Table of Content

20 March 2016, Volume 45 Issue 3

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Some Notes on Interoperability of GNSS

YANG Yuanxi, LU Mingquan, HAN Chunhao

2016, 45(3):  253-259.  doi:10.11947/j.AGCS.2016.20150653

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Compatibility and interoperability of GNSS are the hot research issues in international satellite navigation field. It is a requirement for integrated multi GNSS navigation and positioning. The basic concepts of the compatibility and interoperability are introduced and the trend of the interoperability among the GNSS providers is discussed. The status and problems of the frequency interoperability of GPS, BeiDou(BDS), GLONASS and Galileo are analyzed. It is pointed that the frequency interoperability problems will affect the manufacturers and multi GNSS users. The influences of the interoperability problems of the reference coordinate systems are not only resulted from the definitions and realizations of the reference coordinate systems but also from the maintenance and update strategies of the reference systems. The effects of the time datum interoperability and corresponding resolving strategies are also discussed. The influences of the interoperability problems of GNSS are summarized.

A Three-dimensional Water Vapor Tomography Algorithm Based on the Water Vapor Density Scale Factor

YAO Yibin, ZHAO Qingzhi, HE Yadong, LI Zufeng

2016, 45(3):  260-266.  doi:10.11947/j.AGCS.2015.20150205

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A water vapor tomography algorithm is proposed based on the water vapor density scale factor, which improves the utilization of observation. Real GPS and meteorological data from CORS network in Hong Kong were utilized to validate the proposed approach and analyze the influence under different weather conditions. Tomographic results of the proposed approach were compared with radiosonde data from 45004 station. The statistical result shows that the utilization of observation of the proposed approach is larger than that of traditional method, and the RMS, water vapor profile and error distribution are better than the traditional methods. In addition, the influence of tomographic result under the weather of precipitation is more severe than that of no precipitation weather.

Analytical Close-form Solutions for Three-dimensional Datum Transformation with Big Rotation Angles

LI Bofeng, HUANG Shanqi

2016, 45(3):  267-273.  doi:10.11947/j.AGCS.2016.20150108

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The small rotation angles are typically involved in the traditional geodetic datum transformation, for which one can iteratively solve for its linearized model with ignoring its second-smaller terms. However, the big rotation angles are introduced to transform the outcomes from the advanced space surveying techniques. For this transformation model with big rotation angles, all elements of rotation matrix are usually parameterized as unknown parameters and then solved with the constrained adjustment theory by using the orthogonal condition of rotation matrix. With three-dimensional datum transformation with big rotation angles as example, this paper derives the analytical close-form solutions by formularizing the coordinates of multi-points as a matrix and using the orthogonal condition of rotation matrix. Expanding the transformation model with introducing the errors to common points of both datum, we derive out its analytical solutions as well. The results of simulation computations show that the presented three-dimensional datum transformation can realize the comparable transformation result while the new method can outcome the complicated and time-consuming iterations, therefore improving the computation efficiency.

Analysis of Characteristics of QZSS Satellite Orbit and Clock Products during Yaw Attitude Model Switching

ZHOU Peiyuan, DU Lan, FANG Shanchuan, LU Yu, ZHANG Zhongkai, LI Fupeng

2016, 45(3):  274-281.  doi:10.11947/j.AGCS.2016.20150386

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Yaw attitude model switching of navigation satellites have great impact on its orbit and clock products derived from precise orbit determination. Firstly, the yaw attitude and solar radiation model of QZSS is given briefly. Then, using QZSS precise orbit and clock products provided by IGS MGEX analysis center, precision of orbit and clock is analyzed by satellite laser ranging residuals and polynomial fit residuals respectively. Finally, spectral analysis and modified Allan variance is carried out on clock products to reveal its periodic variations. Research on QZSS satellite orbit and clock products of 2014 shows that there are two eclipse seasons of 20 days and the beta angle is fluctuating with a period of half-year. And there is significant correlation between the precision of orbit and clock products and beta angle. Moreover, the satellite clock offset has periodic variations similar to orbit periods and its amplitude is changing with the beta angle which indicates problems of current orbit determination strategies. In view of similarities between QZSS and BeiDou IGSO and MEO satellites in yaw attitude model, the conclusion is beneficial to improve BeiDou precise orbit determination.

