scholarly journals Some Model Assisted Estimators Using Functional Form Calibration Approach

Author(s):  
Naila Alam ◽  
Muhammad Hanif

The Model assisted estimators are approximately design unbiased, consistent and provides robustness in the case of large sample sizes. The model assisted estimators result in reduction of the design variance if underlying model reasonably defines the regression relationship.  If the model is misspecified, then model assisted estimators might result in an increase of the design variance but remain approximately design unbiased and show robustness against model-misspecification. The well-known model assisted estimators, generalized regression estimators are members of a larger class of calibration estimators. Calibration method generates calibration weights that meet the calibration constraints and have minimum distance from the sampling design weights. By using different distance measures, classical calibration approach generates different calibration estimators but with asymptotically identical properties. The constraint of distance minimization was reduced for studying the properties of calibration estimators by proposing a simple functional form approach. The approach generates calibration weights that prove helpful to control the changes in calibration weights by using different choices of auxiliary variable’s functions.  This paper is an extended work on model assisted approach by using functional form of calibration weights. Some new model assisted estimators are considered to get efficient and stabilized regression weights by introducing a control matrix. The asymptotic un-biasedness of the proposed estimators is verified and the expressions for MSE are derived in three different cases.  A simulation study is done to compare and evaluate the efficiency of the proposed estimators with some existing model assisted estimators.

2015 ◽  
Vol 03 (04) ◽  
pp. 277-290 ◽  
Author(s):  
Han Wang ◽  
Wei Mou ◽  
Xiaozheng Mou ◽  
Shenghai Yuan ◽  
Soner Ulun ◽  
...  

Stereo rig with wide baseline is necessary when accurate depth estimation for distant object is desired. However, in order to make calibration pattern to be viewed from both left and right cameras, the wider the baseline the bigger the calibration pattern is required. In contrast to the traditional stereo calibration method using calibration pattern, we propose a self-calibration approach that can estimate cameras' rotation matrices for stereo rig with wide baseline (3 m). Given images taken from left and right cameras, the relative roll and pitch angles between two cameras are recovered by aligning sea horizon in left and right images. The pitch angle is estimated by making the projections of one point at infinite distance appear at the same location in both images. A photometric minimization is applied to refine the rotation parameters. Compared with conventional checkerboard-based calibration techniques which require extra equipments or personnel, our approach only needs a pair of sea images. Moreover, unlike most self-calibration approaches, feature detection and matching are not required which makes it possible to apply our approach on featureless images. As a result, it is flexible and easy to implement our approach on sea surface images. Real world experiments demonstrate the feasibility of our approach.


Author(s):  
Francisco L. Silva-Gonza´lez

A calibration method which uses the so-called inverse FORM approach is proposed. The objective is to find the design point on a hypersphere in U-space, whose radius is the target reliability index, which maximizes the response that the structural system must withstand. Once the design point is determined, the safety factors can be calculated. It is demonstrated that the computational cost of the proposed method is less than the computational cost of traditional calibration techniques. The proposed method is illustrated by means of three examples: parabolic, Eurocode and suction caisson design equations.


2019 ◽  
Vol 10 (11) ◽  
pp. 2020-2033
Author(s):  
Rubén Cabrera ◽  
Jhoana Díaz-Larrea ◽  
Schery Umanzor ◽  
Laura Georgina Núñez García

2018 ◽  
Vol 29 (2) ◽  
pp. 353-371 ◽  
Author(s):  
William A. Barnett ◽  
Neepa B. Gaekwad

Author(s):  
Jianqiao Yu ◽  
Jian Lu ◽  
Yi Sun ◽  
Jishun Liu ◽  
Kai Cheng

Abstract Precise alignment of the system scan geometry is crucial to ensure the reconstructed image quality in the cone-beam CT system. A calibration method that depends on the local feature of ball bearings phantom and point-like markers is probably affected by local image variations. Besides, multiple projections with circular scanning are usually required by this type of method to derive misaligned parameters. In contrast to previous works, this paper proposes a method that depends on the global symmetric low-rank feature of a novel phantom, which can accurately represent the system geometrical misalignment. All the misaligned parameters of the cone-beam CT system can be estimated from a single perspective direction without circular scanning. Meanwhile, since the global low-rank feature of the phantom is utilized, the proposed method is robust to the noise. Extensive simulations and real experiments validate the accuracy and robustness of our method, which achieves better performance compared to an existing phantom-based method.


2010 ◽  
Vol 139-141 ◽  
pp. 2162-2167
Author(s):  
Tian Qin Wang ◽  
Chang Liu ◽  
Zhen Pu Zhang ◽  
Da Cheng Wang

This paper offers a robot calibration approach based on the virtual closed kinematic chain so that the absolute location accuracy of a robot can be improved. The calibration approach suggests that laser beam can be mounted on the robot’s end so as to form a virtual closed kinematic chain in the interest of enlarging the pose errors to proper extent, in this way straight line equations in space can be acquired when the robot positions are changed continuously, in the end the robots’ kinematic parameters can be figured out by genetic algorithm while measurement can be totally avoided in the calibration. Calibrating practices, simulating analysis and experiments on robots show that the approach can improve the absolute calibrating accuracy effectively.


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