2015 Vol. 40, No. 8
Traditional centralized high-precision navigation and positioning services cannot meet thepublic users'demand for reliability,scalability and service diversity.This paper describes cloud posi-tioning,and the way in which various positioning resources are managed and integrated comprehen-sively to optimize technology convergence and resources sharing,based on cloud technology.We pres-ent the cloud positioning,framework and discuss the realization of several traditional positioning tech-nologies through the cloud positioning platform,i.e.,GNSS Network RTK,GNSS wide area precisepointing positioning,Wi-Fi positioning,communication base-station positioning and others.We arguethat,compared with the traditional technologies,cloud positioning has more advantages in scalability,reliability,the maintenance cost and feasibility.Using the cloud positioning platform,not only canusers enjoy various high precision positioning services,but also optimizes allocation of resources toprovide personalized services.An efficient business model and technical approach will allow for thepopularization of precise navigation and positioning services.
The problem of precise orbit determination was studied using three kinds of HY2Aobserva-tional data of GPS,DORIS and SLR separately and together in February 2013.Comparing the derivedorbits with CNES precise orbits,the results show:(1)Using GPS,DORIS and SLR data separately,the GPS data to determine the radial orbit of average accuracy was 1.3cm,the three-dimensional posi-tion was about 6.2cm;the radial average accuracy of the DORIS solution was 1.6cm,and slightlyworse than the results of GPS;and SLR to determine the radial orbit of the average accuracy was 2.3cm.(2)Comparing the CNES orbits with the orbits derived from GPS,DORIS and SLR data togeth-er,the difference of RMS was 1.2cm in the radial direction,and the three-dimensional position was6.5cm.Compared to GPS solution,the combined three kinds of data cannot improve the accuracy ofthe derived orbit,but it is helpful to keep the calculated orbit in relative stability.(3)Using SLR datawith high elevation passes(above 60degrees)to validate the accuracy of the GPS/DORIS orbit,wefound the RMS of the estimated biases to be about 2.5cm,showing that HY2Adata can determinethe centimeter-level orbit.
A Power Inversion adaptive algorithm(PI)is often used to get the nulling beamform inGNSS jamming techniques.When the signal to interference ratio is 80dB,a PI algorithm can accu-rately identify the direction of jamming at high resolution.However,a large ribbon nulling will formaround the direction of the RF interference signal in the algorithm.If the signal to interference ratioreduces to 20dB,the resolution of the interference signal will seriously deteriorate.The multiple sig-nal classification(MUSIC)algorithm has super-resolution features;it can achieve power minimizationthrough the signal subspace and noise subspace orthogonal principles.A two-dimensional spectralpeak search technology is used in searching the azimuth and elevation of interference to accurately esti-mate the DOA and effectively distinguish the desired signal and the interference signal.When the sig-nal to interference ratio is high,the suppression depth from the MUSIC-PI algorithm is significantlybetter than the traditional power inversion algorithm.In a low signal-to-interference ratio condition,the MUSIC-PI algorithm is still valid when suppressing the interference in the right direction,but thepower inversion algorithm cannot discriminate the direction of interference accurately.Computer sim-ulation results show the effective and robust performance of the MUSIC algorithm in the GNSS jam-ming field.
Satellite altimetry data with different spatial and temporal resolution has different effects oncalculation of the deflection of vertical,thus the Jason1waveform data and Cryosat data are combined.After the preprocessing of waveform retracking and the time-varying effect weakened,the deflection
Mobile mapping technology can be used to acquire geospatial data efficiently,accurately andat low cost,it is one of the most advanced technologies for geospatial data acquisition.A preconditionfor acquiring high quality point clouds using mobile laser systems is that the mobile system be wellcalibrated.Ground control points are used in the common method to calibrate mobile laser systems,but these methods as inflexible and it is labor intensive to collect ground control points.In this paper
An enhancement method of active faults merged with DEM,panchromatic,multispectral re-mote sensing images is proposed.Interpretation sighs of active faults are established based on spatialfeature variation of terrain and water.A newly Youjiang secondary active fault,40km long,NW-tren-ding extending,is discovered between Bama-Mashan fault and the Youjiang fault.Combined withseismic geological data,the interpretation results are compared and verified.In the process of imagemerging,the KL transformation,HIS transformation,Multiplicative transformation,Brovey trans-formation and Wavelet transformation are completely compared.With principle components analysisof merged image,Multiplicative transformation is selected to produce enhanced image and interpreta-tion map.The feature of active fault is outstanding ultimately.
