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LANDING AN UNMANNED AIR VEHICLE: VISION BASED MOTION ESTIMATION AND NONLINEAR CONTROL

Asian Journal of Control 2008年第3期1卷

作者： Omid Shakernia Yi Ma T. John Koo Shankar Sastry Dept. of Electrical Engineering & Computer Science University of California at Berkeley Berkeley CA94720-1774 U.S.A. Tak-Kuen John Koo received the B.Eng. degree in 1992 in Electronic Engineering and the M.Phil. in 1994 in Information Engineering both from the Chinese University of Hong Kong. From 1994 to 1995 he was a graduate student in Signal and Image Processing Institute at the University of Southern California. He is currently a Ph.D. Candidate in Electrical Engineering and Computer Sciences at the University of California at Berkeley. His research interests include nonlinear control theory hybrid systems inertial navigation systems with applications to unmanned aerial vehicles. He received the Distinguished M.Phil. Thesis Award of the Faculty of Engineering The Chinese University of Hong Kong in 1994. He was a consultant of SRI International in 1998. Currently he is the team leader of the Berkeley AeRobot Team and a delegate of The Graduate Assembly University of California at Berkeley. He is a student member of IEEE and SIAM. S. Shankar Sastry received his Ph.D. degree in 1981 from the University of California Berkeley. He was on the faculty of MIT from 1980-82 and Harvard University as a Gordon McKay professor in 1994. He is currently a Professor of Electrical Engineering and Computer Sciences and Bioengineering and Director of the Electronics Research Laboratory at Berkeley. He has held visiting appointments at the Australian National University Canberra the University of Rome Scuola Normale and University of Pisa the CNRS laboratory LAAS in Toulouse (poste rouge) and as a Vinton Hayes Visiting fellow at the Center for Intelligent Control Systems at MIT. His areas of research are nonlinear and adaptive control robotic telesurgery control of hybrid systems and biological motor control. He is a coauthor (with M. Bodson) of “Adaptive Control: Stability Convergence and Robustness Prentice Hall 1989.” and (with R. Murray and Z. Li) of “A Mathematical Introduction to Robotic Manipulati

In this paper, we use computer vision as a feedback sensor in a control loop for landing an unmanned air vehicle (UAV) on a landing pad. The vision problem we address here is then a special case of the classic ego-motion estimation problem since all feature points lie on a planar surface (the landing pad). We study together the discrete and differential versions of the ego-motion estimation, in order to obtain both position and velocity of the UAV relative to the landing pad. After briefly reviewing existing algorithm for the discrete case, we present, in a unified geometric framework, a new estimation scheme for solving the differential case. We further show how the obtained algorithms enable the vision sensor to be placed in the feedback loop as a state observer for landing control. These algorithms are linear, numerically robust, and computationally inexpensive hence suitable for real-time implementation. We present a thorough performance evaluation of the motion estimation algorithms under varying levels of image measurement noise, altitudes of the camera above the landing pad, and different camera motions relative to the landing pad. A landing controller is then designed for a full dynamic model of the UAV. Using geometric nonlinear control theory, the dynamics of the UAV are decoupled into an inner system and outer system. The proposed control scheme is then based on the differential flatness of the outer system. For the overall closed-loop system, conditions are provided under which exponential stability can be guaranteed. In the closed-loop system, the controller is tightly coupled with the vision based state estimation and the only auxiliary sensor are accelerometers for measuring acceleration of the UAV. Finally, we show through simulation results that the designed vision-in-the-loop controller generates stable landing maneuvers even for large levels of image measurement noise. Experiments on a real UAV will be presented in future work.

关键词： Motion estimation computer vision based control unmanned air vehicle differential flatness

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Matching 3D models with Global Geometric Feature Map

Matching 3D models with Global Geometric Feature Map

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12th International Multi-Media Modelling Conference

作者： Wang, Donghui Cui, Chenyang Wu, Zheng College of Computer Science Zhejiang University China Institute of Image and Graphics China Academy of Art China

ISBN: (纸本)1424400287

Measuring the similarity between 3D models is a fundamental task in 3D inodels retrieval. In this paper, we propose a new method based on Global Geometric Feature Map (GGFM) to represent arbitrary polygonal 3D models. Since 3D polygonal model can be expressed as a set of facets, the GGFM contrast constitute a spherical histogram about the normal orientation and area and position of every facet on the surface of the model. By computing the spherical correlation between the GGFMs of the matched models, similarity of two models can be obtained. Experimental results show that the proposed method performs well in 3D model similarity matching and is invariant to the translation and rotation and scaling of 3D model. Comparing to the existing methods, this method is fast and needs low computation and storage cost since each facet of the model needs to be computed only once in GGFM.

