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Now showing 1 - 10 of 134
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    Network Services
    (Blackwell Publishers Ltd and the Eurographics Association, 1997)
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    Introduction to VRML 97
    (Eurographics Association, 1997) Nadeau, David
    VRML (the Virtual Reality Modeling Language) has emerged as the de facto standard for describing 3-D shapes and scenery on the World Wide Web. VRML’s technology has very broad applicability, including web-based entertainment, distributed visualization, 3-D user interfaces to remote web resources, 3-D collaborative environments, interactive simulations for education, virtual museums, virtual retail spaces, and more. VRML is a key technology shaping the future of the web. Participants in this tutorial will learn how to use VRML 97 (a.k.a. ISO VRML, VRML 2.0, and Moving Worlds) to author their own 3-D virtual worlds on the World Wide Web. Participants will learn VRML concepts and terminology, and be introduced to VRML’s text format syntax. Participants also will learn tips and techniques for increasing performance and realism. The tutorial includes numerous VRML examples and information on where to find out more about VRML features and use.
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    A Flexible Architecture for Virtual Humans in Networked Collaborative Virtual Environments
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Sunday Pandzic, Igor; Lee, Elwin; Magnenat Thalmann, Nadia; Capin, Tolga K.; Thalmann, Daniel
    Complex virtual human representation provides more natural interaction and communication among participants in networked virtual environments, hence it is expected to increase the sense of being together within the same virtual world. We present a flexible framework for the integration of virtual humans in networked collaborative virtual environments. A modular architecture allows flexible representation and control of the virtual humans, whether they are controlled by a physical user using all sorts of tracking and other devices, or by an intelligent control program turning them into autonomous actors. The modularity of the system allows for fairly easy extensions and integration with new techniques making it interesting also as a testbed for various domains from "classic" VR to psychological experiments. We present results in terms of functionalities, example applications and measurements of performance and network traffic with an increasing number of participants in the simulation.
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    On the Computational Requirements of Virtual Reality Systems
    (Eurographics Association, 1997) Dévai, Frank
    The computational requirements of high-quality, real-time rendering exceeds the limits of generally available computing power. However illumination effects, except shadows, are less noticeable on moving pictures. Shadows can be produced with the same techniques used for visibility computations, therefore the basic requirements of real-time rendering are transformations, pre-selection of the part of the scene to be displayed and visibility computations. Transformations scale well, ie, their time requirement grows linearly with the input size. Pre-selection, if implemented by the traditional way of polygon clipping, has a growing rate of N logN in the worst case, where N is the total number of edges in the scene. Visibility computations, exhibiting a quadratic growing rate, are the bottleneck from a theoretical point of view. Three approaches are discussed to speed up visibility computations: (i) reducing the expected running time to O(NlogN) (ii) using approximation algorithms with O(NK) worst-case time, where K is the linear resolution of the image, and (iii) applying parallel techniques leading to logarithmic time in the worst-case. Though the growing rate of the time requirement of pre-selection is significantly slower than that of visibility, it is demonstrated that pre-selection has to deal with a significantly higher amount of data than visibility computations, as the average clipping volume is 1/27 of the volume of the model.
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    VIZARD - Visualization Accelerator for Realtime Display
    (The Eurographics Association, 1997) Knittel, Günter; Straßer, Wolfgang; A. Kaufmann and W. Strasser and S. Molnar and B.-O. Schneider
    Volume rendering has traditionally been an application for supercomputers, workstation networks or expensive special-purpose hardware. In contrast, this report shows how far we have reached using the other extreme: the low-end PC platform. We have alleviated the mismatch between this demanding application and the limited computational resources of a PC in three ways: several stages in the visualization pipeline are placed into a preprocessing step, the volume rendering algorithm was optimized using a special data compression scheme, and the algorithm has been implemented in hardware as a PCI-compatible coprocessor (lXZ,4RD). These methods give us a frame rate of up to 1OHz for 256 <sup>3</sup> data sets and an acceptable image quality, although the accelerator prototype was built using relatively slow FPGA-technology. In a low-cost environment a coprocessor must not be more expensive than the host itself, and so VIZARD was designed to be manufacturable for a few hundred dollars. The special data compression scheme allows the data set to be placed into the main memory of the PC and eliminates the need for an expensive, separate volume memory. The entire visualization system consists of a portable PC with two built-in accelerator boards. Despite its small size, the system provides perspective raycasting for realtime walk-throughs. Additional features include stereoscopic viewing using shutter glasses and volume animation.
