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    Some notes on uncertainty, uncertainty measure and accuracy in satellite navigation
    Yuanxi Yang
    Acta Geodaetica et Cartographica Sinica   
    Abstract1529)   HTML    PDF(pc) (933KB)(2181)       Save
    Uncertainty always exists in satellite navigation process and results, which includes random errors, systematic errors, outliers and colored noises etc. There are many different measures for evaluating the quality of the navigation results, such as precision, accuracy, reliability and uncertainty, and so on. In practice, the accuracy, precision and error itself are often confused by the users, so are the uncertainty and the uncertainty measures. Especially, the accuracy is often followed several times standard deviation or error percentage. For example, the user range accuracy (URA) index is often followed standard deviation. In this paper, the user range error (URE) is redefined based on the uncertainty concept. Then the URE and URA are distinguished and their relationship is obtained. The uncertainty is distinguished from the uncertainty measure. The often used reliability concept in geodetic adjustment is introduced and described. At last, several notes on the concept of error, precision, accuracy, URE and URA are given.
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    Cited: Baidu(40)
    Multipurpose Watermarking Algorithm for Digital Raster Map Based on Wavelet Transformation
    Acta Geodaetica et Cartographica Sinica   
    Abstract1252)   HTML    PDF(pc) (1343KB)(2215)       Save
    A compound watermarking algorithm for digital raster map is proposed based on wavelet transformation in this paper. The basic idea is to embed the robust watermark and the fragile watermark into different frequency blocks of the digital raster map based on the features of digital raster map with higher luminance and greater sensual capability than image data. The robust watermark is adaptively embedded into low frequency section to protect the copyright of the data. The fragile watermark is embedded into high frequency section by the dithered modulation technique to achieve the goal of content authentication according to the characteristics of human visual systems. The experiments show that the proposed algorithm can attest content integrity for digital raster map, and is robust against various malicious attacks such as JPEG compression, sharpening, cutting etc.
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    Cited: Baidu(23)
    Virtual Observation Method to Ill-posed Total Least Squares Problem
    Acta Geodaetica et Cartographica Sinica    2014, 43 (6): 575-581.  
    Abstract924)   HTML    PDF(pc) (1001KB)(1501)       Save
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    Cited: Baidu(19)
    Research on the High Accuracy Band-to-Band Registration Method of ZY-3 Multispectral image
    Acta Geodaetica et Cartographica Sinica    2013, 42 (6): 884-0.  
    Abstract850)   HTML    PDF(pc) (2081KB)(1649)       Save

    The ZiYuan-3 (ZY-3) surveying satellite is the first high-resolution civilian stereo mapping satellite of China, which carries one multispectral sensor with a spatial resolution of 5.8m. Fully considering the characteristic of the ZY-3 multispectral camera that all CCD chips of four bands scan through the same field, a novel method is proposed in this paper to achieve seamless multispectral images and high accuracy band-to-band registration by re-imaging with virtual CCD. In the experiment, the ZY-3 multispectral camera is calibrated with the ZY-3 images over Henan area and Tianjin area, meanwhile the correctness of the calibration results is validated by 30 high accuracy GCPs in the ZY-3 multispectral image over Hebei. Further, re-imaging method is applied to the ZY-3 images over Hebei area and Lanzhou area with the virtual CCD calculated from the calibrated interior orientation. Finally, the band-to-band registration is estimated by comparing image coordinates of the same points in different bands. The validity of the proposed method is proved by experimental result which indicates the band-to-band registration accuracy is better than 0.2 pixels.