On-orbit Geometric Parameters Refinement of Mapping Satellite-1 Triple Line Array Camera

GENG Hongyi, GONG Zhihui, GAO Chao, YANG Jianfeng, TANG Ke

2016, 45(3):  282-290.  doi:10.11947/j.AGCS.2016.20150206

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To find the model and method of on-orbit geometric refinement suitable for the triple line array camera of Mapping Satellite-1, this paper first analyzed the impact of the exterior orientation line element error on the geometric parameters refinement, then eliminated the high-frequency noise by the preprocessing of the attitude data, and compensated the low-frequency flutter of satellite platform in the course of flying by sine function and designed the constant angular error model for the lens of the triple line array camera. In addition, an interior orientation model, using directly pixel coordinates as observations, was constructed based on conventional additional parameter model and the combination of the best refinement model parameters and the solution strategy were determined by the unilateral control extrapolative location. The experiments show that the planar accuracy and vertical accuracy are about 1 GSD and 0.8 GSD by the proposed refinement plan and the rational distribution of GCPS.

Mixed LS-TLS Estimation Based on Nonlinear Gauss-Helmert Model

FANG Xing, ZENG Wenxian, LIU Jingnan, YAO Yibin, WANG Yong

2016, 45(3):  291-296.  doi:10.11947/j.AGCS.2016.20150157

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For the case of design matrix in EIV(errors-in-variables) model containing both fixed elements and random elements, this paper proposes a mixed LS-TLS(least squares-total least squares) algorithm and deduces the precision estimator by reformulating an EIV model as a nonlinear Gauss-Helmert model, in which random elements are extracted to the random model of adjustment. This algorithm can be applied to the general design matrix including simultaneously fixed columns, fixed elements and random elements. The example illustrates that the solution of mixed LS-TLS equal the solution of structured or weighted TLS algorithms which can solve mixed LS-TLS problem. Additionally, the solution of mixed LS-TLS statistically superior to solution of LS or TLS.

Solution for Robust Total Least Squares Estimation Based on Median Method

TAO Yeqing, GAO Jingxiang, YAO Yifei

2016, 45(3):  297-301.  doi:10.11947/j.AGCS.2016.20150234

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Because the present algorithms of total least squares for robust estimation have disadvantages, solution for computation primary model parameters based on median method is proposed. And to get over the influence that estimation error of random model and error of mean square has, computation weight matrix of observation vector and coefficient matrix separately are proposed. Iterative algorithm of robust total least squares is established based on median method, and to prove the proposed solution to be feasible, an instance is cited. The numerical results of the instance clearly demonstrate that the presented solution is more accurate than the traditional method for line fitting.

Real Order and Logarithmic Moment Estimation Method of P-norm Distribution

PAN Xiong, LUO Jing, WANG Yao

2016, 45(3):  302-309.  doi:10.11947/j.AGCS.2016.20150166

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The estimation methods of P-norm distribution is improved in this paper from the perspective of the parameters estimation precision and algorithm complexity. The real order and logarithmic moment estimation is introduced and the real order moment estimation method of P-norm distribution is established based on the actual error distribution. First of all, the relation between the shape parameter p and the real order value r is derived by using the real order moment estimation, and corresponding suggestions are provided for shape parameter's selection. Then, the nonlinear estimation formula of shape parameter, expectations and mean square error is derived via logarithmic moment estimation, function truncation error on the calculation of parameter estimation is eliminated and the solving method of corresponding parameters and calculation process is given, leading an improvement of the theory. Finally, some examples are performed for analyzing the stability and precision of such three methods including real order moment, logarithmic moment and maximum likelihood estimation. The result shows that the stability, precision and convergence speed of the method in this paper are better than maximum likelihood estimation, which generalized the existing errors theory.

