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    20 May 2015, Volume 44 Issue 5
    Impact on Nonlinear Vertical Variation of GNSS Reference Stations Caused by Thermal Expansion
    JIANG Weiping, WANG Kaihua, DENG Liansheng, LI Zhao
    2015, 44(5):  473-480.  doi:10.11947/j.AGCS.2015.20140296
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    Thermal expansion of GPS monuments and nearby bedrock could result in vertical changes in the coordinate time series of GNSS reference stations. In this paper, an improved method was developed to compute the magnitude of vertical variations caused by thermal expansion. Firstly, we calculated the effect on GPS monument and bedrock caused by thermal expansion based on land surface temperature data of GNSS reference stations and thermal expansion model. Secondly, we estimated the circular frequencies, amplitudes and phases using the method of least squares fitting instead of the current method which estimated only the amplitudes and phases information. Finally, we studied the periodic characteristics of the vertical variations caused by our modified thermal expansion model. Through analyzing the results of 9 representative IGS stations, we concluded that thermal expansion of GPS monuments and nearby bedrock could result in vertical variations of GNSS stations. The maximum variations could reach up to 0.57 mm and 1.85 mm at these stations respectively. The vertical variation caused by thermal expansion exhibited both annual and semiannual characteristics, which could explain 11.2% and 3.3% of the total annual and semi-annual variations in the up component of the coordinate time series respectively, and the magnitudes became larger with the increasing of their latitudes. Meanwhile, the amplitudes of the annual variations were much larger than that of the semi-annual variations. Meanwhile, some other small period (about 51 days) was also detected at some of these stations. In addition, we chose 107 IGS reference stations and computed the annual amplitudes and phases caused by thermal expansion of all these stations based on the method aforesaid. The results show that the maximum annual amplitude can reach to 3.3 mm, and their magnitudes show positive correlation with their latitudes prominently.

    Impact of Decorrelation on Search Efficiency of Ambiguity Resolution
    LU Liguo, LIU Wanke, LI Jiangwei
    2015, 44(5):  481-487.  doi:10.11947/j.AGCS.2015.20140311
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    The decorrelation performance of LAMBDA algorithm, LLL algorithm and Seysen algorithm are analyzed with evaluation indexes, i.e., condition number, orthogonal defect and S(A). Moreover, relationships between decorrelation performance of the above algorithms and ambiguity search efficiency are evaluated using theoretical and practical validation, respectively. The results validate that there is no inevitable relation between decorrelation performance of variance-covariance matrix of original ambiguity and search efficiency, whereas, traditional views consider that search efficiency can be enhanced just by improving decorrelation performance. Further analysis shows that the essence to improving search efficiency major depends on the permutation of basis vectors according to a certain direction.

    A Fast and High-precision Orientation Algorithm for BeiDou Based on Dimensionality Reduction
    ZHAO Jiaojiao, QU Jianghua, YUAN Hong
    2015, 44(5):  488-494.  doi:10.11947/j.AGCS.2015.20140055
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    A fast and high-precision orientation algorithm for BeiDou is proposed by deeply analyzing the constellation characteristics of BeiDou and GEO satellites features.With the advantage of good east-west geometry, the baseline vector candidate values were solved by the GEO satellites observations combined with the dimensionality reduction theory at first.Then, we use the ambiguity function to judge the values in order to obtain the optical baseline vector and get the wide lane integer ambiguities. On this basis, the B1 ambiguities were solved. Finally, the high-precision orientation was estimated by the determinating B1 ambiguities. This new algorithm not only can improve the ill-condition of traditional algorithm, but also can reduce the ambiguity search region to a great extent, thus calculating the integer ambiguities in a single-epoch.The algorithm is simulated by the actual BeiDou ephemeris and the result shows that the method is efficient and fast for orientation. It is capable of very high single-epoch success rate(99.31%) and accurate attitude angle (the standard deviation of pitch and heading is respectively 0.07°and 0.13°)in a real time and dynamic environment.
    Parallel Robust Estimation for Large-scale High-precision GNSS Baseline Vector Network
    CUI Yang, LÜ Zhiping, ZHANG Youyang, LI Linyang
    2015, 44(5):  495-502.  doi:10.11947/j.AGCS.2015.20140154
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    According to the characteristics of large-scale GNSS baseline vector network, the relevant observations robust estimation model which is based on RECO scheme is improved by parallel computing. A feasible process steps are also presented. Using the improved model, a numerical example is given. It is demonstrated that the large-scale GNSS baseline vector related robust parallel estimation not only can inhibit the influence of the outliers to the parameter estimates, but also significantly improve the computational efficiency.

