Wuhan Institute of Surveying and Mapping

Wuhan, China

Wuhan Institute of Surveying and Mapping

Wuhan, China
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Jiang W.,Wuhan University | Xia C.,Wuhan University | Xia C.,Wuhan Institute of Surveying and Mapping | Li Z.,Wuhan University | And 2 more authors.
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2014

In order to discuss environmental loading effects on regional GPS coordinate time series, the data which includes Crustal Movement Observation Network of China (CMONOC) measurements from 1999 to 2011 and Wuhan Continuous Operational Satellite Positioning and Serving Syetem (WHCORS) measurements from 2007 to 2012, together with China and around 35 IGS stations measurements are reprocessed by GAMIT, and the GPS fiducial stations coordinate time series under the ITRF2008 are obtained. The effects of environmental loading are then calculated by QOCA to correct the coordinate time series. It is found that the displacements of GPS stations inside China caused by environmental loading exhibit remarkable regional characteristics. Coherent and bigger variations exist in the northeast, north and central China, as well as the southwest regions, among which the biggest root mean square (RMS) of the vertical loading displacement for stations in southwest region(KUNM) reaches up to 6.09 mm. By comparing the corrected and the uncorrected time series, it is found that environmental loading correction could remarkably reduce the non-linear variations of most stations' vertical and east coordinate time series inside China (accounting for about 70% of the selected GPS fiducial stations), among which the biggest reduction in the weighted root mean square (WRMS) reaches 1.5 mm. However, the improvement in the north components is quite limited. ©, 2014, SinoMaps Press. All right reserved.

Chen M.,Hubei Engineering University | Lu W.,Hubei Engineering University | Wan Y.,Hubei Engineering University | Tian S.,Wuhan Institute of Surveying and Mapping | Yang W.,Hubei Engineering University
Zhongguo Jiguang/Chinese Journal of Lasers | Year: 2016

An automatic point clouds registration method is proposed based on geometric information. This method can realize point cloud automatic registration without additional intensity and images information. Feature points of registration scans are extracted by feature distance histogram, and the initial matching sets of matching points are searched by K closet neighbor search in feature space. Relative height and the normal vector similarity measure are put forward, false match is eliminated combining with the root mean square distance and the initial conversion parameters are calculated. Points of low complexity are selected by Shannon entropy to participate in iterative closet point (ICP) accurate registration. Experimental results of real point cloud data show that, the proposed method can eliminate false matching of initial matching set, get better initial transform parameters, and improve the efficiency and precision of ICP algorithm. © 2016, Chinese Lasers Press. All right reserved.

Lu L.,Wuhan University | Lu L.,Collaborative Innovation Center for Geospatial Technology | Liu W.,Wuhan University | Liu W.,Collaborative Innovation Center for Geospatial Technology | Li J.,Wuhan Institute of Surveying and Mapping
Wuhan Daxue Xuebao (Xinxi Kexue Ban)/Geomatics and Information Science of Wuhan University | Year: 2016

The ambiguity resolution is one of the primary problems in GNSS carrier phase measurement. To acquire carrier phase integer ambiguity rapidly and accurately, we often take advantage of integer least-squares (ILS) estimation criterion to resolve ambiguity. Due to ILS problem can be regarded as closest vector problem (CLP) in lattice theory, therefore, lattice reduction could help to accelerate ambiguity enumeration process, shorten the search time, and further to improve the computation efficiency of ambiguity resolution. Among many of lattice reduction algorithms, Lenstra-Lenstra-Lovász (LLL) is a most popular and widely used reduction algorithm in many fields. It includes two reduction conditions, size reduction and basis vector swapping. However, size reduction is aimed at all matrix elements and basis vector swapping is only limited to two adjacent vectors, that will result in the unnecessary elements size reduction and excessive basis vector swapping times. Hence, both of them are not conducive to improving the ambiguity reduction efficiency, especially for high-dimensional ambiguity resolution. To overcome this problem, we adopt the greedy algorithm and partial column vector reduction to reduce the number of basis swapping and size reduction, in this contribution the computing complexity of LLL reduction algorithm is reduced, where LLL reduction algorithm has a long time-consuming under high-dimensional conditions. Simulations and real data validations have clearly shown that the modified LLL reduction algorithm can significantly improve the computational efficiency. Therefore our modified LLL algorithm has a certain useful value for fast resolution under high-dimensional case. © 2016, Research and Development Office of Wuhan University. All right reserved.

Lu L.,Wuhan University | Liu W.,Wuhan University | Li J.,Wuhan Institute of Surveying and Mapping
Cehui Xuebao/Acta Geodaetica et Cartographica Sinica | Year: 2015

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. ©, 2015, SinoMaps Press. All right reserved.

Hu Z.,Wuhan University | Liu Y.-R.,Wuhan University | Wu S.,Wuhan University | Wu S.,Wuhan Institute of Surveying and Mapping | And 2 more authors.
Yantu Lixue/Rock and Soil Mechanics | Year: 2014

Based on the sandstone's high geostress area from where a high slope in Jinping, a series of pre-peak unloading tests have been carried out; and the complete stress-strain curve, deformation characteristics and degradation effect of deformation parameters are studied. The test results show that compared to loading failure, the rock's brittle characteristics of unloading failure is obvious; and unloading failure needs lower deviatoric stress under the same initial confining pressure. The lateral strain and volumetric strain increase sharply in the process of unloading; and the expansion characteristics in the unloading direction is obvious. When the initial confining pressure is less than a value(30 MPa), the rock's failure unloading percentage would increase along with initial confining pressure's enlargement. But when initial confining pressure grow up to a value(40 MPa), the brittle characteristics is very obvious; and a few unloading percentage can cause the rock failure. Taking unloading percentage H which expresses unloading level as variable quantity, and making fitting of deformation parameters when in high and low stress. We get the functions between deformation degradation parameters and unloading percentage under unloading process. The test results and calculation method could benefit excavation for the stability analysis of slope under high geostress.

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