Automatic Tie-points Extraction for Triangulation of Large-scale Oblique Multi-view Images

YAN Li, FEI Liang, YE Zhiyun, XIA Wang

2016, 45(3):  310-317.  doi:10.11947/j.AGCS.2016.20140673

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A new tie-points extraction and bundle block adjustment method for large-scale multi-view oblique images is presented. Firstly, exterior orientation data gained by POS are used to rectify oblique images and predict image correspondences, which can be matched using SIFT algorithm. Secondly, an unordered feature tracking method relies on union-find algorithm are adapted to detect the multi-view correspondences. After tie-points extracted, bundle adjustment are done with POS and control points data treated as weighted measurement. In the experiment part, three kinds of oblique images, taken by assembled lightweight oblique system, UltraCam and SWDC-5, are used to test the algorithm above. The results show that our method can adapt the popular oblique systems at home and abroad, which can process over 2000 images at a time. And the precision of oblique triangulation is better than the traditional vertical triangulation, with an accuracy of 0.75 GSD in horizontal direction, 2.0 GSD in elevation direction.

Feature Matching for SAR and Optical Images Based on Gaussian-Gamma-shaped Edge Strength Map

CHEN Min, ZHU Qing, ZHU Jun, XU Zhu, HUANG Lanxin

2016, 45(3):  318-325.  doi:10.11947/j.AGCS.2016.20150084

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A matching method for SAR and optical images, robust to pixel noise and nonlinear grayscale differences, is presented. Firstly, a rough correction to eliminate rotation and scale change between images is performed. Secondly, features robust to speckle noise of SAR image are detected by improving the original phase congruency based method. Then, feature descriptors are constructed on the Gaussian-Gamma-shaped edge strength map according to the histogram of oriented gradient pattern. Finally, descriptor similarity and geometrical relationship are combined to constrain the matching processing.The experimental results demonstrate that the proposed method provides significant improvement in correct matches number and image registration accuracy compared with other traditional methods.

A SRTM-DEM-controlled Ortho-rectification Method for Optical Satellite Remote Sensing Stereo Images

ZHANG Hao, ZHANG Guo, JIANG Yonghua, WANG Taoyang

2016, 45(3):  326-331.  doi:10.11947/j.AGCS.2016.20150358

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In response to the problem of lacking of control base in the project of global mapping, a method to ortho-rectify satellite remote sensing images is proposed, which uses SRTM-DEM as control base. First, stereo images pairs which compose of optical images are adjusted by block adjustment of free networks and DEMs are extracted.Then SRTM-DEM is used as control base, the single DEM is the cell model and DEM block adjustment of independent models is implemented to get orientation parameters of each model.Finally, the geometric model parameters of each stereo image pair are corrected to ortho-rectify the nadir image. The ZY-3 images in Xianning and Jiangxi are taken as test data and the results show that the planar orientation accuracy of the pan nadir image is improved from 12.93 pixels to 6.85 pixels.

Fish-eye Camera Calibration Model Based on Vector Observations and Its Application

ZHAN Yinhu, ZHENG Yong, ZHANG Chao, LUO Yabo, WANG Kai

2016, 45(3):  332-338.  doi:10.11947/j.AGCS.2016.20150080

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A fish-eye camera calibration model is presented, basic observations of which consist of both half angle of view and azimuth. Rodrigues matrix is introduced into the model, and three Rodrigues parameters instead of Euler angles are used to represent elements of exterior orientation in order to simplify the expressions and calculations of observation equations.The new model is compared with the existing models based on half angle of view constraint by actual star-map data processing, and the results indicate that the model is superior to control the azimuth error, while slightly inferior to constrain the error of half angle of view. It is advised that radial distortion parameters should be determined by the model based on half angle of view constraint at first, and other camera parameters should be calculated by the new model.

SAR Images Unsupervised Change Detection Based on Combination of Texture Feature Vector with Maximum Entropy Principle

ZHUANG Huifu, DENG Kazhong, FAN Hongdong

2016, 45(3):  339-346.  doi:10.11947/j.AGCS.2016.20150022

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Generally, spatial-contextual information would be used in change detection because there is significant speckle noise in synthetic aperture radar(SAR) images. In this paper, using the rich texture information of SAR images, an unsupervised change detection approach to high-resolution SAR images based on texture feature vector and maximum entropy principle is proposed. The difference image is generated by using the 32-dimensional texture feature vector of gray-level co-occurrence matrix(GLCM). And the automatic threshold is obtained by maximum entropy principle. In this method, the appropriate window size to change detection is 11×11 according to the regression analysis of window size and precision index. The experimental results show that the proposed approach is better could both reduce the influence of speckle noise and improve the detection accuracy of high-resolution SAR image effectively; and it is better than Markov random field.