    Aerial Triangulation Close-range Images with Dual Quaternion
    SHENG Qinghong, LIU Jianfeng, YU Mengxin, WANG Huinan
    2015, 44(5):  503-509.  doi:10.11947/j.AGCS.2015.20130533
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    A new method for the aerial triangulation of close-range images based on dual quaternion is presented. Using dual quaternion to represent the spiral screw motion of the beam in the space, the real part of dual quaternion represents the angular elements of all the beams in the close-range area networks, the real part and the dual part of dual quaternion represents the line elements corporately. Finally, an aerial triangulation adjustment model based on dual quaternion is established, and the elements of interior orientation and exterior orientation and the object coordinates of the ground points are calculated. Real images and large attitude angle simulated images are selected to run the experiments of aerial triangulation. The experimental results show that the new method for the aerial triangulation of close-range images based on dual quaternion can obtain higher accuracy.
    Doppler Centroid Estimation for Airborne SAR Supported by POS and DEM
    CHENG Chunquan, HUANG Guoman, YANG Jie
    2015, 44(5):  510-517.  doi:10.11947/j.AGCS.2015.20140135
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    It is difficult to estimate the Doppler frequency and modulating rate for airborne SAR by using traditional vector method due to instable flight and complex terrain. In this paper, it is qualitatively analyzed that the impacts of POS, DEM and their errors on airborne SAR Doppler parameters. Then an innovative vector method is presented based on the range-coplanarity equation to estimate the Doppler centroid taking the POS and DEM as auxiliary data. The effectiveness of the proposed method is validated and analyzed via the simulation experiments. The theoretical analysis and experimental results show that the method can be used to estimate the Doppler centroid with high accuracy even in the cases of high relief, instable flight, and large squint SAR.
    Automatic Registration of Low Altitude UAV Sequent Images and Laser Point Clouds
    CHEN Chi, YANG Bisheng, PENG Xiangyang
    2015, 44(5):  518-525.  doi:10.11947/j.AGCS.2015.20130558
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    It is proposed that a novel registration method for automatic co-registration of unmanned aerial vehicle (UAV) images sequence and laser point clouds. Firstly, contours of building roofs are extracted from the images sequence and laser point clouds using marked point process and local salient region detection, respectively. The contours from each data are matched via back-project proximity. Secondly, the exterior orientations of the images are recovered using a linear solver based on the contours corner pairs followed by a co-planar optimization which is implicated by the matched lines form contours pairs. Finally, the exterior orientation parameters of images are further optimized by matching 3D points generated from images sequence and laser point clouds using an iterative near the point (ICP) algorithm with relative movement threshold constraint. Experiments are undertaken to check the validity and effectiveness of the proposed method. The results show that the proposed method achieves high-precision co-registration of low-altitude UAV image sequence and laser points cloud robustly. The accuracy of the co-produced DOMs meets 1:500 scale standards.

    Optimization Approach for Multi-scale Segmentation of Remotely Sensed Imagery under k-means Clustering Guidance
    WANG Huixian, JIN Huijia, WANG Jiaolong, JIANG Wanshou
    2015, 44(5):  526-532.  doi:10.11947/j.AGCS.2015.20130497
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    In order to adapt different scale land cover segmentation, an optimized approach under the guidance of k-means clustering for multi-scale segmentation is proposed. At first, small scale segmentation and k-means clustering are used to process the original images; then the result of k-means clustering is used to guide objects merging procedure, in which Otsu threshold method is used to automatically select the impact factor of k-means clustering; finally we obtain the segmentation results which are applicable to different scale objects. FNEA method is taken for an example and segmentation experiments are done using a simulated image and a real remote sensing image from GeoEye-1 satellite, qualitative and quantitative evaluation demonstrates that the proposed method can obtain high quality segmentation results.

