Zhang's Algorithm Research Articles

Accurate Joint Geometric Camera Calibration of Visible and Far-Infrared Cameras

This paper presents a novel joint geometric camera calibration system using a novel calibration target for a visible and a far-infrared (FIR) cameras. By using the proposed calibration target which is the two-layer structure with different combinations of thermal emission, we can stably and precisely obtain the corresponding points of the checker pattern in the calibration target from the visible and the FIR images. The simple calibration algorithm based on the well-known Zhang's algorithm can accurately estimate the camera parameters, because we can use many useful tools which contribute the accuracy. Experimental results show that the proposed calibration system enables us to easily calibrate the visible and the FIR image with high accuracy compared with an existing system. Furthermore, the proposed system can lead to develop various applications including joint image denoising, and joint image up-sampling.

Precise vehicle speed measurement for law enforcement applications based on calibrated camera with parallel standard patterns

Common VSM (vehicle speed measurement) methods lack either necessary precision and/or flexibility to be used conveniently in law enforcement applications. In this study, a new method is proposed for simultaneous camera calibration and VSM compensating for these problems. The contribution of this study is to give a solution to the degeneracy problem of the Zhang's algorithm while dealing with parallel planar patterns and using the calibration data to estimate vehicle's speed. In applications like estimating the vehicle's speed in straight roads in which the license plates are parallel to each other, the number of linearly independent equations is reduced to 2 and the method cannot be used. In this study, the degeneracy problem of the Zhang's algorithm in dealing with parallel patterns is solved. Using orthonormal properties of all rotation vectors, the number of linearly independent equations is increased from 2 to 5 and camera calibration and VSM are performed simultaneously. Results of implementing this algorithm on real images taken by law enforcement cameras show that the proposed method can estimate the vehicle's speed with a mean of errors less than 1.22 km/h and consequently is proper for law enforcement applications.

The impact of drought on ozone dry deposition over eastern Texas

Abstract Dry deposition represents a critical pathway through which ground-level ozone is removed from the atmosphere. Understanding the effects of drought on ozone dry deposition is essential for air quality modeling and management in regions of the world with recurring droughts. This work applied the widely used Zhang dry deposition algorithm to examine seasonal and interannual changes in estimated ozone dry deposition velocities and component resistances/conductances over eastern Texas during years with drought (2006 and 2011) as well as a year with slightly cooler temperatures and above average rainfall (2007). Simulated area-averaged daytime ozone dry deposition velocities ranged between 0.26 and 0.47 cm/s. Seasonal patterns reflected the combined seasonal variations in non-stomatal and stomatal deposition pathways. Daytime ozone dry deposition velocities during the growing season were consistently larger during 2007 compared to 2006 and 2011. These differences were associated with differences in stomatal conductances and were most pronounced in forested areas. Reductions in stomatal conductances under drought conditions were highly sensitive to increases in vapor pressure deficit and warmer temperatures in Zhang's algorithm. Reductions in daytime ozone deposition velocities and deposition mass during drought years were associated with estimates of higher surface ozone concentrations.

结构现场可调的点激光精密测量系统

In order to make dot laser measuring system realize precision measurement.The structure-adjustable dot laser measuring system is established.Camera's pin-hole imaging model is used.The intrinsic camera parameters of this model are got with Zhang's algorithm.Optical center angle in dot laser measure system is defined and the formula which can calculate the optical center angle with intrinsic camera parameters that have been got firstly and coordinates of laser spot is given.The mathematical model of dot laser measure system is established,and baseline length and base angle which are called structure parameters of the system are introduced.Method to calculate the structure parameters is given.Dot laser measure system does on-line measurement with the result of dot laser measuring system calibration.Experiment results show: system's measurement range is 75mm and this calibration algorithm's maximum error is no more than 0.02mm and dot laser measure system's maximum error is below 0.06mm.This calibration algorithm meets the precision measurement requirements.

An approach for extracting a small unsatisfiable core

The article addresses the problem of finding a small unsatisfiable core of an unsatisfiable CNF formula. The proposed algorithm, CoreTrimmer, iterates over each internal node d in the resolution graph that `consumes' a large number of clauses M (i.e., a large number of original clauses are present in the unsat core with the sole purpose of proving d) and attempts to prove them without the M clauses. If this is possible, it transforms the resolution graph into a new graph that does not have the M clauses at its core. CoreTrimmer can be integrated into a fixpoint framework similarly to Malik and Zhang's fix-point algorithm run_till_ fix. We call this option trim_till_fix. Experimental evaluation on a large number of industrial CNF unsatisfiable formulas shows that trim_till_fix doubles, on average, the number of reduced clauses in comparison to run_till_fix. It is also better when used as a component in a bigger system that enforces short timeouts.

