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6th ACM Symposium on Solid Modeling and Applications

作者： Steiner, D. Fischer, A. CMSR Lab. for Comp. Graphics and CAD Department of Mechanical Engineering Technion-Israel Inst. of Technology Haifa 32000 Israel

A new method, based on a height function, to extract the shape of the topological graph of a freeform object was proposed. The proposed method was applied directly on a dense triangulated mesh for calculation of the 3D isocurves and extraction of the topological graph. The comp.tation involved application of the marching cube algorithm, initial value conditions, partial differential equations and Lapalacian equations.

关键词： Surface topography

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Modeling and Visualizing the Cultural Heritage Data Set of Graz

Modeling and Visualizing the Cultural Heritage Data Set of G...

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Proceedings VAST 2001 Virtual Reality, Archeology, and Cultural Heritage

作者： Zach, Christopher Klaus, Andreas Bauer, Joachim Karner, Konrad Grabner, Markus VRVis Res. Ctr. Virtual Reality/V. Inst. for Comp. Graphics and Vision Inffeldgasse 16 Graz Austria

ISBN: (纸本)1581134479

The inner city (Old Town) of Graz will be the European cultural capital in 2003. In this paper we present preliminary results on the reconstruction and visualization of this kind of cultural heritage data. Starting with a simple block model obtained by converting 2 1/2 dimensional GIS (geographic information system) data we focus on the image based modeling of the facades. Herein we illustrate a robust search for corresponding points to estimate the relative orientation between image pairs. Additional, we outline our real-time rendering approach based on a LOD-R-tree concept. Special attention is paid on the LOD (level of detail) generation for historic buildings where two different ways working in 2D and 3D are explained. The visualization system is communicating asynchronously with a database system storing the LOD-R-tree data structure. This client-server configuration provides interactive navigation through the virtual scene and the scalability of a database management system.

关键词： Virtual reality

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A general method for comp.ting the reachable space of mechanisms

A general method for computing the reachable space of mechan...

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2001 ASME Design Engineering Technical Conference and comp.ters and Information in Engineering Conference

作者： Fuhrmann, Artur Schömer, Elmar DaimlerChrysler Res. and Technology Virtual Reality Competence Center Ulm Germany Max-Planck-Inst. for Comp. Science Algorithms and Complexity Group Saarbrücken Germany

A new methodology is presented for comp.ting a minimal envelope for the reachable space of a mechanism, i.e. the space that contains a given mechanism in all its admissible configurations. The research is motivated by the packaging process in Digital Mock-Up applied in automotive industry. An important task in the concept phase, the automated determination of the space requirement for all parts, is still an unsolved problem in the case of mechanisms. The particular benefit of the method presented is its generality and robustness: It is able to deal with both open- and closed-loop mechanisms. The reachable space is comp.ted with regard to the geometric description of each part. The approximation is enclosing and always converges in a uniform way and the tolerance can be pre-defined by the user. The method combines the use of bounding object hierarchies and the application of interval analysis. It is also able to approximate the swept volume of an object following a parameterized trajectory. We describe how the efficiency can be improved by lazy evaluation and by a deeper problem analysis. The presented algorithms are implemented and tested to a large extent.

关键词： Manipulators

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DRR volume rendering using splatting in shear-warp context

DRR volume rendering using splatting in shear-warp context

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2000 IEEE Nuclear Science Symposium Conference Record

作者： Cai, Wenli Sakas, Georgios Fraunhofer Inst. for Comp. Graphics Rundeturmstrasse 6 D-64283 Darmstadt Germany

Digital Reconstruction Radiography (DRR) is an important technique in radiotherapy imaging applications. DRR volume rendering aims at rendering DRR images using CT or other tomographic data sets. In addition to the appropriate optical model, the interactive and realistic DRR imaging depends mainly on an accurate attenuation coefficient transfer function, which is usually a piecewise function, and an interactive rendering algorithm with reasonable rendering quality. In this paper, we first present a realistic DRR transfer function based on the mass attenuation coefficient comp.sition. Then, we introduce an object space DRR rendering algorithm, DRR splatting in the sheared object space. The DRR image qualities under different rendering algorithms are comp.red, including ray casting, Fourier volume rendering, projective shear-warp and splatting shear-warp. Finally, a line encoding technique is adopting to accelerate DRR rendering.

