共查询到20条相似文献,搜索用时 46 毫秒
1.
Daisuke Miyazaki Takushi Shibata Katsushi Ikeuchi 《International Journal of Computer Vision》2010,86(2-3):171-191
In order to create a photorealistic Virtual Reality model, we have to record the appearance of the object from different directions under different illuminations. In this paper, we propose a method that renders photorealistic images from a small amount of data. First, we separate the images of the object into a diffuse reflection component and a specular reflection component by using linear polarizers. Then, we estimate the parameters of the reflection model for each component. Finally, we compress the difference between the input images and the rendered images by using wavelet transform. At the rendering stage, we first calculate the diffuse and specular reflection images from the reflection parameters, then add the difference decompressed by inverse wavelet transform into the calculated reflection images, and finally obtain the photorealistic image of the object. 相似文献
2.
In practice, the clearances of joints in a great number of mechanical systems are well under control. In these cases, some
of the existing methods become unpractical because of the little differences in the order of magnitude between relative movements
and computational errors. Assuming that the effects of impacts are negligible, we proved that both locations and forces of
contacts in joints can be fully determined by parts of joint reaction forces. Based on this fact, a method particularly suited
for multibody systems possessing frictional joints with tiny clearances is presented. In order to improve the efficiency of
computation, recursive formulations are proposed based on the interactions between bodies. The proposed recursive formulations
can improve the computation of joint reaction forces. With the methodology presented in this paper, not only the motion of
bodies in a multibody system but also the details about the contacts in joints, such as forces of contacts and locations of
contact points, can be obtained. Even with the assumption of impact free, the instants of possible impacts can be detected
without relying upon any ambiguous parameters, as indicated by numerical examples in this paper. 相似文献
3.
Ian M. Mitchell 《Journal of scientific computing》2008,35(2-3):300-329
Level set methods are a popular and powerful class of numerical algorithms for dynamic implicit surfaces and solution of Hamilton-Jacobi PDEs. While the advanced level set schemes combine both efficiency and accuracy, their implementation complexity makes it difficult for the community to reproduce new results and make quantitative comparisons between methods. This paper describes the Toolbox of Level Set Methods, a collection of Matlab routines implementing the basic level set algorithms on fixed Cartesian grids for rectangular domains in arbitrary dimension. The Toolbox’s code and interface are designed to permit flexible combinations of different schemes and PDE forms, allow easy extension through the addition of new algorithms, and achieve efficient execution despite the fact that the code is entirely written as m-files. The current contents of the Toolbox and some coding patterns important to achieving its flexibility, extensibility and efficiency are briefly explained, as is the process of adding two new algorithms. Code for both the Toolbox and the new algorithms is available from the Web. 相似文献
4.
For many years, the hidden Markov model (HMM) has been one of the most popular tools for analysing sequential data. One frequently used special case is the left-right model, in which the order of the hidden states is known. If knowledge of the duration of a state is available it is not possible to represent it explicitly with an HMM. Methods for modelling duration with HMM’s do exist (Rabiner in Proc. IEEE 77(2):257–286, [1989]), but they come at the price of increased computational complexity. Here we present an efficient and robust algorithm for modelling duration in HMM’s, and this algorithm is successfully used to control autonomous computer actors in a theatrical play. 相似文献
5.
This paper discusses the navigation, guidance and control (NGC) system of an Unmanned Surface Vehicle (USV) through extended
at sea trials carried out with the prototype autonomous catamaran Charlie. In particular, experiments demonstrate the effectiveness,
both for precision and power consumption, of extended Kalman filter and simple PID guidance and control laws to perform basic
control tasks such as auto-heading, auto-speed and straight line following with a USV equipped only with GPS and compass.
相似文献
Gabriele BruzzoneEmail: |
6.
Ishay Goldin Jean-Marc Delosme Alfred M. Bruckstein 《Journal of Mathematical Imaging and Vision》2010,37(2):112-131
Modeling the deformation of shapes under constraints on both perimeter and area is a challenging task due to the highly nontrivial
interaction between the need for flexible local rules for manipulating the boundary and the global constraints. We propose
several methods to address this problem and generate “random walks” in the space of shapes obeying quite general possibly
time varying constraints on their perimeter and area. Design of perimeter and area preserving deformations are an interesting
and useful special case of this problem. The resulting deformation models are employed in annealing processes that evolve
original shapes toward shapes that are optimal in terms of boundary bending-energy or other functionals. Furthermore, such
models may find applications in the analysis of sequences of real images of deforming objects obeying global constraints as
building blocks for registration and tracking algorithms. 相似文献
7.