Presently CCD and SAR are the two main space-borne remote sensor systems;most stereoimaging research focuses on the homology between stereoscopic pairs of these sensors.This paperpresents a heterogeneous stereo imaging technology that can incorporate any CCD and SAR image withabsolutely different mechanisms and certain overlapping area into a uniform stereo imaging process system.First,methods to refine geometry model parameters and pixel-precision to automatically match CCD and SARimages are briefly reviewed.Based on this review,a heterogeneous stereo imaging model was constructed andcalculated.All link-road error propagation and accuracy assessment approaches were analyzed.These stepsgave full play to the complementary advantages of CCD and SAR sensors without the harsh restrictions of tra-ditional homology methods.At last,Experiments based on different combination of imaging data were per-formed to ensure that our scheme can be reliably applied to stereo imaging applications over any targetarea.With the input of 3mSAR and 1mCCD images,20m-plane and 30m-vertical precision resultscan be achieved using the technology proposed in this paper.
High-dimensional data interpolation is a basic content of big data analysis.The computa-tional cost of traditional Kriging is of order n3,which means computational complexity grows as thethird power rate along with the increase number of the observations.So Kriging computing time canhardly meet real-time applications.Thus,Fixed Rank Kriging(FRK)rises in response.To achievehigh computing speed,it simplifies computational complexity by reducing the dimensions of large-di-mensional matrix.Under the background of big data analysis,this paper uses FRK to do the statisti-cal modeling and implement interpolation analysis with the global MODIS temperature.It also givesout Root-Mean-Square standardized which equals to 1.0003through the cross-validation method,indi-cating that FRK can provide high accurate interpolation result.On the side of computational efficien-cy,with increasing data,the computational cost of FRK increases as a slow and steady speed while or-dinary kriging tends to an exponential growth.The conclusion can be drawn from two points above,that is,FRK can reduce computational complexity and shorten interpolation time with high predictionaccuracy when compared with ordinary kriging.
At present SAR polarimetric calibration algorithm are assumed to satisfy reciprocity fromdistributed targets.But not all distributed targets satisfy the principle of reciprocity.Aiming to solvethis problem,this paper presents a method to calibration based on reciprocity judgment of distributedtargets.According to the angle between the polarization scattering matrix and the reciprocal matrix ofeach pixel,we select pixels with small angle as the initial reciprocity calibration samples.Then,onthe basis of the coherence of targets,some pixels are selected as the final calibration samples.CECT-38X-band fully polarimetric data were completed by combining a typical calibration algorithm and se-lected distributed targets using the proposed method.Experiments show that this method,using dis-tributed targets,can be well applied to SAR polarimetric calibration.
In this article,an algorithm for vehicle detection is proposed using the improved histogramof oriented gradients(HOG)features,in which a fusion of weighted multi-channel HOG features isemployed.First,the color image is enhanced by the method based on the mean of brightness.Afterthat the image is remapped into HSV color space.In consequence,the multi-channel HOG feature isobtained by combining the adaptive-weight HOG feature for each channel.Finally,the support vectormachine(SVM)is trained by such feature to detect the vehicles.Experiments prove the robustnessand precision of this algorithm and it reaches the requirement for all-weather vehicles detecting interms of the one using the traditional HOG features.
Considering the demands for precise spatial relationships and effective 3Dvisualization in 3Dplanning approval,two solutions of rapid and mass building roof texture generation is presented inthis paper.In the first solution,the correspondence of object space and image space is built based onthe collinearity equation of perspective projection,then,the best roof texture for texture mapping canbe selected considering the optical axis direction,occlusion relation and image resolution.In the sec-ond solution,the roof texture database is built and used to synthesize roof texture with the smartmatching technology.The experimental results with the 3Dcity models of Changzhou demonstratethat two sets of solutions for roof texture generation can meet the requirements of rapidly reconstruc-ting texture of building.
A new segmentation approach of polarimetric synthetic aperture radar(PolSAR)data is pro-posed based on mean shift and spectral graph partitioning.First,Mean-shift algorithm is used to gen-erate the over-segmentation of PolSAR image.In order to extract edge information,we apply a set ofdetectors based on the Wishart distribution with a hypothesis testing method that has fully consideredthe polarization information in PolSAR images.Then,a similarity matrix is constructed based on theover-segmentation results and image edge information.The graph partitioning process is performed u-sing the normalized cut criterion.With this method,we improve the segmentation efficiency of spec-tral graph partitioning based on the over-segmentation results generated by Mean-shift.The quality ofsegmentation results is also improved as a result of the global optimization of spectral graph partitio-ning algorithm.We applied this method on Radarsat-2full polarization images and evaluated the seg-mentation results.The experiement showed that this scheme can realize PolSAR segmentation effec-tively,speed up the original algorithm,and also demonstrates a better result than eCognition’s Multi-resolution segmentation approach.
