scholarly journals A Global Calibration Method for Widely Distributed Cameras Based on Vanishing Features

Sensors ◽  
2016 ◽  
Vol 16 (6) ◽  
pp. 838 ◽  
Author(s):  
Xiaolong Wu ◽  
Sentang Wu ◽  
Zhihui Xing ◽  
Xiang Jia
Keyword(s):  
Calibration Method ◽  
Global Calibration ◽  
Distributed Cameras

scholarly journals Global Calibration of Multi-Cameras Based on Refractive Projection and Ray Tracing

2017 ◽  
Author(s):  
Mingchi Feng ◽  
Xiang Jia ◽  
Jingshu Wang ◽  
Song Feng ◽  
Taixiong Zheng
Keyword(s):  
Ray Tracing ◽  
Real Data ◽  
Calibration Method ◽  
Calibration Error ◽  
Multiple Cameras ◽  
Projection Model ◽  
Vision Measurement ◽  
3D Computer Vision ◽  
Global Calibration ◽  
Calibration Methods

Multi-cameras system is widely applied in 3D computer vision especially when multiple cameras are distributed on both sides of the measured object. The calibration methods of multi-cameras system are critical to the accuracy of vision measurement and the key is to find an appropriate calibration target. In this paper, a high-precision camera calibration method for multi-cameras system based on transparent glass checkerboard and ray tracing is described, which is used to calibrate multiple cameras distributed on both sides of the glass checkerboard. Firstly, the intrinsic parameters of each camera is obtained by Zhang’s calibration method. Then, multiple cameras capture several images from the front and back of the glass checkerboard with different orientations, and all images contain distinct grid corners. As the cameras on one side are not affected by the refraction of glass checkerboard, extrinsic parameters can be directly calculated. However, the cameras on another side are influenced by the refraction of glass checkerboard, and the direct use of projection model will produce calibration error. A multi-cameras calibration method using refractive projection model and ray tracing is developed to eliminate this error. Furthermore, both synthetic and real data are employed to validate the proposed approach. The experimental results of refractive calibration show that the error of the 3D reconstruction is smaller than 0.2 mm, the relative errors of both rotation and translation are less than 0.014%, and the mean and standard deviation of reprojection error of 4-cameras system are 0.00007 and 0.4543 pixel. The proposed method is flexible, high accurate, and simple to carry out.

Global or Local? A Choice for NIR Calibrations in Analyses of Forage Quality

1994 ◽  
Vol 2 (3) ◽  
pp. 163-175 ◽  
Author(s):  
G. Sinnaeve ◽  
P. Dardenne ◽  
R. Agneessens
Keyword(s):  
Scatter Correction ◽  
Forage Quality ◽  
Calibration Method ◽  
Local Regression ◽  
Global Calibration ◽  
Grass Hay ◽  
Data Points ◽  
Tropical Forages ◽  
Pre Treatment ◽  
Whole Plants

This paper investigates the effect of spectral data pre-treatment by using scatter correction techniques, detrending and derivatives on the standard error of NIR predictive models. It is shown that no particular spectral pre-treatment or no single derivative works best for the three constituents (protein, cellulose, organic matter digestibility) of the three forage databases which we investigated (grass-hay, tropical forages, maize whole plants). The best analytical results are obtained with SNVD, MSC or WMSC treatments. The best results are obtained with a first or second derivative with a segment and a gap of five data points. Local Regression was investigated for the prediction of forage quality. The standard errors of prediction were compared with those obtained with the best global calibration. Trial and error is the only way to fix the number of samples in the subset and the number of terms to retain in the model. Compared to the results for the traditional universal calibration method, the gain in SEP for protein, cellulose and digestibility in grass-hay, tropical forages or maize ranges between 5 and 11%.

Research on global calibration method for multi-camera visual measurement system

2016 ◽  
Author(s):  
Dongzhao Huang ◽  
Qiancheng Zhao ◽  
Yun Ou ◽  
Tianlong Yang
Keyword(s):  
Measurement System ◽  
Calibration Method ◽  
Visual Measurement ◽  
Global Calibration

scholarly journals Global Calibration Method of a Camera Using the Constraint of Line Features and 3D World Points

2016 ◽  
Vol 16 (4) ◽  
pp. 190-196 ◽  
Author(s):  
Guan Xu ◽  
Xinyuan Zhang ◽  
Xiaotao Li ◽  
Jian Su ◽  
Zhaobing Hao
Keyword(s):  
Calibration Method ◽  
Original Method ◽  
Transformation Matrix ◽  
Mean Values ◽  
Global Calibration ◽  
The Stability ◽  
Stability And Accuracy ◽  
Value Decomposition ◽  
Projective Lines ◽  
Mean Square Errors

Abstract We present a reliable calibration method using the constraint of 2D projective lines and 3D world points to elaborate the accuracy of the camera calibration. Based on the relationship between the 3D points and the projective plane, the constraint equations of the transformation matrix are generated from the 3D points and 2D projective lines. The transformation matrix is solved by the singular value decomposition. The proposed method is compared with the point-based calibration to verify the measurement validity. The mean values of the root-mean-square errors using the proposed method are 7.69×10−4, 6.98×10−4, 2.29×10−4, and 1.09×10−3 while the ones of the original method are 8.10×10−4, 1.29×10−2, 2.58×10−2, and 8.12×10−3. Moreover, the average logarithmic errors of the calibration method are evaluated and compared with the former method in different Gaussian noises and projective lines. The variances of the average errors using the proposed method are 1.70×10−5, 1.39×10−4, 1.13×10−4, and 4.06×10−4, which indicates the stability and accuracy of the method.

scholarly journals Global Measurement Method for Large-Scale Components Based on a Multiple Field of View Combination

2017 ◽  
Vol 2017 ◽  
pp. 1-12 ◽  
Author(s):  
Yang Zhang ◽  
Wei Liu ◽  
Zhiguang Lan ◽  
Zhiyuan Zhang ◽  
Fan Ye ◽  
...  
Keyword(s):  
Measurement System ◽  
Measurement Method ◽  
Large Scale ◽  
Vision System ◽  
Calibration Method ◽  
Field Of View ◽  
Surface Measurement ◽  
Global Calibration ◽  
Multiple Field ◽  
Measurement Efficiency

Considering the limited measurement range of a machine vision method for the three-dimensional (3D) surface measurement of large-scale components, a noncontact and flexible global measurement method combining a multiple field of view (FOV) is proposed in this paper. The measurement system consists of two theodolites and a binocular vision system with a transfer mark. The process of multiple FOV combinations is described, and a new global calibration method is proposed to solve the coordinate system unification issue of different instruments in the measurement system. In addition, a high-precision image acquisition method, which is based on laser stripe scanning and centre line extraction, is discussed to guarantee the measurement efficiency. With the measured 3D data, surface reconstruction of large-scale components is accomplished by data integration. Experiments are also conducted to verify the precision and effectiveness of the global measurement method.

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