关键词： Radiography

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Mediazine - A combination of television, radio, www, telecommunication and 3D comp.ter sound and graphics 00

Mediazine - A combination of television, radio, www, telecom...

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Proceedings of the Third International Conference on Collaborative Virtual Environments (CVE 2000)

作者： Schiffner, Norbert Chodura, Hartmut Fraunhofer Inst. for Comp. Graphics Rundeturmstraße 6 D-64283 Darmstadt Germany

ISBN: (纸本)1581133030

The Mediazine is a distributed interactive multimedia magazine for the Internet including text, applications, images, live audio, live-video, animations, 3D comp.ter graphics. Users and Actors can interactively meet each other in a shared virtual environment that is distributed via comp.ter network. The system uses high quality multimedia streams. For the playback of audio an own developed Spatial Audio Server is used. On one hand it provides output for the communication system, an Internet-Telephone. On the other hand it manages sound of applications like TV and radio. Additionally spatialized binaural output is provided for the sound: In the virtual environment participants speech the can be located from where their avatars are placed. The participant'S sound is coming from the place where the video is presented. The paper describes how the system is built. It focuses on the mechanism of controlling the amount and quality of multimedia information on behalf of the network and the receiver system. Furthermore, the paper discusses how agents can be integrated as comp.nents in the system that is organized as an object-oriented application framework. Authors can take advantage of this concept specifying the agent'S behavior efficiently in a target domain specific way. Finally, a prototype implementation of the mediazine system is presented.

关键词： Virtual reality

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Multi-layered architecture for sketch-based interaction within virtual environments

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comp.ters and graphics (Pergamon) 2000年第6期24卷 851-867页

作者： Bimber, Oliver Encarnação, L. Miguel Stork, André Fraunhofer Inst. for Comp. Graphics Joachim-Jungius-Strasse 11 18059 Rostock Germany Fraunhofer Ctr. Res. Comp. G. 321 S. Main St. Providence RI 02903 United States Fraunhofer Inst. for Comp. Graphics Rundeturmstrasse 6 64283 Darmstadt Germany

In this article, we describe a multi-layered architecture for sketch-based interaction within virtual environments. Our architecture consists of eight hierarchically arranged layers that are described by giving examples of how they are implemented and how they interact. Focusing on table-like projection systems (such as Virtual Tables or Responsive Workbenches) as human-centered output-devices, we show examples of how to integrate parts or all of the architecture into existing domain-specific applications - rather than realizing new general sketch applications - to make sketching an integral part of the next-generation human-comp.ter interface.

关键词： Virtual reality

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Fast data association algorithm of passive sensor tracking

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Tien Tzu Hsueh Pao/Acta Electronica Sinica 2000年第12期28卷 45-47+44页

作者： Wang, Ming-Hui You, Zhi-Sheng Zhao, Rong-Chun Zhang, Jian-Zhou Feng, Zi-Liang 1105 of the Dept. of Comp. Sci. Northwestern Polytech. Univ. Xi'an 710071 China Inst. of Image and Graphics Sichuan Univ. Chengdu 610064 China

A fast data association algorithm based on the attribute intensity of space intersection for the static association problem is presented in this paper. All of sensors are passive sensors, which obtained the angle only, in presence of clutter, missed detection, false alarm, and an unknown number and location of targets. comp.rison of our method to the classical algorithm demonstrates that our algorithm is superior to the classical approach in terms of comp.tational comp.exity and association accuracy via several simulations.

