2010 Vol. 35, No. 4
Volunteered Geographic Information(VGI) is a new concept emerging with the development of geographic information science.This paper briefly analyses the sources,categories and characteristics of VGI data,presents the requirement of VGI data management,discusses the issues of data cleaning and quality control,focuses on the research of the VGI data management whose target is high performance processing of plotting queries and data updates.Two kinds of spatial data structures are presented.Dynamic binary line generalization tree,which is an extension to binary line generalization tree(BLG-tree),is designed to process the queries and updates of a single spatial object.Zoom quadtree,which includes two quadtree that function as spatial indexes and materialized views,is designed to index and organize the voluminous spatial objects.
Aiming at the automatic service composition of remotely sensed information processing service,this paper proposes a semantic matching based composition method.Based on remote sensing information ontology,a hierarchical semantic matching methods on both service category and remotely sensed image metadata is introduced.And a progressive composition is implemented by two steps:① the service and/or graph related to user requirement is created on-line to limit the services' selection range;② AO* based heuristic search algorithm is used for optimal path in the and/or graph.Typical remote sensing change detection application is employed as a case study.
Uncertain spatial relations are fundamental to querying and handling uncertain spatial data.However,there is a lack of models and approaches about uncertain relations to satisfy the requirements of many applications.In this study,the regions with broad boundaries are adopted first to model multi-source uncertain spatial data,and then the topology and direction between crisp regions are combined to represent the topological and direction relations related to uncertain regions.Finally,a method is presented to derive the symbolic directions concerned with uncertain regions from the corresponding symbolic description of topological relations according to the underlying knowledge between topology and direction.The derivation is a helpful complementary to current reasoning methods,and can be used to check inconsistencies of spatial data,handle spatial data query languages,and evaluate the similarity of spatial data.
Instantaneous traffic information can be collected by the Floating Car Data(FCD) method.Based on the establishment of "Shenzhen Urban Transportation Simulation System"(SUTSS),the paper explored how to use taxis as the data collection sensors in Shenzhen.Due to the nature of FCD,continuous GPS data such as routing velocities and coordinates can be collected by any GPS equipped vehicle.Therefore,relevant algorithms are developed and utilized for the map-matching according to probability and statistical theories.Furthermore,road segment velocity matching methods based on the Metropolis criteria is extended and relevant validation is carried out through the comparison of estimated and measured results.The major objective of this method is to obtain more accurate road segment travel time through the combination those estimated by FCD and historical ones.This can significantly improve the reliability of instantaneous traffic information before its web publication.Finally,this paper introduces the architecture and the realization of a web Geographical Information System(GIS) and FCD-based instantaneous traffic information dissemination system for the whole of Shenzhen City.
Spatial selectivity is significant to improve the accuracy of spatial query cost estimation.This paper proposes an accurate spatial selectivity estimation method based on Cumulative Density(CD) Histogram,which can deal with any arbitrary spatial query window.The method firstly estimates the histogram values of four corners of the spatial query window in Hll,Hlr,Hul,Hur histogram(recorded as S1,S2,S3,S4 respectively),and then the selectivity estimation of the spatial query is S1-S2-S3+S4.For estimate the value of any point in the histogram,the paper firstly ravels these grids which can affect estimation value of point(x,y) in histogram according to the principle of CD Histogram.We directly use these values of grids with certain values.To these grids without certain values,we amend it through the information provided by CD Histogram.These will make the amending more accurately,and improve the accuracy of selectivity estimation.This method can accurately estimate the query selectivity at arbitrary spatial query windows without add any additional assumption and storage disk,which can apply to a variety of vector data types,such as discrete,continuous distribution geographic data type,etc.
This paper presents a gird aided method for determining the convex hull of large amount data,the total time complexity of algorithm can achieve about O(n).The basic idea of the method is as follows.First,build a gird field which can cover with all planar points;then,figure out the position of every point in the gird field(such as the row and column place in the field).Afterwards,reserve the points which are in the gird field of leftmost(or rightmost) column or top(or bottom) row.Finally,execute Graham's algorithm to generate the convex hull with reserved points.The result of the tests indicates that there has some relationship between grid parameters and algorithm efficiency.Such as,with the increase in row-column number,the computational efficiency first rapid increase,followed by a gradual decrease.Additionally,when the row-column number select the evolution of total planar points' number,the pretreatment effect of the algorithm almost reach maximum.Furthermore,with the increase of the number of planar points,the elimination efficiency of gird aided method improves.
