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Light Space Cascaded Shadow Maps Algorithm for Real Time Rendering

Journal of Computer Science & technology 2011年第1期26卷 176-186页

作者：梁晓辉马上岑丽霞于卓 State Key Lab.of Virtual Reality Technology and Systems School of Computer Science and EngineeringBeihang University

Owing to its generality and efficiency, Cascaded Shadow Maps （CSMs） has an important role in real-time shadow rendering in large scale and complex virtual environments. However, CSMs suffers from redundant rendering problem -- objects are rendered undesirably to different shadow map textures when view direction and light direction are not perpendicular. In this paper, we present a light space cascaded shadow maps algorithm. The algorithm splits a scene into non-intersecting layers in light space, and generates one shadow map for each layer through irregular frustum clipping and scene organization, ensuring that any shadow sample point never appears in multiple shadow maps. A succinct shadow determination method is given to choose the optimal shadow map when rendering scenes. We also combine the algorithm with stable cascaded shadow maps and soft shadow algorithm to avoid shadow flicking and produce soft shadows. The results show that the algorithm effectively improves the efficiency and shadow quality of CSMs by avoiding redundant rendering, and can produce high-quality shadow rendering in large scale dynamic environments with real-time performance.

关键词： shadow mapping light space redundant rendering large scale dynamic environments

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NURBS curve blending using extension

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2009年第4期10卷 570-576页

作者： Yong-jin LIU Rong-qi QIU Xiao-hui LIANG Tsinghua National Lab for Information Science and Technology Tsinghua University Beijing 100084 China State Key Lab of Virtual Reality Technology and Systems Beihang University Beijing 100191 China

Curve and surface blending is an important operation in CAD systems, in which a non-uniform rational B-spline （NURBS） has been used as the de facto standard. In local comer blending, two curves intersecting at that comer are first made disjoint, and then the third blending curve is added-in to smoothly join the two curves with G^1- or G^2-continuity. In this paper we present a study to solve the joint problem based on curve extension. The following nice properties of this extension algorithm are exploited in depth：（1） The parameterization of the original shapes does not change; （2） No additional fragments are created. Various examples are presented to demonstrate that our solution is simple and efficient.

关键词： Curve blending Curve fairing Curve extension Non-uniform rational B-spline (NURBS)

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A physical based meshless method for soft tissue deforming

A physical based meshless method for soft tissue deforming

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2011 IEEE International Symposium on IT in Medicine and Education, ITME 2011

作者： Hao, Aiming Huang, Zhen State Key Lab of Virtual Reality Technology and Systems Beijing China

ISBN: (纸本)9781612847023

This paper concentrated on how to apply meshless method to do physical based soft tissue deformation. First we approximated the deformation field using a Moving Least Squares (MLS) approximation method. Then, a compact force computation was applied to accelerate the physical computation speed. Finally we implemented a surface animation method to simulate the deformation of soft tissue under external forces. We made experiments with real properties of human soft tissue and the results showed that our method successfully made physical based deformation of human soft tissue. © 2011 IEEE.

关键词： Deformation

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Dynamic Characteristics Analysis and Vibration Experiment of Upper-time of Flight Counter (U-ToFC)

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Chinese Journal of Mechanical Engineering 2012年第5期25卷 868-874页

作者： WU Qiong ZHANG Yidu SONG Sunguang State Key Lab of Virtual Reality Technology and Systems Beihang UniversityBeijing 100191China School of Mechanical Engineering andAutomation Beihang UniversityBeijing 100191China

The dynamic characteristic parameters of Up-time of Flight Counter （U-ToFC） are important for research of structure optimization and reliability. However, the current simulation is performed based on homogenous material and simplified constraint model, the correct and reliability of results are difficult to be guaranteed. The finite element method based on identification of material parameters is proposed for this investigation on dynamic analysis, simulation and vibration experiment of the U-ToFC. The structure of the U-ToFC is complicated. Its＇ outside is made of aluminum alloy and inside contains electronic components such as capacitors, resistors, inductors, and integrated circuits. The accurate material parameters of model are identified difficultly. Hence, the parameters identification tests are performed to obtain the material parameters of this structure. On the basis of the above parameters, the experiment and FEA are conducted to the U-ToFC. In terms of the flight acceptance test level, and two kinds of joints condition between the U-ToFC and fixture are considered. The natural frequencies, vibration shapes and the response of the power spectral density of the U-ToFC are obtained. The results show simulation which is based on parameters identification is similar with vibration experiment in natural frequencies and responses. The errors are less than 10%. The vibration modes of simulation and experiment are consistent. The paper provides a more reliable computing method for the dynamic characteristic analysis of large complicated structure.

关键词： random vibration dynamical characteristic parameters finite element analysis identification of material parameters

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Haptic based teleoperation with master-slave motion mapping and haptic rendering for space exploration

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Chinese Journal of Aeronautics 2019年第3期32卷 723-736页

作者： Guanyang LIU Xuda GENG Lingzhi LIU Yan WANG State Key Lab of Virtual Reality Technology and Systems Beihang University School of Mechanical Engineering and Automation Beihang University Key Laboratory of Space Utilization Technology and Engineering Center for Space Utilization Chinese Academy of Sciences

This paper presents a new solution to haptic based teleoperation to control a large-sized slave robot for space exploration, which includes two specially designed haptic joysticks, a hybrid master-slave motion mapping method, and a haptic feedback model rendering the operating resistance and the interactive feedback on the slave side. Two devices using the 3 R and DELTA mechanisms respectively are developed to be manipulated to control the position and orientation of a large-sized slave robot by using both of a user's two hands respectively. The hybrid motion mapping method combines rate control and variable scaled position mapping to realize accurate and efficient master-slave control. Haptic feedback for these two mapping modes is designed with emphasis on ergonomics to improve the immersion of haptic based teleoperation. A stiffness estimation method is used to calculate the contact stiffness on the slave side and play the contact force rendered by using a traditional spring-damping model to a user on the master side stably. Experiments by using virtual environments to simulate the slave side are conducted to validate the effectiveness and efficiency of the proposed solution.

