206417245
Estimation of Displacements from Two 3-D Frames Obtained From Stereo
A method for estimating 3D displacements from two stereo frames is presented. It is based on the hypothesize-and-verify paradigm used to match 3D line segments between the two frames. In order to reduce the complexity of the method, an assumption is made that objects are rigid. The formulate a set of complete rigidity constraints for 3D line segments and integrate the uncertainty of measurements in this formation. The hypothesize-and-verify stages of the method use an extended Kalman filter to produce estimates of the displacements and of their uncertainty. The algorithm is shown to work on indoor and natural scenes. It is also shown to be easily extended to the case in which several mobile objects are present. The method is quite robust, fast, and has been thoroughly tested on hundreds of real stereo frames. >
29303828
Parameter estimation techniques: a tutorial with application to conic fitting
Almost all problems in computer vision are related in one form or another to the problem of estimating parameters from noisy data. In this tutorial, we present what is probably the most commonly used techniques for parameter estimation. These include linear least-squares (pseudo-inverse and eigen analysis); orthogonal least-squares; gradient-weighted least-squares; bias-corrected renormalization; Kalman filtering; and robust techniques (clustering, regression diagnostics, M-estimators, least median of squares). Particular attention has been devoted to discussions about the choice of appropriate minimization criteria and the robustness of the different techniques. Their application to conic fitting is described.
16882965
The performance of the cedar multistage switching network
While multistage switching networks for vector multiprocessors have been studied extensively, detailed evaluations of their performance are rare. Indeed, analytical models, simulations with pseudo-synthetic loads, studies focused on average-value parameters, and measurements of networks disconnected from the machine, all provide limited information. In this paper, instead, we present an in-depth empirical analysis of a multistage switching network in a realistic setting: we use hardware probes to examine the performance of the omega network of the Cedar shared-memory machine executing real applications. The machine is configured with 16 vector processors.The analysis suggests that the performance of multistage switching networks is limited by traffic non-uniformities. We identify two major non-uniformities that degrade Cedar's performance and are likely to slow down other networks too. The first one is the contention caused by the return messages in a vector access as they converge from the memories to one processor port. This traffic convergence penalizes vector reads and, more importantly, causes tree saturation. The second non-uniformity is the uneven contention delays induced by even a relatively fair scheme to resolve message collisions. Based on our observations, we argue that intuitive optimizations for multistage switching networks may not be cost-effective. Instead, we suggest changes to increase the network bandwidth at the root of the traffic convergence tree and to delay traffic convergence up until the final stages of the network.
18081212
A novel analytical model for electronic and optical switches with shared buffer
Switches with shared buffer have lower packet loss probabilities than other types of switches when the sizes of the buffers are the same. In the past, the performance analysis for electronic shared buffer switches has been carried out extensively. However, due to the strong dependencies of the output queues in the buffer, it is very difficult to find a good analytical model. Existing models are either accurate but have exponential complexities or not very accurate. In this paper, we propose a novel analytical model called the aggregation model for switches with shared buffer. This model can be used for analyzing both electronic and optical switches, and has perfect accuracies under all tested conditions and has polynomial time complexity. It is based on the idea of induction: first find the behavior of 2 queues, then aggregate them into one block; then find the behavior of 3 queues while regarding 2 of the queues as one block, then aggregate the 3 queues into one block; then aggregate 4 queues and so on. When a sufficient number of queues have been aggregated, the behavior of the entire switch is found. We believe that the new model represents the best analytical model for shared buffer switches so far.
8041199
Scheduling in buffered WDM packet switching networks with arbitrary wavelength conversion capability
Optical networking is a promising candidate for high-speed communication networks because of its huge bandwidth. In this paper we study optimal scheduling in buffered WDM packet switching networks with arbitrary wavelength conversion ability. We focus on limited range wavelength conversion while considering full range wavelength conversion as a special case of it. We formalize the problem of maximizing network throughput and minimizing total delay in such a network as finding an optimal matching in a weighted bipartite graph. We then give a simple and fast algorithm called the scan and swap algorithm that solves the problem in O(kB/sup 2/) time, where k is the number of wavelengths per fiber and B is the buffer length, as compared to other existing algorithms that need at least O(k/sup 2/B/sup 2/ + k/sup 2/BN) time where N is the number of input fibers.
5888722
The transformation graph Gxyz when xyz=-++
The transformation graph G^-^+^+ of G is the graph with vertex set V(G)@?E(G) in which the vertex x and y are joined by an edge if one of the following conditions holds: (i) x,y@?V(G), and x and y are not adjacent in G, (ii) x,y@?E(G), and x and y are adjacent in G, (iii) one of x and y is in V(G) and the other is in E(G), and they are incident in G. In this paper, it is shown that for two graphs G and G^', G^-^+^+@?G^'^-^+^+ if and only if G@?G^'. Simple necessary and sufficient conditions are given for G^-^+^+ to be planar and hamiltonian, respectively. It is also shown that for a graph G, the edge-connectivity of G^-^+^+ is equal to its minimum degree. Two related conjectures and some research problems are presented.
9407873
Linear combination representation for outlier detection in motion tracking
In this paper we show that Ullman and Basri's linear combination (LC) representation, which was originally proposed for alignment-based object recognition, can be used for outlier detection in motion tracking with an affine camera. For this task LC can be realized either on image frames or feature trajectories, and therefore two methods are developed which we call linear combination of frames and linear combination of trajectories. For robust estimation of the linear combination coefficients, the support vector regression (SVR) algorithm is used and compared with the RANSAC method. SVR based on quadratic programming optimization can efficiently deal with more than 50 percent outliers and delivers more consistent results than RANSAC in our experiments. The linear combination representation can use SVR in a straightforward manner while previous factorization-based or subspace separation methods cannot. Experimental results are presented using real video sequences to demonstrate the effectiveness of our LC+SVR approaches, including a quantitative comparison of SVR and RANSAC.