Eiichi Yoshida Mathieu Poirier Jean-Paul Laumond Oussama Kanoun Florent Lamiraux Rachid Alami Kazuhito Yokoi 《Autonomous Robots》2010,28(1):77-88
In this paper we address whole-body manipulation of bulky objects by a humanoid robot. We adopt a “pivoting” manipulation
method that allows the humanoid to displace an object without lifting, but by the support of the ground contact. First, the
small-time controllability of pivoting is demonstrated. On its basis, an algorithm for collision-free pivoting motion planning
is established taking into account the naturalness of motion as nonholonomic constraints. Finally, we present a whole-body
motion generation method by a humanoid robot, which is verified by experiments. 相似文献
8.
In this paper we continue the study, which was initiated in (Ben-Artzi et al. in Math. Model. Numer. Anal. 35(2):313–303,
2001; Fishelov et al. in Lecture Notes in Computer Science, vol. 2667, pp. 809–817, 2003; Ben-Artzi et al. in J. Comput. Phys. 205(2):640–664, 2005 and SIAM J. Numer. Anal. 44(5):1997–2024, 2006) of the numerical resolution of the pure streamfunction formulation of the time-dependent two-dimensional Navier-Stokes equation.
Here we focus on enhancing our second-order scheme, introduced in the last three afore-mentioned articles, to fourth order
accuracy. We construct fourth order approximations for the Laplacian, the biharmonic and the nonlinear convective operators.
The scheme is compact (nine-point stencil) for the Laplacian and the biharmonic operators, which are both treated implicitly
in the time-stepping scheme. The approximation of the convective term is compact in the no-leak boundary conditions case and
is nearly compact (thirteen points stencil) in the case of general boundary conditions. However, we stress that in any case
no unphysical boundary condition was applied to our scheme. Numerical results demonstrate that the fourth order accuracy is
actually obtained for several test-cases. 相似文献
9.
In this paper, a new lattice Boltzmann model based on the rebuilding-divergency method for the Poisson equation is proposed.
In order to translate the Poisson equation into a conservation law equation, the source term and diffusion term are changed
into divergence forms. By using the Chapman-Enskog expansion and the multi-scale time expansion, a series of partial differential
equations in different time scales and several higher-order moments of equilibrium distribution functions are obtained. Thus,
by rebuilding the divergence of the source and diffusion terms, the Laplace equation and the Poisson equation with the second
accuracy of the truncation errors are recovered. In the numerical examples, we compare the numerical results of this scheme
with those obtained by other classical method for the Green-Taylor vortex flow, numerical results agree well with the classical
ones. 相似文献
10.
Given a data set in a metric space, we study the problem of hierarchical clustering to minimize the maximum cluster diameter,
and the hierarchical k-supplier problem with customers arriving online.
We prove that two previously known algorithms for hierarchical clustering, one (offline) due to Dasgupta and Long and the
other (online) due to Charikar, Chekuri, Feder and Motwani, output essentially the same result when points are considered
in the same order. We show that the analyses of both algorithms are tight and exhibit a new lower bound for hierarchical clustering.
Finally we present the first constant factor approximation algorithm for the online hierarchical k-supplier problem. 相似文献
11.
A Bilinear Approach to the Parameter Estimation of a General Heteroscedastic Linear System,with Application to Conic Fitting 总被引:3,自引:1,他引:2
In this paper, we employ low-rank matrix approximation to solve a general parameter estimation problem: where a non-linear
system is linearized by treating the carrier terms as separate variables, thereby introducing heteroscedastic noise. We extend
the bilinear approach to handle cases with heteroscedastic noise, in the framework of low-rank approximation.
The ellipse fitting problem is investigated as a specific example of the general theory. Despite the impression given in the
literature, the ellipse fitting problem is still unsolved when the data comes from a small section of the ellipse. Although
there are already some good approaches to the problem of ellipse fitting, such as FNS and HEIV, convergence in these iterative
approaches is not ensured, as pointed out in the literature. Another limitation of these approaches is that they cannot model
the correlations among different rows of the “general measurement matrix”. Our method, of employing the bilinear approach
to solve the general heteroscedastic parameter estimation problem, overcomes these limitations: it is convergent, at least
to a local optimum, and can cope with a general heteroscedastic problem. Experiments show that the proposed bilinear approach
performs better than other competing approaches: although it is still far short of a solution when the data comes from a very
small arc of the ellipse.
