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Ying-Ying Xu and Jiu-Nian Guan

Abstract

China is the largest swine production country in the world. The fast development has consequently brought various environmental issues which have already seriously threatened the environmental quality. This study is aimed to measure the concentrations of NH3 in the pig houses in the selected pig farm, try to conclude characteristics on the concentration change and the correlation between the concentrations and the environmental factors. The NH3 concentration was monitored in two fattening pig houses. The concentrations fluctuated between 11.0 and 26.9 ppm, 11.0 and 28.5 ppm respectively during the measurement periods, peaking at the early morning and in the afternoon before cleaning. The concentrations of NH3 correlated to the indoor temperature in winter, whereas, there was no correlation between relative humidity and NH3 concentrations.

Open access

Guan Xu, Xiaotao Li, Jian Su, Rong Chen and Jianfang Liu

A Method for the Estimation of the Square Size in the Chessboard Image using Gray-level Co-occurrence Matrix

The paper proposes a new simple procedure for measuring the square size employing the gray-level co-occurrence matrix of a chessboard image. As the size of the square structure in a chessboard image provides the geometric constraint information among the corners, it is available to improve the precision of extracting corners and serve the camera calibration. The co-occurrence matrix of a chessboard image is constructed to obtain the statistic information of the grayscale distribution. The 2D offset of the matrix is parameterized to calculate the correlation which is regarded as the implication of the repetition probability of the similar textures. A descending tendency is observed in the experiments because the similarity decreases with the greater offset. However, minimum and maximum are captured in the correlation curve, which represents that the square texture reappears with the periods of one and two square size, separately. The size of the square is tested by applying the first minimum of the correlation. The experiments are performed on the horizontal and vertical directions which are corresponding to the length and the width of the square, respectively. The experiments prove that the described method has the potential to measure square size of the chessboard.

Open access

Guan Xu, Xinyuan Zhang, Xiaotao Li, Jian Su and Zhaobing Hao

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.