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    Cited: Baidu(13)
    Adaptive Water Level Correction Algorithm for Flooding Analysis
    Acta Geodaetica et Cartographica Sinica    2013, 42 (4): 0-0.  
    Abstract429)      PDF(pc) (11473KB)(1362)       Save
    Flood loss assessment is the basis of flood control and disaster mitigation decision-making, and the primary tasks in flood assessment are to pinpoint the flooding area, depth of water and duration of flooding based on Digital Elevation Model (DEM). The limited resolution and random error of DEM result in abnormal depressions which embarrass the computation of flow direction. Traditional methods process the depressions in DEM by filling the depressions with the same elevation to create a depression-free surface, which result in new problems like the up-lifting of water level on slopes and flood cut-off in flat area. To overcome these shortcomings, this paper presents an adaptive water level correction algorithm for accurate flooding analysis to derive flooding area, flood depth and duration time. According to the characteristics of floods, the correction value is adaptive to flood rate, flood depth variation and flooding time. Terrains of different types range from flat to hilly to mountainous are selected for testing. Experimental results prove that by means of this method, more accurate and reliable flooding information can be available, which is prior to scientific and prompt flood assessment and decision-making.
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    Cited: Baidu(12)
    The Principles and Methods of Discrete Global Grid Systems for Geospatial Information Subdivision Organization
    Acta Geodaetica et Cartographica Sinica   
    Abstract814)      PDF(pc) (742KB)(1689)       Save
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    Cited: Baidu(11)
    Modeling and metrics of higher order fuzzy geographical phenomena
    Acta Geodaetica et Cartographica Sinica   
    Abstract1089)   HTML    PDF(pc) (2238KB)(1269)       Save
    Modeling and metrics of fuzzy geographical phenomena have gained some products. But existing models can’t measure the error of membership value, so those models can’t satisfy to objectively describe complex natural and artificial phenomena. The scale effect and measurement error are two major objective reasons which bring forth the membership error of vague geographical phenomena while subjectivity of relative workers and difference of standards between departments are major subjective reasons. A fuzzy geographical object model is proposed based on interval type-2 fuzzy sets, and the metrics of length of interval type-2 fuzzy line and area of interval type-2 fuzzy region are developed too, then the membership error of interval type-2 fuzzy geographical object is analyzed. This model can handle uncertainty of membership value and avoid some limitations of existing models. The model and relative metrics methods have broad applications in natural hazard analysis, global change , land cover change and so on.
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    Cited: Baidu(9)
    Estimation Model and Accuracy Analysis of BeiDou/GPS Real-time Precise Satellite Clock Error Integrated Resolving
    CHEN Liang, GENG Changjiang, ZHOU Quan
    Acta Geodaetica et Cartographica Sinica    2016, 45 (9): 1028-1034.   DOI: 10.11947/j.AGCS.2016.20150296
    Abstract1611)   HTML    PDF(pc) (1426KB)(2269)       Save
    Real-time high-precise satellite orbit and clock products are needed in real-time GNSS precise point positioning (PPP). In this paper, Estimation model and strategy of multi-GNSS precise satellite clock integrated resolving are researched and BeiDou/GPS real-time precise clock integrated estimation algorithm is realized by filter. Real-time simulation test results show: the STD accuracy of BeiDou/GPS real-time clock estimated in this paper compared to GFZ multi-GNSS precise clock(GBM) is about 0.15ns; horizontal accuracy after convergence of GPS kinematic PPP using simulation real-time clock products estimated in this paper is better than 5cm and vertical accuracy is better than 10cm, respectively; in BeiDou kinematic PPP test, horizontal and vertical accuracy results are same as the results using GFZ multi-GNSS precise clock(GBM) products, and the decimeter positioning can be realized.
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    Cited: Baidu(7)
    PS-InSAR Deformation Monitoring Data Processing Based on Multi-reference Points
    Acta Geodaetica et Cartographica Sinica   
    A Multi-constraints Displacement Method for Solving Spatial Conflict between Contours and Rivers
    LI Guohui XU Wenshuai LONG Yi ZHOU Tong GAO Chao
    Acta Geodaetica et Cartographica Sinica    2014, 43 (11): 1204-1210.   DOI: 10.13485/j.cnki.11-2089.2014.0189
    Abstract778)   HTML    PDF(pc) (1673KB)(1231)       Save

    In the process of spatial data integration and matching, the inconsistency often occurs between the rivers and contour lines that generate some spatial conflicts just like “river climbing slope”. Aiming to solve the problem by displacing the contours to matching the river network, this paper put forward a new method for every feature point on contour lines to establish specially its displacement model by affine transformation. The method comprehensively considered relative positions of adjacent ridge and valley points, the angle proportion of different feature points for displacing and local shape of contours to be maintained and transformed, so that the calculation of three constrained parameters determine the displacement of points on the contours that is angle, location and scaling was proposed. To test the method, several experiments were taken to analysis. The results showed that the research can effectively complete the displacement of contour lines to match the river network.

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    Cited: Baidu(3)
    Satellite Video Point-target Tracking in Combination with Motion Smoothness Constraint and Grayscale Feature
    WU Jiaqi, ZHANG Guo, WANG Taoyang, JIANG Yonghua
    Acta Geodaetica et Cartographica Sinica    2017, 46 (9): 1135-1146.   DOI: 10.11947/j.AGCS.2017.20160599
    Abstract972)   HTML    PDF(pc) (2831KB)(1302)       Save
    In view of the problem of satellite video point-target tracking, a method of Bayesian classification for tracking with the constraint of motion smoothness is proposed, which named Bayesian MoST. The idea of naive Bayesian classification without relying on any prior probability of target is introduced. Under the constraint of motion smoothness, the gray level similarity feature is used to describe the likelihood of the target. And then, the simplified conditional probability correction model of classifier is created according to the independence assumption Bayes theorem. Afterwards, the tracking target position can be determined by estimating the target posterior probability on the basis of the model. Meanwhile, the Kalman filter, an assistance and optimization method, is used to enhance the robustness of tracking processing. The theoretical method proposed are validated in a number of six experiments using SkySat and JL1H video, each has two segments. The experiment results show that the BMoST method proposed have good performance, the tracking precision is about 90% and tracking trajectory is smoothing. The method could satisfy the needs of the following advanced treatment in satellite video.
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    Cited: Baidu(2)