2006 Vol. 31, No. 12
In the simultaneous adjustment of Astro-geodetic network 1980 and China National GPS geodetic control network 2000,in order to reduce the geodetic observation data to the ellipsoid of WGS84,the technique of remove-restore and Earth gravity model is adopted to refined calculate the deflection of the vertical of 48 919 geodetic point in WGS84,by using the gravity data and 30″×30″ DEM in whole country.And the observation deflection of the vertical of 115 astronomic points in WGS84 is used to the exterior precision check.The total accuracy of the deflection of the vertical in a north-south direction is 1.45″,and that in a east-west direction is 1.50″.The result has been already used in the simultaneous adjustment of two geodetic networks.
This paper simply introduces the theory and method of the boresight misalignment calibration of integrated GPS/IMU,and then a corresponding function model is established.Based on the test flight data,this paper not only validates the validity and the feasibility of the boresight misalignment model,but also analyses the accuracy of direct georeferencing by using the model mentioned above.
It is the core to choose a suitable measure in the classification method based on spectral matching.The spectral similarity scale based on dynamic weight adjustment method,which proposed in this paper,can adaptively adjust the weight of the distance measure and the shape measure according to different conditions,so as to obtain the correct classification.
In the process of reconstruction of textured 3D models of revolution from images,the precise 3D shape of the revolution must be obtained in advance.This can be done using computer vision technique and from symmetry property of potteries.The problem of recovering the 3D shape of a surface of revolution from images is addressed.The algorithm makes use of the symmetry properties of a surface of revolution and its silhouette to rectify the image such that the resulting silhouette exhibits bilateral symmetry.The revolution axis of the surface of revolution is calculated by image parameters and top circle of revolution.The rectified image is then used to recover the contour generator and the object is reconstructed.Experimental results on real images are presented,which demonstrate the effectiveness of the approach.
A method to monitor one Asian dust storm occurred on April 28,2005 by means of four daytime and nighttime MODIS images that are boarded on Terra and Aqua platform is presented.Screening is important for dust storm detection.For daytime Terra and Aqua MODIS data,cloud screening is obtained by using visible and near infrared reflectance,single thermal infrared bright temperature threshold,and the difference of bright temperatures.In the evening TIR bands are only used to remove cloud effects.Then three thermal infrared(TIR),8.5 μm,11 μm,and 12 μm are used,and a tri-spectral technique presented by Ackerman(1997) to extract dust storm areas.It is found that combining brightness temperature differences BT8.5-BT11 with negative BT11-BT12 can detect dust storm.The dust storm areas can be separated from cloud and non-dust areas both on land and on the ocean.Furthermore,dust storm motion can be analyzed by these four scenes MODIS data within 24 h.The result is reasonable by validation with RGB composition method and meteorology data.The study also shows that MODIS data has great potential in dust storm research.
Texture features are often employed as supplementary information in order to supplement the inadequacy of spectral information and increase the classification results of high spatial resolution remotely sensed imagery.However,the dimensions of texture features are always large,which obstruct their overall application in pattern recognition.Independent component analysis is applied to reduce the dimensions of texture features.Compared to the conventional one PCA method,ICA can achieve better classification accuracy and show a better compatibility for different texture features such as SWT,SVD and GLCM etc.
This paper takes an overall review on the former researches firstly.Focus mainly on the concept,types,scaling effect,key problems of DEM scale,as well as its impact on DEM based digital terrain analysis.A few key research topics were put forward through an overall analysis of the research development in recent years,i.e.the property of scale conflict and scale matching between natural and DEM simulated surface;the principle and mechanism of how the spatial scale parameters impact the terrain analysis,the heterogeneity effect in terrain analysis within DEM grid cells.And then,from the view point of regional scale level,both the certainty and uncertainty property in digital terrain analysis should be investigated.In addition,more work should be done to establish a scale depended multi-scaled terrain analysis model as well as DTM scale converting models.Finally,the research development tendency was prospected.
A kind of new methed,which is GPS tidal level measurement,is presented for the determination of instantaneous tidal level at the vessel.The data processing procedure includes the time otfset correction,attitude correction,quality control of GPS height;fusion of GPS height and heave,draft correction,and the filter of GPS tidal level.After these processing, precise tidal level at vessel is determined finally,and the new inethod is also praved by few experiments.
A new method for vessel attitude determination is presented.The attitude determination not only uses the difference between receivers but also uses the transformation relation between local level system(LLS) and body frame system(BFS),thus this method need not calculate ambiguity and possesses high efficiency.Based on the analysis of the result,the validity of the method is proved and the precision of attitude is better than 0.5 degree.
The application of so-called precise point positioning(PPP) method has been limited by the different interval of GPS satellite clock errors provided by IGS or its analysis centres and users.In order to cope with this problem,the commonly used densification methods of GPS satellite clock errors,especially the principle of estimation of high-rate satellite clock errors using IGS ground tracking stations have been analysed and compared.Then the results obtained by different densification method including estimation method are compared with the estimated high-rate satellite clock errors by IGS.After that the satellite clock errors gained by different densification methods introduced have been used for CHAMP orbit determination(OD) employing PPP method combined with dynamic models,and the precision of them are compared as well.The results show that GPS ground tracking data can be used for estimation of high rate satellite clock errors.The precision of estimation is about 0.1 ns to 0.5 ns,which is close to the precision of IGS.The OD precision of LEOs based on PPP method using satellite clock errors obtained by estimation discussed in this paper is less than 10 cm.