3D Power Line Reconstruction from Airborne LiDAR Point Cloud of Overhead Electric Power Transmission Corridors

LIN Xiangguo, ZHANG Jixian

2016, 45(3):  347-353.  doi:10.11947/j.AGCS.2016.20150186

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3D power line reconstruction is one of the main tasks in power line patrols using LiDAR systems mounted on helicopters. A 3D reconstruction method is proposed to reconstruct the power lines from the airborne LiDAR point clouds of the overhead electric power transmission corridors. Firstly, the pylons' LiDAR points and the initial routine trajectory of the transmission lines are employed to derive the precise information such as the locations and number of the pylons, the real routine trajectory, and the total number of spans. Secondly, the power line corridor is divided into a number of spans, the scope of each span in the XOY plane is determined, and the powerline LiDAR points are allocated into the corresponding spans where they are located. Thirdly, the powerline points of each span are clustered by the k-means algorithm in a normalized projection space, and each cluster corresponds to one power line. Finally, each power line is reconstructed based on a combination of a line model and a parabola model. Two experiments suggest that the proposed method is capable of automatically and correctly reconstructing 3D models of the long power lines with high accuracy. Moreover, it is robust to many factors such as the changing number, types, arrangements, blunders of the power lines, the changing length of the spans, and the irregular breakage of the LiDAR point clouds.

Avoiding Special Conflicts in Road Simplification by Using Road Bends

HE Haiwei, QIAN Haizhong, WANG Xiao, HU Huiming, CHEN Jingnan

2016, 45(3):  354-361.  doi:10.11947/j.AGCS.2016.20140576

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This paper proposed a method which aims to avoid the conflicts caused by the simplification of road networks by using road bends. First, using road bend as basic unit to analyze the morphological changes of the curve line, different types of the spatial conflicts in road simplification process were studied. Second, the identification rules of different types of conflicts were studied based on the special relations between road bends and other features. Finally, using the controllability of road bends and the indirect simplification by using bend groups, to avoid the conflicts. Comparing results illustrated that this method can effectively identify and avoid the special conflicts during the road simplification and maintaining the special relation consistency of the data.

A Quantitative Calculation Method of Composite Spatial Direction Similarity Concerning Scale Differences

CHEN Zhanlong, GONG Xi, WU Liang, AN Xiaoya

2016, 45(3):  362-371.  doi:10.11947/j.AGCS.2016.20150099

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This article introduces a new model for direction relations between multiple spatial objects at multiple scales and a corresponding similarity assessment method. The model is an improvement of direction relation matrix, which quantitatively models direction relations on object scale, and by the idea of decomposition and means of the optimum solution of the transportation problem to solve the minimum conversion cost between multiple direction matrices, namely distance between a pair of matrices, thus quantified the difference between a pair of directions, finally obtain the similarity values between arbitrary pairs of multiple spatial objects and compare the results. Experiments on calculating similarity between objects at different scales show that the presented method is efficient, accurate, and capable of obtaining results consistent with human cognition.

A Momentum Function Description and Tessellation Method for Polyline

WU Mingguang, ZHENG Peibei, LÜ Guonian

2016, 45(3):  372-378.  doi:10.11947/j.AGCS.2016.20140545

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Without taking polyline global structure into consideration, current polyline tessellation methods tend to make low quality decomposition. It makes them difficult to support vector mapping with large dataset and dynamic mapping with high update rate. This paper proposed a polyline momentum function and designed a monotone decomposition and tessellation method. The monotonous increasing intervals of the momentum function, as the gradient intervals of polyline, are divided continuously into optimized triangle strips. The monotone decreasing intervals of the momentum function, as the mutational intervals of polyline, are divided discretely into optimized triangle fans. The experiment results show that the decomposition quality measured by the numbers of triangulation vertices, triangles and primitives using this method are better than that based on vertex and line segment and can significantly improve the drawing efficiency for polyline. This method is also applicable to closed, width gradient and smooth line style.