonomic shortcomings of present-day CAD systems for conceptual shape design. GIDeS uses a tablet and stylus combination to combine the intuitive appeal of gesture-based interfaces with contextbased icons. GIDeS draws on previous modeling work, using contextual information and feedback to free users from remembering detailed modeling gestures, allowing them to concentrate on drawing, towards our end goal of bridging the chasm between paper and pencil and CAD interfaces in the early design stage.
An Improved Articulated Model of the Human Hand
(University of West Bohemia, 2000) McDonald, John; Toro, Jorge; Alkoby, Karen; Berthiaume, Andre; Pattaraporn, Chomwong; Christopher, Juliet; Davidson, Mary Jo; Furst, Jacob; Konie, Brian; Lancaster, Glenn; Lytinen, Steven; Roychoudhuri, Lopa; Sedgwick, Eric; Tomuro, Noriko; Wolfe, Rosalee; Skala, Václav
We present an improved anatomically based approach to modeling the human hand for use in the animation of American Sign Language. The joint rotations in the model are based on the bone and muscle configurations of the hand, and a forward kinematic solution is used to position the hand. In particular, we investigate the rotations of the base joint of the thumb. This joint is a saddle joint with non-trivial rotational axes and centers, and must be treated with care in such a model. We take advantage of several correlations between joint rotations in the hand to reduce the number of degrees of freedom in the model and provide a simple, intuitive and interactive interface for American Sign Language handshape transcription.
Human Movement Instruction System that Utilizes Avatar Overlays Using Stereoscopic Images
(University of West Bohemia, 2000) Ihara, Masayuki; Shimada, Yoshihiro; Kida, Kenichi; Shiwa, Shinichi; Ishibashi, Satoshi; Mizumori, Takeshi; Skala, Václav
In the Mixed Reality environment that combines the real world and the virtual world it is important to control the ’place’ that comprises both real and virtual objects. In this paper, we study the overlay of humans and avatars in virtual space in the creation of an immersive human movement instruction system that works through a network. In this system, users wear stereoscopic glasses and motion capture devices and perform within an immersive virtual space experience system called CAVE TM. A user can look at a stereoscopic image of an avatar that is displayed over his or her own body. In this project, the authors connected two CAVE TM systems to a network to develop a system that enables model movement instruction and judgment of movement skills to be implemented by people in remote locations. This paper will introduce the setup and configuration of this system.
The Gait Sensing Disc - A Compact Locomotion Device for the Virtual Environment
(University of West Bohemia, 2000) Huang, Jiung-yao; Chiu, Wen-hsin; Lin, Yung-ting; Tsai, Ming-tien; Bai, Hua-hseng; Tai, Chi-fu; Gau, Chung-yun; Lee, Hwa-teng; Skala, Václav
The locomotion device is an input interface, which can sense the walking pace and direction of the user, for the virtual reality system. This paper presents a new type of locomotion device called Omni-direction Ball-bearing Disc Platform(OBDP), which allows the user to walk naturally inside the virtual environment. Instead of using the 3D tracker, arrays of ball-bearing sensors on a disc are used to detect the pace and an orbiting frame to identify the walking direction. No other sensor, except the head tracker to detect the user ’s head rotation, is required on the user’s body. In addition, the ball-bearing on the sensor slips the user’s foot back to the center position of the disc. A prototype of the overhead crane training simulator that fully explores the advantage of the OBDP is also designed and introduced in this paper.
XML Based Mobile Services
(University of West Bohemia, 2000) Marttila, Outi; Vuorimaa, Petri; Skala, Václav
The most remarkable trends in communication have been the huge popularity of Internet and the growth of digital cellular telephony usage. There is a strong demand to combine these two in the form of mobile Internet access. This paper discusses the service implementation issues for the wireless environment. The requirements placed on the services and service development by the mobility are presented, and the usage of the next generation, XML based modeling languages in the wireless services is analyzed. The results are based on the experiments gained from the implementation of three demonstration services.
Interactive Focus and Context Display of Large Raster Images
(University of West Bohemia, 2000) Rauschenbach, Uwe; Weinkauf, Tino; Schumann, Heidrun; Skala, Václav
This paper presents the Rectangular FishEye View, an interactive focus-and-context presentation technique for large raster images on mobile computers with small displays and limited processing power. Both the viewing of locally available images and the demand-driven display and transmission of remotely-stored images are supported by the technique. The underlying geometry calculations are explained, and the design decisions for supporting rapid interactive feedback are discussed. A scenario is described which demonstrates the performance of the method.

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