A gross-error detecting technique usually used in time series analysis,double lowpasses gross-error detecting technique,is used to detect and repair cycle slips in GPS single frequency carrier phase,the data windows width v_(max) and threshold coefficient k are given.An iterative algorithm utilizing lowpasses to calculate cycle slips is developed.Examples reveal that they are very simple operationally and can detect very small cycle slips.
Starting from the variance-covariance of multi-frequency carrier phase combination's equation,every observation error expression is deduced one by one via the propagation of errors,and the impact of positioning precision with the changing of observation error analyzed.Using only one carrier phase combination to high precision positioning,a method to get the optimal combination is put forward.The result indicates that this method's arithmetic is simple and the precision is excellent,so it can beused for long baseline quick positioning for different precision request.
The estimates of total zenith delay are available using Bernese GPS Software V4.2 based on GPS data every 30 s from the first measurement experiment of a ground-based GPS network in Chengdu Plain of Southwest China during the period of July to September 2004.Then estimates of 0.5 hourly precipitable water vapor(PWV) derived from global positioning system(GPS) are obtained using meteorological data from automatic weather stations.The comparison of precipitable water vapor derived from GPS and those from radiosonde observations is given at Chengdu station,with RMS(root mean square) differences of 3.09 mm.The consistency of precipitable water vapor derived from GPS to those from radiosonde is very good.It is concluded that Bevis empirical formula for estimating the weighted atmospheric mean temperature can be applicable in Chengdu areas because the relationship of GPS PWV with Bevis' formula between GPS PWV with radiosonde method shows a high correlation.The results of this GPS measurement experiment are helpful both for accumulating the study of precipitable water vapor derived from GPS in Chengdu areas located at the eastern flank of the Tibetan Plateau and for studying spatial-temporal variations of regional atmospheric water vapor through many disciplines cooperatively.
Vertical crustal displacements of the Earth's crust in China,due to atmospheric loading effects,are assessed by a spherical harmonic expansion method.The results show that the vertical crustal displacements range up to 20~30 mm,predominantly at the seasonal time scale.The comparison between the seasonal time series of atmospheric loading and the observed GPS daily heights for the six GPS fiducial stations in China indicates that atmosphere is the main cause for the seasonal vertical displacements of the Earth's crust.
In the 3D coordinate transformation,change of two datum system origins ΔX,ΔY,ΔZ,scale change factor λ and three rotate angle θ,,ψ are generally used as parameters,a total of seven changes is called seven-parameter transformation.There are three transformation models,the Buras-Wolf model and the Molodensky model and the WTUSM model,generally used between two datum systems transformation.The linear models is used when the rotate angles are small;however,when the rotate angles are bigger,model errors will be produced relatively.
Basic of GIS and VR technologies,the automatic modeling method which can convert mine roadway system from 2D to 3D is put forward,the mine roadway 2D representation,data extracting and organization,the mine roadway model 3D building are studied,two data organization methods to extract the mine roadway network data are discussed and realized.The prototype system is developed finally,which has the function of 2D mine roadway data import,model transformation,rendering and driving.According to practice of Dazhuang coal mine of Pingdingshan coal group in Henan Province,the mine roadway automatic modeling is realized,and the effect is satisfied.
In GIS Chinese inquiry system,the word meaning ambiguity has brought many troubles in understanding inquiry sentences correctly.The problem is analyzed carefully and a new algorithm is presented based on corpus which can solve ambiguity successfully.As an innovation,A new data structure,called "sentence link stack",is adopted in algorithm.The experimental results show that the algorithm can achieve accuracy of 95% and can offer valid information for the semantic analysis subsystem to draw inquiry targets,inquiry condition,group message and sort message.
The issue of spatial data mining and knowledge in the grid environment are introduced,the produce of spatial knowledge discovery,sharing and fusing,extraction and application is described,an architecture for integrate spatial knowledge application in grid environment is designed,the key technologies of spatial knowledge grid also are discussed.
Ontology is introduced in GIS domain to resolve all kinds of heterogonous issue of GIS.Geo ontology model is designed,and Geo concepts comparing method is proposed,in which concept in Geo Ontology is compared from structure and semantics level to adjust the relation of geo concepts.
Three main visualization issues of present mobile maps arediscussed,i.e.geoinformation unbalance between sheets,symbol fragments and unreasonable updating frequency.Then an adaptive geovisualization method is proposed,which selects geo-objects,calculates adaptive scale,and updates map based on neighborhoods.Experiment result proves this method is feasible and valid to overcome three problems mentioned above.
A new method for the determination of the catastrophe-scale based on the theory of the extended fractal dimension is presented.From the large-scale to the small-scale,the self-similarity of map object descends gradually,and reflects as the change of the map information.Make use of the extended fractal model of inverse "S" can determine the catastrophe-scale between two known scales.
On the basis of the topology of digital circuits,a hierarchical algorithm for circuit simulation is proposed.The main idea is dividing the simulation process into two phases.In the first phase,a logic circuit is structurized and each macroblock is set to the state of either activation or suspension according to the input values of this circuit at the current time.In the second phase,all nodes in each activated macroblock are firstly ordered with breadth-first search pattern.Then all nodes in the macroblock are simulated in reverse order until the output value of the macroblock is obtained.