The high-quality routing on an electronic navigational chart is significant to safe,economical navigation for ships.Aiming to greedy weakness existing in automatic routing methods,this paper proposes an automatic algorithm for routing of ships based on route binary tree.Based on the definition and construction of route binary tree,the algorithm utilizes "Store in Section" to store the information of route binary tree,decomposes the information through "The Depth Priority" combined with "Sounding out Searching",and chooses the shortest distance-route automatically from the feasible routes finally.The experimental result shows the proposed method can overcome the drawback of traditional automatic routing algorithms,and improve the optimization result.
In view of some relief symbols are difficult to build the modeling in 3D topographic map,we take cliff symbol as the example to propose a method to exact the edge lines of cliff based on TIN,set up an illumination model of cliff symbol according to the visual sensation rules under the different illumination conditions and research the mathematical expression of it,and introduce the automatic modeling flows of cliff symbol.The experiment proves that it is feasible.The study will be helpful to build the modeling of other similar relief symbols automatically.
This paper proposes an information theory model for progressive selection of streets.This model has two key components: ① information sources which represents the information of the street network.② channels which represents how to select the streets.A set of new quantitative measures is proposed for geometric information and topological information of street network.The geometric information considers the variation of length proportion occupied by the streets.The topological information considers variation of the connection relation of the streets in the street network.Channels for communication are built according to the idea of matching.The transition probability is the key issue.For geometric information channel,eliminated street matches to all the remaining streets.The transition probability can be calculated form the joint probability easily.For topological information channel,the connection relation matches to the connection relation still remained and to the connection relation disappeared after a street was eliminated.The non-connected relation matches to the non-connected relation before a street was eliminated.The map generalization meaning of the channels is explained.The experimental result shows that the eliminated streets are those of shorter and with lower degree.
3D geological modeling is the key to 3D geological simulation and visualization software system.This paper studies the theory and algorithm of BSP tree-based Vector Shear,and raises a method which uses Vector shear to quickly build complex geological modeling and visually displays the inner information of geological bodies.In the end,it takes the example of geological digital engineering and 3D stratum analysis,and draws a conclusion that the algorithm is efficient and practical.
Based on the references of existing standard of ground object classification and CityGML feature classes,the paper studied design method of RS thematic model,analysed representation mechanism of geometric-topology and semantic attribute information based on CityGML,the methold was validated through data of a small region.
Absolute orientation is one of the fundamental issues in Photogrammetry and Remote Sensing. It is also an important topic in computer vision and three-dimensional reconstruction. To overcome the problem of large rotation angles between model coordinates of images and the corresponding world coordinates in close range applications, a new method of absolute orientation which is suitable for large oblique angle image is proposed. Singular value decomposition of rotation matrix is used to obtain accurate initial values of the angular elements. Least squares adjustment with gross error detection is also performed to achieve precise results of absolute orientation. Experimental results show that the proposed algorithm is effective and has well potential in various absolute orientation applications.
A contour lines extraction method for 3D water body from LiDAR point clouds data is proposed in this paper.First,all points are divided into rough and equidistant grids whose number,average elevation and height standard deviation of every grid points will be calculated later.Then,confirm the grids belonged to specific water areas with strict conditions according to four characters of the point clouds in the waters: the low density,the similarity of elevation in all points,the weak echo intensity,water surface is lower than the surrounding land.Next,exclude sparse and discrete blocks through the connected domain by the character of larger water areas.Finally,re-organize point clouds data by fine-grid.Extract water areas with the seed filling method under more relaxed conditions starting from the grids belonged to the specific water areas.Experiments indicate that this method is feasible.