Blind parametric identification of non-Gaussian FIR systems using higher order cumulants

Two approaches are introduced for the identification of linear time-invariant systems when only output data are available. The input sequences are independent and must be non-Gaussian. To estimate the parameters of the system, we use only the fourth-order cumulants of the output, which may be contaminated by an additive, zero mean, Gaussian noise of unknown variance. To measure the performance of the proposed algorithms against existing methods, we compared them with the Zhang's algorithm. Simulations verify an apparent performance of the second algorithm, compared with the first and Zhang's algorithms, in a low signal-to-noise ratio and for small data. The simulation results show that the first algorithm has the same performance compared with Zhang's one. But the second algorithm achieves better performance compared with the first and Zhang is algorithm. For validation purposes, the second algorithm is used to search for a model able to describe and simulate the data set representing the wind speed.

Variations of Zhang's Lanczos-type product method

Among the Lanczos-type product methods, which are characterized by residual polynomials p n t n that are the product of the Lanczos polynomial p n and another polynomial t n of exact degree n with t n (0)=1, Zhang's algorithm GPBiCG has the feature that the polynomials t n are implicitly built up by a pair of coupled two-term recurrences whose coefficients are chosen so that the new residual is minimized in a 2-dimensional space. There are several ways to achieve this. We discuss here alternative algorithms that are mathematically equivalent (that is, produce in exact arithmetic the same results). The goal is to find one where the ultimate accuracy of the iterates x n is guaranteed to be high and the cost is at most slightly increased.

Branch and bound on the network model

Karp and Zhang developed a general randomized parallel algorithm for solving branch and bound problems. They showed that with high probability their algorithm attained optimal speedup within a constant factor (for p⩽ n/( logn) c , where p is the number of processors, n is the “size” of the problem, and c is a constant). Ranade later simplified the analysis and obtained a better processor bound. Karp and Zhang's algorithm works on models of computation where communication cost is constant. The present paper considers the Branch and Bound problem on networks where the communication cost is high. Suppose sending a message in a p processor network takes G = O( logp) time and node expansion (defined below) takes unit time (other operations being free). Then a simple randomized algorithm is presented which is, asymptotically, nearly optimal for p = O(2 log cn ) , where c is any constant <1/3 and n is the number of nodes in the input tree with cost no greater than the cost of the optimal leaf in the tree.

Simplified function generators based on fuzzy-logic interpolation

We replace the classical procedure for recursive linear interpolation with a technique based on simple fuzzy-set logic. This approach makes it much easier to construct multi-input interpolation procedures. The resulting function generators produce the same output as the classical formulas with slightly fewer CPU cycles if we precompute and store some coefficients before the simulation. Lin and Zhang's algorithm [K.-C. Lin, B. Zhang, Simulation 68 (3) (1997) 157–163], which precomputes and stores more interpolation-polynomial parameters, is even faster but requires much more runtime storage in the case of large function tables.

A Push/Relabel framework for submodular flows and its definement for 0-1 submodular flows

We consider the submodular flow problem of Edmonds and Giles. A submodular flow is a flow in a network satisfying capacity constraints and flow-boundary constraints given in terms of the base polyhedron of a submodular system. A cost scaling framework is constructed by using e-optimality concept associated with dual variables of a flow, originally due to Tardos and Bertsekas. The framework is a generalization of Goldberg and Tarjan's push/relabel algorithm for minimum-cost flows and also a generalization of Fujishige and Zhang's algorithm for the submodular intersection problem. Each phase of the cost scaling, called procedure Refine, improves a 2∊-optimal submodular flow to an ∊,-optimal submodular flow. Furthermore, we devise a faster hybrid algorithm of procedure Refine for the 0-1 submodular flow problem which is a natural generalization of Fujishige and Zhang's algorithm for the independent assignment problem. For a network with n vertices, m arcs and integer arc costs bounded by Г, an optimal 0-1 su...