    Multi-temporal and Dual-polarization Interferometric SAR for Land Cover Type Classification
    WANG Xinshuang, CHEN Erxue, LI Zengyuan, YAO Wanqiang, ZHAO Lei
    2015, 44(5):  533-540.  doi:10.11947/j.AGCS.2015.20130244
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    In order to study SAR land cover classification method, this paper uses the multi-dimensional combination of temporal,polarization and InSAR data. The area covered by space borne data of ALOS PALSAR in Xunke County,Heilongjiang Province was chosen as test site. A land cover classification technique of SVM based on multi-temporal, multi-polarization and InSAR data had been proposed, using the sensitivity to land cover type of multi-temporal, multi-polarization SAR data and InSAR measurements, and combing time series characteristic of backscatter coefficient and correlation coefficient to identify ground objects. The results showed the problem of confusion between forest land and urban construction land can be nicely solved, using the correlation coefficient between HH and HV, and also combing the selected temporal, polarization and InSAR characteristics. The land cover classification result with higher accuracy is gotten using the classification algorithm proposed in this paper.

    Mural Image Rectification Based on Correction of Laser Point Cloud Intensity
    FANG Wei, HUANG Xianfeng, ZHANG Fan, LI Deren
    2015, 44(5):  541-547.  doi:10.11947/j.AGCS.2015.20140244
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    Image rectification can reduce the distortion of digital mural image and attach rectified image with spatial properties, thus becomes one of key steps in mural image digital protection. As an intermediate data of 2D and 3D, intensity information of laser scanning is significant on texture mapping and rectification of mural images in grottos. However, the unusual phenomenon of laser intensity at near distance makes it very difficult on extracting feature points for image rectification needed. To eliminate the near distance effect on intensity-based mural rectification, the procedure of laser transmission was studied and the intensity function of defocusing effect of laser receiving optics was deduced. By dividing point cloud intensity values with corresponding values of functions with estimated parameters from collected sample data, range and incidence angle invariant relative reflectance was generated, thus unusual intensity of point cloud data was corrected effectively. Experiments demonstrate that this method can effectively solve the problem of feature points in respect of low density and uneven distribution, thus achieve better results than general digital image processing method.

    Research of Two-media Underwater Reefs Depth Measurement Experiment Based on Low-altitude UAV
    ZHOU Gaowei, LI Yingcheng, REN Yanxü, SHENG Lin, YE Dongmei, FAN Fengyun, BAI Jie
    2015, 44(5):  548-554.  doi:10.11947/j.AGCS.2015.20140259
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    Based on the principle of two-media photogrammetry and with islands UAV images, a test of two-media photogrammetry is carried out. Firstly, there is an introduction of the principle of two-media photogrammetry. In the following step, the two-media photogrammetry requirements on the accuracy of the refractive index of sea water is discussed. Then, a new method for calculating the elevation correction coefficient is developed. The test procedure of two-media underwater reefs depth measurement based on low-altitude UAV images of underwater reefs surrounding the islands is designed. The test shows that aerial two-media photogrammetry is feasible in practical application, but relatively high requirements for aerial photography conditions.
    Hierarchical Semantic Model of Geovideo
    XIE Xiao, ZHU Qing, ZHANG Yeting, ZHOU Yan, XU Weiping, WU Chen
    2015, 44(5):  555-562.  doi:10.11947/j.AGCS.2015.20140176
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    The public security incidents were getting increasingly challenging with regard to their new features, including multi-scale mobility, multistage dynamic evolution, as well as spatiotemporal concurrency and uncertainty in the complex urban environment. However, the existing video models, which were used/designed for independent archive or local analysis of surveillance video, have seriously inhibited emergency response to the urgent requirements.Aiming at the explicit representation of change mechanism in video, the paper proposed a novel hierarchical geovideo semantic model using UML. This model was characterized by the hierarchical representation of both data structure and semantics based on the change-oriented three domains (feature domain, process domain and event domain) instead of overall semantic description of video streaming; combining both geographical semantics and video content semantics, in support of global semantic association between multiple geovideo data. The public security incidents by video surveillance are inspected as an example to illustrate the validity of this model.