Directional brightness temperature(DBT) plays an important role in surface energy balance and urban climate.Determination of components' proportion is one of the key factors to accurate simulation of DBT.An overview of the main components' proportion determination methods used currently on urban surfaces was unfolded and some techniques utilized in row crops were expanded to adapt three-dimensional urban targets,achieving radiosity method,horizontal projection method,oblique projection method and center projection method.Comparison between those above-mentioned four components' proportion determination methods demonstrate that they simulate the spatial distribution of DBT perfectly when the zenith angle is small.The result also shows that it is feasible to compute the components' proportion through sketching and calculating on the photograph filmed by a digital camera located near the thermal infrared sensor(center projection method).However,the horizontal projection method is an exception,which has a low precision corresponding to DBT when the zenith angle increased or differences between components' temperature extended to a higher level.Finally,a comparative study was conducted on simulation accuracies and complexities of different methods and some specific recommendations were given for diverse needs.
A multi-objective genetic algorithm for AUV path planning based on Vector Chart Format electronic charts is presented in this paper.In this method,real-code of variable length is adopted,several factors concerned with path quality are evaluated through fitness functions,and genetic operators such as selection,crossover,mutation,repair,deletion,together with population replacement method are proposed.Domain knowledge is introduced during the initial population formation and genetic operator design,in order that the produced path intersects obstruction area as less as possible,therefore the algorithm converges more quickly in the case of large-scale path planning.Experiments show that this multi-objective genetic algorithm can effectively improve algorithm convergence rate and global optimization ability.
Extracting damaged buildings accurately and quickly through remote sensing has an important meaning to damage evaluation and relief after earthquake.A method,which based only on high spatial resolution optical remotely sensed image acquired after earthquake and fused textural features and morphological features,was proposed to extract damaged buildings automatically.Besides,the use and behaving of different scales textural features and morphological features in damaged buildings extraction were investigated.A study case,Wenchuan Earthquake,was studied.Experiment results showed that this method could extract damaged buildings effectively and reach a good result that the product accuracy and the user accuracy of damaged buildings,and Kappa coefficient were 86.65%,86.35% and 0.790 6 respectively.
It is one of the important ways for GIS data updating based on map generalization.The critical first step in this way is to identify the correspondences between maps with the same area and to detect the updates.Matching roads for this purpose is studied in this paper.For matching of objects between roads,three matching levels,i.e.the decomposed level,basic level and abstracted level are discovered.Based on the order relationship of this three matching levels,matching of objects are accomplished by a set of algorithms developed.The results of the experiment for matching roads at scale 1∶10 000 and 1∶50 000 show that this method can obtain higher correct rate and meet requirement of updating.
The achievement and new progress in joint inversion of geodetic and seismological data for seismic source rupture process in the recent decade are summarized in this paper.The models,algorithms and typical earthquake cases in joint inversion of geodetic and seismological data for seismic source rupture process are discussed.The establishment of joint inversion model with GPS,InSAR and seismological data considering prior information and with inequality constraints is discussed.The functions of various data,determination of relative weight ratio and application of global optimization algorithm are emphatically discussed.
This paper investigated the seismic hazard assessment for the Yangon and its surrounding areas using the probabilistic approach.The seismic sources are defined spatially in nine source zones,characterized by a commonly used recurrence law and a maximum magnitude value.The present study area is situated between the latitudes of N 13°37′ and N 20°2′ and the longitudes of E 93°35′ and E 99°5′.The study areas of nine source zones are centered at Yangon with the radius about 200 km.The seismic hazard maps for Yangon and its surrounding areas including the peak ground acceleration values for 2% and 10% exceedance in 50 years were provided in this study.
In order to improve the precision of the altimetry gravity computed by the inverse Stokes formula,the geoidal height of the innermost area is expressed as double cubic polynomial,and a formula to calculate gravity anomaly of this area is derived after the non-singular transformation is introduced.The analysis based on the theoretical model of the geoidal height shows that the accuracy of this formula is quite high.A practical calculation is done based on the geoidal height data with a resolution of 2′×2′,and the results indicate that the contribution of the innermost area to the gravity anomaly recover should not be ignored.The formula derived in this paper could provide theoretical basis for the gravity anomaly recovery with high precision.