相似文献
Pei ChenEmail: |
12.
Alexander M. Bronstein Michael M. Bronstein Alfred M. Bruckstein Ron Kimmel 《International Journal of Computer Vision》2009,84(2):163-183
Similarity is one of the most important abstract concepts in human perception of the world. In computer vision, numerous applications
deal with comparing objects observed in a scene with some a priori known patterns. Often, it happens that while two objects are not similar, they have large similar parts, that is, they are
partially similar. Here, we present a novel approach to quantify partial similarity using the notion of Pareto optimality.
We exemplify our approach on the problems of recognizing non-rigid geometric objects, images, and analyzing text sequences. 相似文献
13.
In this analytical study we derive the optimal unbiased value estimator (MVU) and compare its statistical risk to three well
known value estimators: Temporal Difference learning (TD), Monte Carlo estimation (MC) and Least-Squares Temporal Difference
Learning (LSTD). We demonstrate that LSTD is equivalent to the MVU if the Markov Reward Process (MRP) is acyclic and show
that both differ for most cyclic MRPs as LSTD is then typically biased. More generally, we show that estimators that fulfill
the Bellman equation can only be unbiased for special cyclic MRPs. The reason for this is that at each state the bias is calculated
with a different probability measure and due to the strong coupling by the Bellman equation it is typically not possible for
a set of value estimators to be unbiased with respect to each of these measures. Furthermore, we derive relations of the MVU
to MC and TD. The most important of these relations is the equivalence of MC to the MVU and to LSTD for undiscounted MRPs
in which MC has the same amount of information. In the discounted case this equivalence does not hold anymore. For TD we show that it is essentially unbiased for acyclic
MRPs and biased for cyclic MRPs. We also order estimators according to their risk and present counter-examples to show that
no general ordering exists between the MVU and LSTD, between MC and LSTD and between TD and MC. Theoretical results are supported
by examples and an empirical evaluation. 相似文献
14.
Cloud Computing refers to the notion of outsourcing on-site available services, computational facilities, or data storage
to an off-site, location-transparent centralized facility or “Cloud.” Gang Scheduling is an efficient job scheduling algorithm
for time sharing, already applied in parallel and distributed systems. This paper studies the performance of a distributed
Cloud Computing model, based on the Amazon Elastic Compute Cloud (EC2) architecture that implements a Gang Scheduling scheme.
Our model utilizes the concept of Virtual Machines (or VMs) which act as the computational units of the system. Initially,
the system includes no VMs, but depending on the computational needs of the jobs being serviced new VMs can be leased and
later released dynamically. A simulation of the aforementioned model is used to study, analyze, and evaluate both the performance
and the overall cost of two major gang scheduling algorithms. Results reveal that Gang Scheduling can be effectively applied
in a Cloud Computing environment both performance-wise and cost-wise. 相似文献
15.
Communication and coordination are the main cores for reaching a constructive agreement among multi-agent systems (MASs). Dividing the overall performance of MAS to individual agents may lead to group learning as opposed to individual learning, which is one of the weak points of MASs. This paper proposes a recursive genetic framework for solving problems with high dynamism. In this framework, a combination of genetic algorithm and multi-agent capabilities is utilised to accelerate team learning and accurate credit assignment. The argumentation feature is used to accomplish agent learning and the negotiation features of MASs are used to achieve a credit assignment. The proposed framework is quite general and its recursive hierarchical structure could be extended. We have dedicated one special controlling module for increasing convergence time. Due to the complexity of blackjack, we have applied it as a possible test bed to evaluate the system’s performance. The learning rate of agents is measured as well as their credit assignment. The analysis of the obtained results led us to believe that our robust framework with the proposed negotiation operator is a promising methodology to solve similar problems in other areas with high dynamism. 相似文献
16.
In this paper, the Minimum Polynomial Extrapolation method (MPE) is used to accelerate the convergence of the Characteristic–Based–Split
(CBS) scheme for the numerical solution of steady state incompressible flows with heat transfer. The CBS scheme is a fractional
step method for the solution of the Navier–Stokes equations while the MPE method is a vector extrapolation method which transforms
the original sequence into another sequence converging to the same limit faster then the original one without the explicit
knowledge of the sequence generator. The developed algorithm is tested on a two-dimensional benchmark problem (buoyancy–driven
convection problem) where the Navier–Stokes equations are coupled with the temperature equation. The obtained results show
the feature of the extrapolation procedure to the CBS scheme and the reduction of the computational time of the simulation. 相似文献
17.