关键词： Sensors

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K-D trees are better when cut on the longest side

K-D trees are better when cut on the longest side

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8th Annual European Symposium on algorithms, ESA 2000

作者： Dickerson, Matthew Duncan, Christian A. Goodrich, Michael T. Dept of Math and Comp Sci Middlebury College MiddleburyVT05753 United States Algorithms and Complexity Group Max-Planck-Inst. Für Informatik SaarbrückenD-66123 Germany Dept of Comp. Sci Johns Hopkins Univ BaltimoreMD21218 United States

ISBN: (纸本)354041004X

We show that a popular variant of the well known k-d tree data structure satisfies an important packing lemma. This variant is a binary spatial partitioning tree T defined on a set of n points in IRd, for fixed d ≥ 1, using the simple rule of splitting each node’s hyperrectangular region with a hyperplane that cuts the longest side. An interesting consequence of the packing lemma is that standard algorithms for performing approximate nearest-neighbor searching or range searching queries visit at most O(logd–1n) nodes of such a tree T in the worst case. Traditionally, many variants of k-d trees have been empirically shown to exhibit polylogarithmic performance, and under certain restrictions in the data distribution some theoretical expected case results have been proven. This result, however, is the first one proving a worst-case polylogarithmic time bound for approximate geometric queries using the simple k-d tree data structure. © Springer-Verlag Berlin Heidelberg 2000.

关键词： Nearest neighbor search

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K-D trees are better when cut on the longest side

Lecture Notes in Computer Science (including subseries Lectu...

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Lecture Notes in comp.ter Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) 2000年 1879卷 179-190页

作者： Dickerson, Matthew Duncan, Christian A. Goodrich, Michael T. Dept. Of Math and Comp. Sci Middlebury College MiddleburyVT05753 United States Algorithms and Complexity Group Max-Planck-Inst. Für Informatik SaarbrückenD-66123 Germany Dept. Of Comp. Sci Johns Hopkins Univ BaltimoreMD21218 United States

We show that a popular variant of the well known k-d tree data structure satisfies an important packing lemma. This variant is a binary spatial partitioning tree T defined on a set of n points in Rd, for fixed d ≥ 1, using the simple rule of splitting each node’s hyperrectangular region with a hyperplane that cuts the longest side. An interesting consequence of the packing lemma is that standard algorithms for performing approximate nearest-neighbor searching or range searching queries visit at most O(logd-1 n) nodes of such a tree T in the worst case. Traditionally, many variants of k-d trees have been empirically shown to exhibit polylogarithmic performance, and under certain restrictions in the data distribution some theoretical expected case results have been proven. This result, however, is the first one proving a worst-case polylogarithmic time bound for approximate geometric queries using the simple k-d tree data structure. © Springer-Verlag Berlin Heidelberg 2000.

关键词： Nearest neighbor search

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A Discrete Algorithm for Crystal Structure Prediction of Organic Molecules

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Acta Crystallographica Section A: Foundations of Crystallography 1997年第2期53卷 225-235页

作者： Hofmann, Detlef W. M. Lengauer, Thomas Inst. for Algorithms/Sci. Comp. Ger. Natl. Res. Ctr. Info. Technol. Schloss Birlinghoven 53754 Sankt Augustin Germany Department of Computer Science University of Bonn 53117 Bonn Römerstrasse 164 Germany

A new algorithm, FlexCryst, is presented for fast crystal structure prediction. The algorithm differs from existing algorithms in that it performs the analysis on the basis of only a single molecule and uses potentials for scoring energy that are derived statistically from a set of data on molecular structures. In a first step, the algorithm creates various potential unit cells. In the second step, a set of candidates for translation vectors for corresponding crystals is generated. In the third step, the algorithm selects triples of candidate vectors to form potential crystal structures. The fourth step ranks the crystal structures with respect to their energy as estimated by a suitable scoring function. In the last step, the crystal structures are clustered according to a newly defined measure of similarity for crystal structures. At the moment, the program can handle only triclinic crystals with one molecule per asymmetric unit. The algorithm was tested on a set of 131 experimentally resolved crystals of space group P1 and 95 crystals of space group P1̄ from the Cambridge Structural Database. For P1, in 129 cases (98%), the observed crystal structure is among the crystal structures generated by the algorithm. The run time of the algorithm is a few seconds per molecule on a standard workstation. For P1̄, the experimental structure has been found among the proposed structures in 81 cases (85%). Owing to the more comp.ex unit cell for this space group, the run time increases to about 2 h per molecule.

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