关键词： Teleoperation Haptic device Remote control Haptic rendering Space exploration

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A component-based aircraft instrument rapid modeling tool

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Journal of Zhejiang University-Science C(Computers and Electronics) 2010年第11期11卷 911-918页

作者： Fang-wen LI Xu-kun SHEN State Key Lab of Virtual Reality Technology and Systems School of Computer Science Beihang University Beijing 100191 China

Component-based software reuse and development is considered to be the best way to improve the efficiency and quality of *** meet the demands of aircraft instrument exhibition in an aviation virtual library,we present a modeling and simulation tool for cockpit instruments on component methods,achieving display functionality and providing a visual interaction platform in the aviation virtual *** the rapid model construction and reuse of virtual library resources,we classify entities in the cockpit into several categories by their behavior,and design a template for each category to describe its *** efficiently reduces the modeling cycle,and thus largely helps users to take advantage of the library resource.

关键词： Components Rapid modeling Simulation

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A point models simplification based on energy and screen resolution for mobile devices

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Journal of Information and Computational Science 2009年第5期6卷 1945-1952页

作者： He, Zhiying Liang, Xiaohui Duan, Wei State Key Lab. of Virtual Reality Technology and Systems School of Computer Science and Engineering Beihang University Beijing 100191 China

Mobile devices have two characteristics that clearly different from the conventional PC systems: low resolution and limited energy. Traditional simplification algorithm computes the error in the object space, which is pure geometry simplification. They do not consider the screen resolution of display terminal. In this paper, we present a novel point models simplification based on energy and screen resolution for mobile devices. The approach calculates the error based on the ultimate display effect, which means it could from the visual effect to determine which part should be simplified first. In addition, we consider the trade-off between visual quality and energy consumption. Energy is used to control the simplification level. Finally, we apply the method to a point models simplification which is based on MLS and splat, and then render the result points on mobile devices. © 2009 Binary Information Press.

关键词： Energy utilization

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Quick reconstruction of cameras and quasi-dense geometry from unordered photos

Quick reconstruction of cameras and quasi-dense geometry fro...

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2009 WRI World Congress on Computer Science and Information Engineering, CSIE 2009

作者： Shuang, He Yue, Qi Fei, Hou State Key Lab of Virtual Reality Technology and Systems Beihang University China

ISBN: (纸本)9780769535074

This paper presents a novel approach to quick reconstruction of cameras and quasi-dense geometry from unordered photos of a scene. With three reconstruction goals: reliable camera postures, high-density scene geometry, and a low cost of time, our approach consists of two stages: pairwise relating and two-tier reconstruction. At the first stage, to obtain better putative matches, we impose bidirectional feature matching and disparity constraint;to achieve better normalization, we perform approximate self-calibration using EXIF tag. The second stage includes a sparse and a quasi-dense reconstruction with different pivot respectively, adding selection strategies to avoid degenerate cases and improve time efficiency. © 2008 IEEE.

关键词： Cameras

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Multi-Scale Feature Fusion Network for VideoBased Person Re-Identification

Multi-Scale Feature Fusion Network for VideoBased Person Re-...

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2021 IEEE International Conference on Electronic technology, Communication and Information, ICETCI 2021

作者： Liu, Penggao Ai, Mingjing Shan, Guozhi State Key Lab of Virtual Reality Technology and Systems Beihang University Beijing China

ISBN: (纸本)9781665432511

In recent years, person re-identification technology has been greatly developed. Image-based person reidentification algorithms have achieved excellent performance on open source datasets. In contrast, the development of videobased person re-identification technology is relatively backward. At present, the main research work of video-based person re-identification algorithms is focused on the processing of temporal information in the picture sequence. Complex appearance features are not effective when performing temporal fusion, so the frame-level features used are almost based on global features. This paper proposes a video person re-identification model based on multi-scale feature fusion. The multi-scale feature fusion of the model is embodied in the design of the frame-level feature extraction module. This module extracts the frame-level features of different scales, and then catenates them together into vectors, which not only improves the feature discrimination degree, but also makes the catenated frame-level features carry out effective temporal fusion, and the test results on the Mars dataset have reached a competitive level. At the same time, a series of comparative experiments were carried out on the model parameters to achieve further optimization of performance. ©2021 IEEE.

关键词： Statistical tests

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Soft tissue simulation with bimanual force feedback

Soft tissue simulation with bimanual force feedback

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International Conference on Audio, Language and Image Processing

作者： Zhao, Hui Wang, Dang-Xiao State Key Lab. of Virtual Reality Technology and Systems Beihang University China

ISBN: (纸本)9781424458653

Soft tissue simulation with bimanual force feedback is one of the main research topics toward practical application of surgery simulation. A method for the simulation of soft object using Mass-Spring model is presented to deform human tissue in the bimanual haptic feedback environment. A multi-thread simulation framework is employed to support real-time force feedback calculation and the deformation of the soft object. Haptic force is calculated based on a hybrid physical/geometric model and is filtered before sent to the haptic device in order to get stable force feedback. Two experiments are carried out to evaluate real-time performance and stability. Finally, a preliminary example of application in human tissue simulation is introduced. ©2010 IEEE.

关键词： Tissue

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