Christophe Vandekerckhove Ioannis Kevrekidis Dirk Roose 《Journal of scientific computing》2009,39(2):167-188
The long-term dynamic behavior of many dynamical systems evolves on a low-dimensional, attracting, invariant slow manifold,
which can be parameterized by only a few variables (“observables”). The explicit derivation of such a slow manifold (and thus,
the reduction of the long-term system dynamics) is often extremely difficult or practically impossible. For this class of
problems, the equation-free framework has been developed to enable performing coarse-grained computations, based on short
full model simulations. Each full model simulation should be initialized so that the full model state is consistent with the
values of the observables and close to the slow manifold. To compute such an initial full model state, a class of constrained
runs functional iterations was proposed (Gear and Kevrekidis, J. Sci. Comput. 25(1), 17–28, 2005; Gear et al., SIAM J. Appl. Dyn. Syst. 4(3), 711–732, 2005). The schemes in this class only use the full model simulator and converge, under certain conditions, to an approximation
of the desired state on the slow manifold. In this article, we develop an implementation of the constrained runs scheme that
is based on a (preconditioned) Newton-Krylov method rather than on a simple functional iteration. The functional iteration
and the Newton-Krylov method are compared in detail using a lattice Boltzmann model for one-dimensional reaction-diffusion
as the full model simulator. Depending on the parameters of the lattice Boltzmann model, the functional iteration may converge
slowly or even diverge. We show that both issues are largely resolved by using the Newton-Krylov method, especially when a
coarse grid correction preconditioner is incorporated. 相似文献
18.
We first present a method to rule out the existence of parameter non-increasing polynomial kernelizations of parameterized
problems under the hypothesis P≠NP. This method is applicable, for example, to the problem Sat parameterized by the number of variables of the input formula. Then we obtain further improvements of corresponding results
in (Bodlaender et al. in Lecture Notes in Computer Science, vol. 5125, pp. 563–574, Springer, Berlin, 2008; Fortnow and Santhanam in Proceedings of the 40th ACM Symposium on the Theory of Computing (STOC’08), ACM, New York, pp. 133–142,
2008) by refining the central lemma of their proof method, a lemma due to Fortnow and Santhanam. In particular, assuming that
the polynomial hierarchy does not collapse to its third level, we show that every parameterized problem with a “linear OR”
and with NP-hard underlying classical problem does not have polynomial self-reductions that assign to every instance x with parameter k an instance y with |y|=k
O(1)⋅|x|1−ε
(here ε is any given real number greater than zero). We give various applications of these results. On the structural side we prove
several results clarifying the relationship between the different notions of preprocessing procedures, namely the various
notions of kernelizations, self-reductions and compressions. 相似文献
19.
Alireza Pourshahid Daniel Amyot Liam Peyton Sepideh Ghanavati Pengfei Chen Michael Weiss Alan J. Forster 《Electronic Commerce Research》2009,9(4):269-316
A number of recent initiatives in both academia and industry have sought to achieve improvements in e-businesses through the
utilization of Business Process Management (BPM) methodologies and tools. However there are still some inadequacies that need
to be addressed when it comes to achieving alignment between business goals and business processes. The User Requirements
Notation (URN), recently standardized by ITU-T, has some unique features and capabilities beyond what is available in other
notations that can help address alignment issues. In this paper, a URN-based framework and its supporting toolset are introduced
which provide business process monitoring and performance management capabilities integrated across the BPM lifecycle. The
framework extends the URN notation with Key Performance Indicators (KPIs) and other concepts to measure and align processes
and goals. An example process for controlling access to a healthcare data warehouse is used to illustrate and evaluate the
framework. Early results indicate the feasibility of the approach. 相似文献
20.
Emilio Di Giacomo Walter Didimo Giuseppe Liotta Henk Meijer 《Theory of Computing Systems》2011,49(3):565-575
In this paper we study non-planar drawings of graphs, and study trade-offs between the crossing resolution (i.e., the minimum
angle formed by two crossing segments), the curve complexity (i.e., maximum number of bends per edge), the total number of
bends, and the area. 相似文献