    Handling Graphic Conflicts between Cartographic Features: Exemplifying Geo-linear Features(Road, River and Boundary)
    LI Lin, YU Zhonghai, ZHU Haihong, KUAI Xi
    2015, 44(5):  563-569.  doi:10.11947/j.AGCS.2015.20140129
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    According to the requirements of map quality by cartographic specifications, the current computer cartographic methodology and technology could not inevitably avoid manually intervening in resolving a large amount of graphic conflicts after symbolization. It results from the differences between Digital Landscape Models and Digital Cartographic Models and has been a bottleneck for fast map-making. Through an investigation into the appearance of cartographic conflicts and cartographic specifications, this article presents a set of basic operations to implement the cartographic strategy “processing before symbolizing” for handling graphic conflicts specifically on two forms of conflicts: graphic overlap and graphic connection. That strategy translates handling graphic conflicts caused by symbolization of geographic features into processing the features-selves so that a lot of thereby conflicts are removed. Applications of those basic operations in resolving cartographic conflicts are outlined by exemplifying some typical conflicts caused by the main topographic features: Road, River system and Boundary. Two experiments on producing topographic maps verify the applicability of the presented operations as well as the paradigm in this study in improving efficiency of map-making.

    An Efficient Trajectory Data Index Integrating R-tree, Hash and B*-tree
    GONG Jun, KE Shengnan, ZHU Qing, ZHANG Yeting
    2015, 44(5):  570-577.  doi:10.11947/j.AGCS.2015.20130520
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    To take into account all of efficiency and query capability, this paper presents a new trajectory data index named HBSTR-tree. In HBSTR-tree, trajectory sample points are collectively stored into trajectory nodes sequentially. Hash table is adopted to index the most recent trajectory nodes of mobile targets, and trajectory nodes will not be inserted into spatio-temporal R-tree until full, which can enhance generation performance in this way. Meantime, one-dimensional index of trajectory nodes in the form of B*-tree is built. Therefore, HBSTR-tree can satisfy both spatio-temporal query and target trajectory query. In order to improve search efficiency, a new criterion for spatio-temporal R-tree and one new node-selection sub-algorithm are put forward, which further optimize insertion algorithm of spatio-temporal R-tree. Furthermore, a database storage scheme for spatio-temporal R-tree is also brought up. Experimental results prove that HBSTR-tree outperforms current methods in several aspects such as generation efficiency, query performance and supported query types, and then supports real-time updates and efficient accesses of huge trajectory database.
    Version Similarity-based Model for Volunteers' Reputation of Volunteered Geographic Information: A Case Study of Polygon
    ZHAO Yijiang, ZHOU Xiaoguang
    2015, 44(5):  578-584.  doi:10.11947/j.AGCS.2015.20140065
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    At present, it is difficult to evaluate the quality of volunteered geographic information(VGI), which have malicious, false, and poor quality data. Therefore, a version similarity-based reputation model for volunteers of VGI system is proposed. In the model, each editing to a geographic spatial object of each volunteer is defined as a version. When the object version is modified by other users, support degree of the version is computed through version similarity. Then, support degree of every object contributed by a volunteer is calculated according by others' modifications. The volunteer's reputation is obtained through weighted average of all his support degrees. The version similarity composites major factors of spatial similarity and attributes similarity between versions of a same object. Polygon objects are employed as an example to describe the computation process of volunteer reputation of our model. For verifying and analyzing the rationality of our reputation model, Berlin's historical data from OpenStreetMap are used for experiments. It shows that users' reputation calculated by our model has a positive correlation with quality of objects contributed by them as a whole.

    Some Key Technologies of Geospatial Information System for China Water Census
    CAI Yang, XIE Wenjun, FU Jing, CHENG Yilian, CHEN Zidan, CHENG Jianguo
    2015, 44(5):  585-589.  doi:10.11947/j.AGCS.2015.20140476
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    We have pioneered research on geospatial information system for national water census and its application. Aiming to the main issues such as information obtaining, data management, quality control, and project organization, the overall thought is given. It is based on taking fundamental data as supporting and data model as precursor, and viewing intelligent tool as protective role, and combing the management theory with technical methods. The key techniques developed include the digital basin extraction, data modeling orienting to the object of water resources, data acquisition and processing within certain rules and the application of multidimensional theme.
    Interpretation of Event Spatio-temporal and Attribute Information in Chinese Text
    ZHANG Chunju
    2015, 44(5):  590-590.  doi:10.11947/j.AGCS.2015.20140657
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