关键词： Pattern matching

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Exact crossing minimization

Exact crossing minimization

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13th International Symposium on Graph Drawing, GD 2005

作者： Buchheim, Christoph Ebner, Dietmar Jünger, Michael Klau, Gunnar W. Mutzel, Petra Weiskircher, René Department of Computer Science University of Cologne Institute of Computer Graphics and Algorithms Vienna University of Technology Department of Mathematics and Computer Science FU Berlin Department of Computer Science University of Dortmund CSIRO Mathematical and Information Sciences

ISBN: (纸本)3540314253

The crossing number of a graph is the minimum number of edge crossings in any drawing of the graph into the plane. This very basic property has been studied extensively in the literature from a theoretic point of view and many bounds exist for a variety of graph classes. In this paper, we present the first algorithm able to compute the crossing number of general sparse graphs of moderate size and present computational results on a popular benchmark set of graphs. The approach uses a new integer linear programming formulation of the problem combined with strong heuristics and problem reduction techniques. This enables us to compute the crossing number for 91 percent of all graphs on up to 40 nodes in the benchmark set within a time limit of five minutes per graph. © Springer-Verlag Berlin Heidelberg 2005.

关键词： Graph theory

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Development of the ATC simulators

Development of the ATC simulators

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16th International Conference on Artificial Reality and Telexistence - Workshops, ICAT 2006

作者： Shi-feng, Mo Hui, Li Xian-jiang, He Zhi-sheng, You Institute of Graphics and Images School of Computer Science and Engineering Sichuan University Chengdu 610065 China

ISBN: (纸本)076952754X

In the ATC domain, simulated training is an effective approach to cultivate controllers, and ATC simulators providing vivid simulated environment for the trainees are the key devices with high complexity. In this paper, the software product line approach is proposed to build a group of ATC simulators from a common set of core assets. As the core assets shared across our ATC simulators, the high-level procedural model, architecture, real-time network communication component, primitive-based aerostats' operation command mechanism and multi-PC based 3D virtual scene rendering system are analyzed and described in detail, which is helpful to the development of other similar simulation applications. Additionally, the development of a tower simulator is presented as an example with a few screenshots, which shows our solution is effective and helpful to the complex simulation applications family such as ATC simulators. © 2006 IEEE.

关键词： Simulators

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A concise functional neural network for computing the extremum eigenpairs of real symmetric matrices

A concise functional neural network for computing the extrem...

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3rd International Symposium on Neural Networks, ISNN 2006 - Advances in Neural Networks

作者： Liu, Yiguang You, Zhisheng Institute of Image and Graphics School of Computer Science and Engineering Sichuan University Chengdu 610064 China

ISBN: (纸本)354034439X

Quick extraction of the extremum eigenpairs of a real symmetric matrix is very important in engineering. Using neural networks to complete this operation is in a parallel manner and can achieve high performance. So, this paper proposes a very concise functional neural network (FNN) to compute the largest (or smallest) eigenvalue and one corresponding eigenvector. After transforming the FNN into a differential equation, and obtaining the analytic solution, the convergence properties are completely analyzed. By this FNN, the method that can compute the extremum eigenpairs whether the matrix is non-definite, positive definite or negative definite is designed. Finally, three examples show the validity. Comparing with the other ones used in the same field, the proposed FNN is very simple and concise, so it is very easy to realize. © Springer-Verlag Berlin Heidelberg 2006.

关键词： Neural networks

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Near Optimal Hierarchical Culling: Performance Driven Use of Hardware Occlusion Queries

Near Optimal Hierarchical Culling: Performance Driven Use of...

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17th Eurographics Symposium on Rendering Techniques, EGSR 2006

作者： Guthe, Michael Balázs, Ákos Klein, Reinhard Institute for Computer Science II Universität Bonn Germany

ISBN: (纸本)3905673355

The most efficient general occlusion culling techniques are based on hardware accelerated occlusion queries. Although in many cases these techniques can considerably improve performance, they may still reduce efficiency compared to simple view frustum culling, especially in the case of low depth complexity. This prevented the broad use of occlusion culling in most commercial applications. In this paper we present a new conservative method to solve this problem, where the main idea is to use a statistical model describing the occlusion probability for each occlusion query in order to reduce the number of wasted queries which are the reason for the reduction in rendering speed. We also describe an abstract parameterized model for the graphics hardware performance. The parameters are easily measurable at startup and thus the model can be adapted to the graphics hardware in use. Combining this model with the estimated occlusion probability our method is able to achieve a near optimal scheduling of the occlusion queries. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures. © The Eurographics Association 2006.

关键词： Rendering (computer graphics)

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Coating application method and calendering influence on the spatial coating layer formation obtained by an automated serical sectioning method

Coating application method and calendering influence on the ...

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2006 TAPPI Advanced Coating Fundamentals Symposium

作者： Wiltsche, M. Bauer, W. Donoser, M. Institute for Paper Pulp and Fiber Technology - IPZ Graz University of Technology Kopernikusgasse 24/II Austria Institute for Computer Graphics and Vision - ICG Graz University of Technology Inffeldgasse 16/II Austria