A novel multisensor multitarget unscented filter algorithm based on data compression,SD-DCUKF,is proposed for the centralized multsisensor multitarget tracking problem of nonlinear system in clutter.In the new algorithm,the measurements from multiple sensors are first combined according to the rule of generalized S-D assignment algorithm and the optimal partition can be achieved.In order to reduce the computation burden,a new coarse association rule is proposed for S-D assignment.Then in the optimal partition,the measurements from the same target are dealt with by use of the method of data compression.Based on these,UKF is used for the propagation of state distribution in nonlinear system and the SD-DCUKF algorithm is derived.According to the simulation results,the accuracy and robustness of proposed algorithm are improved compared with the MSJPDA/EKF algorithm.Furthermore,the method of coarse association proposed makes the computation time decrease by 62 percent.
Shepard method is applied in many science fields. Based on the basic principles of Shepard model, the structure of the cost function and the selection of the scattered data are improved in this article. The smoothness and decay capacity of the improved cost function is better and can be adjusted freely depending on the demand. As a result, the interpolation accuracy is increased and the implement of the improved method is more convenient in application. In the end, the experiments are made on the real gravity field data, the several statistical characteristics of the error is improved using the modified Shpard method in this article, which indicated our work is successful.
The GPS signal multipath effects is considered as a major error sources for the high-precision real-time dynamic deformation monitoring.The trend being extracted from the three-dimensional coordinate series are multipath model by using empirical mode decomposition(EMD) method;The research demonstrates that the multipath effects have strong correlation between two successive days,and after the coordinate series being corrected through the first day's multipath model,the new coordinate series generate.The result shows that the stability and the accuracy are markedly improved after multipath effects being removed.
Multipath is the dominant error source in the structural vibration monitoring using GPS. In order to obtain the characteristics of structure natural vibration accurately, both the frequency characteristics of the multipath and the structural vibration are analyzed, then wavelet packet decomposition is employed to extract specifical components in different scales and spectral analysis is adopted for frequency characteristic analysis. Experimental results show that the wavelet packet can be used to separate multipah error and extract the vibration feature effectively. In addition, the actual vibration frequency obtained using GPS conforms its theoretical value and it has high stability.
To satisfy the construction of CHINA Real-Time Precise Positioning Service System, a method of orbit determination of navigation satellite based on priori global information (predicted orbit) is developed. The key is that how the weighting matrices of priori information are computed. Firstly its mathematic model is expressed. Then the characterization of predicted orbit error is analyzed, and a method of achieving the priori information's weighting matrices by Gauss-Markov process is addressed. At last orbit is determined combining the priori information and regional tracking stations' data. Experiment proves that this method is feasible and gets relatively encourage result.
Firstly,we propose a new model namedεE model to measure line segments positional uncertainty,which consider the semi long-axis of the error ellipse at any point on the line segment as the width of the error band,that is,the positional uncertainty of line segment is considered as a set of error circles with the radius of the error ellipse's semi long-axis at any point on the line.Secondly,the analytic expressions of the error band boundary line for the εE model of line segment are deduced,the parameter equations of the error band boundary are gotten.Thirdly,three indexes are given to measure the precision of the line uncertainty based on the εE model: the visualization graph,the average error band width and the error band area.At last,the εE model is compared with the εE model and the εE model.Theory and practice show that εE model is simple in calculation but too limited in the error band width,εE model is scientific in theory but complex in calculation,and model is scientific in theory and convenient in practice though over-width in the error band width.
Compared to existing satellite navigation systems X-ray pulsar navigation can enlarge the service scope.And it can improve the anti-jamming characteristic and autonomous navigation capability.In this paper we analyzed the process of dynamic orbit determination using X-ray pulsar measurement systemically.The basic steps of simulating the observation measurement are presented.Quantification analyses are carried out aimed to study the influence of all kinds of error on orbit determination.Results indicate that calculating spacecraft position and clock error simultaneously can reduce the influence of position of datum mark.Because it can absorb the systematical error.But the calculated clock error can not reflect the intrinsical error of atomic clock.So we need other methods to correct the clock error.Phase error and pulsar visibility are the major influence in orbit determination.And when we want to increase the number of observed pulsar,observation error must be take into account in order avoid the decrease of orbit determination precision.