Based on the characteristics of the digital radio mondiale(DRM),a new method of arraycalibration for high-frequency passive radar(HFPBR)by using frequency reference signal of directwave is proposed.Firstly the signal structure of DRM is introduced,while the feasibility of take fre-quency reference signal as the calibration source is demonstrated.Secondly,taking into account the e-lectromagnetic environment and time-varying non-stationary propagation characteristics,a method ofchoosing high quality direct wave period by the shift-invariant antenna pairs is proposed.Finally,as-sist by the known DRM transmitter position,we utilized this method deal with measured direct wavedata which propagate in surface wave mode and sky wave mode,compared the result of array calibra-tion value with known single frequency signal source.The results showed that the amplitude andphase compensation method in DRM-based HFPBR is effective.
Image registration is an important step in the process of super-resolution image reconstruc-tion.In practical applications when the rotation angle is greater than 6°,the Keren algorithm will cre-ate greater registration error,and its computational complexity as the amount of image shift will growseveral times larger.Considering the Vandewalle algorithm,its registration under certain rotation an-gle conditions is a certain advantage,but the overall registration accuracy is lower than the Keren al-gorithm.Aiming to solve the problems of two existing registration algorithms,we combined Adjust-ment of Indirect observations with Constraints to proposed an improved image registration method.The proposed algorithm calculates the rotation parameters and translation parameters using theVandewalle algorithm between the images.Then,the rotation parameters are included as the knownvalues used in Keren algorithm,while the translation parameters are taken as observations,Using theadjustment of indirect observations with constraints iterative shift parameter correction values wecame to the final registration parameters.Our studies show that the algorithm avoids errors stemmingfrom the Taylor series expansion of angle when using the Keren algorithm In the case of large angles,improving the registration accuracy with better reconstruction results.
With the wide application of Internet,there is more and more geotagged text information.Nevertheless,such data is currently browsed in Geographical information systems through externallinks,requiring frequent zooming,panning,and click operations.Meanwhile,other methods can noteffectively express spatial relationships.A tag cloud mapping method—a tag cloud-based visualizationfor geotagged text information is presented in this paper.We provide an overall implementationprocess for the method and design and implement a prototype based on the real-life data sets of Ten-cent Microblog.We focus on designing cartogram algorithms for point and polygon features,the ex-traction of keywords and frequency and the display rule models for different scales and different timesin the label placement algorithms.This method can help users rapidly make sense of the importantconcepts and grasp main features and developing trends in a large amount of geotagged text informa-tion.
It is difficult to acquire small-scale spatial variation of intra-urban air pollutants fromsparsely distributed monitoring sites;therefore,a land use regression model was used to generate ahigh-resolution map of summertime PM2.5concentrations in Wuhan.Four spatial factors had high lev-els of correlation to PM2.5average concentrations were identified using a bivariate correlation analysis;road length in buffers with 1000mradius(x2),area of waters in buffers with 500mradius(x5),areaof construction land in buffers with 500mradius(x9)and point sources(x18).These four spatial fac-tors together with meteorological data(monthly average temperature and monthly precipitation)wereused as independent variables to build a multiple linear regression(MLR)model with PM2.5monthlyaverage concentration as the dependent variable.The R2 of the regression was 0.905,and the adjustedR2 was 0.885.We then built a grid at a resolution of 2km×2km.The PM2.5concentration for eachcell of the grid was estimated using the MLR equation.A high resolution map of PM2.5concentrationof Wuhan in summer was generated based on this grid and spatial interpolation results showing thehigh-resolution distribution of PM2.5concentration.There were three high-value centers of PM2.5con-centration,the Qingshan industrial zone,the north industrial zone,and Hanxi building material mar-kets area in Hankou.There were two low-value centers located at large lakes or in areas with largepercentage of water in south Hanyang and south Wuchang.
This paper presents a structured DEM generalization by catchment area combination.Thevalley catchment areas are used as the link between the abstract conception of valley and concreteDEM grid points.The minor valley branches are deleted by the Tpfer law and the valley catchmentareas are combined based on the deleted valley network.Then the resulting DEM is interpolated basedon the catchment boundary line(containing three types of basic terrain skeleton information:ridge,mountain and saddle)and the valley line.Experiments show that a DEM reconstructed by this methodcan delete minor terrain characteristics while preserving main characteristics.