After an introduction to related research in the field of spatial coating layer formation, a new analysis method, based on a fully automated microtomy process and light microscopy combined with advanced image analysis algorithms, is presented. The concept offers both, a high spatial resolution and a significantly larger sample size than conventional SEM techniques. The concept is based on a light microscope which is attached to a rotary microtome. An embedded paper sample is digitized by means of serial sectioning. Repeatedly, slices are cut off the embedded paper sample and the cut block surface is scanned fully automated. Image analysis software was developed to automatically detect the coating layer. Segmentation of the coating layer is realized by a 3D color segmentation process in the RGB color space instead of a threshold based algorithm. The approach itself is a three-dimensional concept, meaning that for the detection of the coating layer in one slice image also data from the neighboring slices is incorporated. Thus, the algorithm delivers both, detailed and robust coating layer recognition. Single coated LWC papers from a pilot coater were analyzed to compare coating layer formation for blade and curtain coating. Local correlation was used to study the relation between the obtained thickness and topography values of the base paper and the coating layers for both coating methods. The results showed, as expected, in tendency a leveling coat behavior for blade coating and a contour coat behavior for curtain coating. However, especially the curtain coated sample, but also the blade coated sample, was away from the idealized characteristics of a contour or a leveling coat respectively. Studies regarding the effect of calendering on these samples showed that calendering predominantly influences the base sheet topography under the coating layer with a less pronounced effect on the coating layer thickness.

关键词： Coating techniques

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GPU-ABiSort: Optimal parallel sorting on stream architectures 20

GPU-ABiSort: Optimal parallel sorting on stream architecture...

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20th IEEE International Parallel and Distributed Processing Symposium, IPDPS 2006

作者： Greß, Alexander Zachmann, Gabriel Institute of Computer Science II Rhein. Friedr.-Wilh.-Universität Bonn Bonn Germany Institute of Computer Science Clausthal University of Technology Clausthal Germany

ISBN: (纸本)1424400546

In this paper, we present a novel approach for parallel sorting on stream processing architectures. It is based on adaptive bitonic sorting. For sorting n values utilizing p stream processor units, this approach achieves the optimal time complexity O((n log n)/p). While this makes our approach competitive with common sequential sorting algorithms not only from a theoretical viewpoint, it is also very fast from a practical viewpoint. This is achieved by using efficient linear stream memory accesses (and by combining the optimal time approach with algorithms optimized for small input sequences). We present an implementation on modern programmable graphics hardware (GPUs). On recent GPUs, our optimal parallel sorting approach has shown to be remarkably faster than sequential sorting on the CPU, and it is also faster than previous non-optimal sorting approaches on the GPU for sufficiently large input sequences. Because of the excellent scalability of our algorithm with the number of stream processor units p (up to n/ log2n or even n/log n units, depending on the stream architecture), our approach profits heavily from, the trend of increasing number of fragment processor units on GPUs, so that we can expect further speed improvement with upcoming GPU generations. © 2006 IEEE.

关键词： Parallel processing systems

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Visualization aspects in the MERCW project

Visualization aspects in the MERCW project

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IEEE US/EU Baltic International Symposium, BALTIC 2006

作者： Borodin, P. Greß, A. Klein, R. University of Bonn Institute of Computer Science II Römerstraße 164 Bonn53117 Germany

ISBN: (纸本)9781509002122

The MERCW project focuses on the study of chemical munition dump sites in the Baltic Sea and Skagerrak area. Through focused site investigations an assessment will be made of the ecological risks related to the dumped warfare for the marine ecosystem and people. One of the objectives of the project is to illustrate the results from the risk assessment using innovative visualization techniques. Our aim is to develop technology to interactively analyze and explore data that is collected, simulated, and used in the project, in order to support decision-making, risk analysis, and emergency plans. The data to be considered will include detailed bathymetric maps of the sea bottom, different scalar fields defined on the 3D water volume (e.g. temperature, salinity, and concentrations of poisonous substances) as well as vector fields (e.g. sea currents). In order to achieve this goal we will apply and enhance well-established methods of terrain, volume, and flow visualization. Special emphasis will be put on fast techniques that exploit the parallel computing power of current graphics processing units (GPUs). In addition to common visualization techniques, stereo rendering in virtual environments, such as PowerWall and CAVE, will further enhance the perception and understanding of complex 3D phenomena. © 2006 IEEE.

关键词： Risk assessment

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Free-form modelling for surface inpainting 06

Free-form modelling for surface inpainting

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4th International Conference on computer graphics, Virtual Reality, Visualisation and Interaction in Africa, Afrigaph '06

作者： Bendels, Gerhard H. Guthe, Michael Klein, Reinhard Universität Bonn Institute of Computer Science II Römerstraße 164 53117 Bonn Germany

ISBN: (纸本)1595932887

In this paper, we describe a novel approach to 3D shape modelling, targeting at the reconstruction and repair of digitised models - a task that is frequently encountered in particular in the fields of cultural heritage and archaeology. In these fields, faithfully digitised models are often to be restorated in order to visualise the object in its original state, reversing the effects of aging or decay. In our approach, we combine intuitive free-form modelling techniques with automatic 3D surface completion to derive a powerful modelling methodology that on the one hand is capable of including a user's expertise into the surface completion process. The automatic completion, on the other hand, reconstructs the required surface detail in the modelled region and thus frees the user from the need to model every last detail manually. The power and feasibility of our approach is demonstrated with several examples. Copyright © 2006 by the Association for Computing Machinery, Inc.

关键词： computer graphics

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