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    A Million Polygons, a Million Pixels: Which is Heavier?
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Sillion, Francois X.
    The impressive progress of rendering software and hardware over the last two decades often leads to the - too rapid - conclusion that high-quality 3D imagery can now be incorporated in all sorts of applications. Interestingly, these advances allow more and more complex applications to be envisioned: however, an increase in processing power is not necessarily used to treat the same problem faster, but also creates a desire to attack larger problems. In many ways the models for visual simulation or engineering applications grow faster than the graphics systems! recent work on image-based rendering and modeling shows a growing awareness that traditional 3D methods may not scale well for the current and coming complexity levels.This talk will examine some of the challenges lying ahead for the development of future graphics applications. Specifically, when is it better to use pixels than polygons? when is a 3D model required? how can we mix and match competing approaches? can image-based approaches help for different applications such as lighting simulations? some issues related to network applications will also be discussed.
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    Tunnel-Free Supercover 3D Polygons and Polyhedra
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Andres, Eric; Nehlig, Philippe; Francon, Jean
    A new discrete 3D line and 3D polygon, called Supercover 3D line and Supercover 3D polygon, are introduced. Analytical definitions are provided. The Supercover 3D polygon is a tunnel free plane segment defined by vertices and edges. An edge is a Supercover 3D line segment. Two different polygons can share a common edge and if they do, the union of both polygons is tunnel free. This definition of discrete polygons has the "most" properties in common with the continuous polygons. It is particularly interesting for modeling of discrete scenes, especially using tunnel-free discrete polyhedra. Algorithms for computing Supercover 3D Lines and Polygons are given and illustrated.
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    Synthesizing Novel Views from Unregistered 2-D Images
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Havaldar, Parag; Lee, Mi-Suen; Medioni, Gerard
    Synthesizing the image of a 3-D scene as it would be captured by a camera from an arbitrary viewpoint is a central problem in Computer Graphics. Given a complete 3-D model, it is possible to render the scene from any viewpoint. The construction of models is a tedious task. Here, we propose to bypass the model construction phase altogether, and to generate images of a 3-D scene from any novel viewpoint from prestored images. Unlike methods presented so far, we propose to completely avoid inferring and reasoning in 3-D by using projective invariants. These invariants are derived from corresponding points in the prestored images. The correspondences between features are established off-line in a semi-automated way. It is then possible to generate wireframe animation in real time on a standard computing platform. Well understood texture mapping methods can be applied to the wireframes to realistically render new images from the prestored ones. The method proposed here should allow the integration of computer generated and real imagery for applications such as walkthroughs in realistic virtual environments. We illustrate our approach on synthetic and real indoor and outdoor images.
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    A Multiscale Approach to Integrated Volume Segmentation and Rendering
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Westermann, Rudiger; Ertl, Thomas
    A number of techniques have been proposed for rendering volumetric scalar data sets. Techniques have also been proposed for analyzing the three dimensional information contents of the underlying domain, but traditionally the data analysis part is left as a post-processing step which only involves the rendered two dimensional images. In this paper, we describe a visualization method for scalar volume data which integrates explicit knowledge of the underlying domain into the rendering process. The key of this approach lies in a hierarchical description of the discrete signal, which is decomposed into a sequence of multiscale representations. We describe a technique for the analysis of structures within the data. This allows for the segmentation and classification of the relevant features and can be used to improve their visual sensation. We also address the problem of accelerating the final rendering pass by integrating the extracted object space information into the ray traversal process.
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    An Algorithmic Reflectance and Transmittance Model for Plant Tissue
    (Blackwell Publishers Ltd and the Eurographics Association, 1997) Baranoski, Gladimir V.G.; Rokne, Jon G.
    Recent developments in rendering have provided very realistic images. However, these images rarely show organic objects. We believe that one of the main difficulties of rendering these objects realistically is the lack of reflectance and transmittance models oriented to organic materials. In this paper an algorithmic reflectance and transmittance model for plant tissue oriented to computer graphics applications is presented. The model accounts for the three components of light propagation in plant tissues, namely surface reflectance, subsurface reflectance and transmittance, and mechanisms of light absorption by pigments present in these tissues. The model design is based on the available biological information, and it is controlled by a small number of biologically meaningful parameters. Its formulation, based on standard Monte Carlo techniques, guarantees its easy incorporation into most rendering systems. The spectral curves of reflectance and transmittance computed by the model are compared with measured curves from actual experiments.