Cartograms is a new approach for statistical data visualization.However,drastic diversity oflocal data leads to failures when we apply existing cartogram-making algorithms on grid statistic datawithin urban scale.To address this problem,we design an index for measuring the scale effect of gridstatistic data.The scale effect index well describes the restriction effect and representation effect of1104武汉大学学报·信息科学版2015年8月 multi-scale grid data.Moreover,based on the scale effect index,we modify the diffusion-based meth-od developed by Gastner and Newman in 2004.The modified algorithm is not sensitive to local diversi-ties of grid statistic data,and area cartograms achieved by this algorithm well keep the density-equali-zing condition.We apply this algorithm in making gridded population cartograms from 100mgrid Bei-jing census data,and results show the reliability of the algorithm,which can be used for producing ar-ea cartograms of statistic data.
Concerning that it mainly depends on manual adjusting to realize the match between delimi-tation line and real terrain,this paper proposes the general solution to automatically complete above-mentioned match based on Least-Cost Path Analysis,and studies its key technology.First,terrainfeatures network is built via reverse search based on dangling terrain features grid and processed underthe guidance of delimitation theory.Then,cost layer is constructed for Least-Cost Path Analysis inorder to carry out above automatic match.Finally,some experiments are conducted so as to analyzeand estimate automatic match,which validates that automatic match studied in the article is feasibleand reliable.Additionally,some suggestions are provided for delimitation.
A spherical Voronoi diagram of point sets,line sets and area sets can be well handled byGDG-based(GDG:Global Discrete Grid)algorithms.However,the grid data volume and the timeconsumed for generating spherical Voronoi diagrams increases exponentially with the growth of theGDG levels,which leads to lower efficiency at higher levels.To overcome these deficiencies,a multi-level QTM-based(QTM:Quaternary Triangular Mesh)algorithm is proposed.Firstly,a sphericalVoronoi diagram is generated in a lower level.Then,the triangles that form the Voronoi boundariesare subdivided to get Voronoi diagrams at higher levels.The results show that a spherical Voronoi di-agram of higher levels can be generated by this algorithm more efficently than those single-level algo-rithms;as it was improved about 22and 25times at Level 9.
The SDOG-based Earth System Spatial Grid(SDOG-ESSG)is an important tool and methodin the Earth System Science and spatial information domains.This paper focuses on the key problemof transformation between the grid code of SDOG-ESSG and the existing spatial reference,the trans-formation between Spheroid Coordinates System (SCS)and the grid code of SDOG-ESSG.Six col-umn-row-layer number systems were brought in and related formulas were derived.Based on this andthe bit-interleaving method of Morton code,forward and backward transformation algorithms weredeveloped.The time efficiency of both algorithms was analyzed theoretically and experimentally.Theresults show that:a)both algorithms are very high efficient,and the time consumption is linear to theprinciple subdivision level and the further subdivision level of SDOG-ESSG,where the time complexi-ty is O(n);and(b)approximately 106～107times of transformation operations can be done in one sec-ond under current personal computer.Each transformation operation is identical to 101～102 divisionoperation in time.
Based on the natural similarity between the parallel computing features of cellular automataand the parallel computing architecture of the CUDA,a dam-break flood routing computing modelbased on GPU-CA is proposed.Key technologies including cellular automata(CA)model of dam-break flood routing,GPU model mapping method,calculation optimization method,and GPU/CPUcollaborative implementation for dam-break flood routing simulation and analysis are discussed in de-tail.Finally,aprototype system was developed and a case study region selected for carrying out a pre-liminary experiment.As compared to the CPU-CA model computing,the experimental results showedthat the dam-break flood routing computing based on GPU-CA model can greatly improve the computing efficiency,and also ensured the validity of the simulation results.Speedup can be improved by in-creasing the cellular grid resolution.When the cellular grid size was 10m,the speedup of model calcu-lation reached 15.9times,which can support real-time simulation analysis and risk assessment fordam-break flood routing.
In order to achieve the mutual enhancement between surveillance videos and 2Dgeo-spatialdata,a modal including geometric and content mapping is proposed.Firstly,based on the pin-holecamera model of photogrammetry and computer vision,we assume the ground is composed of multipleplanes and propose a mapping model.The mapping model has clear physical meaning,convenient andflexible.Through the model,the videos and 2Dgeospatial data can be mutually projected.Secondly,because the true ground is not flat,undulation has an impact on the mapping between videos and 2Dgeospatial data,a formula for the impact is provided.Thirdly,the objects in videos are larger nearbyand smaller at far distances.In order to get the real space of each pixel,we propose an indicator,vide-o spatial resolution and discuss the spatial distribution.The model is suitable for multiple planes butnot suitable for complex geographic scenes.