BeiDou Global Navigation Satellite System(BDS-3)not only performs the normal positioning,navigation and timing(PNT)functions,but also provides featured services,which are divided into geostationary orbit(GEO)and mediu...BeiDou Global Navigation Satellite System(BDS-3)not only performs the normal positioning,navigation and timing(PNT)functions,but also provides featured services,which are divided into geostationary orbit(GEO)and medium earth orbit(MEO)satellite-based featured services in this paper.The former refers to regional services consisting of the regional short message communication service(RSMCS),the radio determination satellite service(RDSS),the BDS satellite-based augmented service(BDSBAS)and the satellite-based precise point positioning service via B2b signal(B2b-PPP).The latter refers to global services consisting of the global short message communication service(GSMCS)and the MEO satellite-based search and rescue(MEOSAR)service.The focus of this paper is to describe these featured services and evaluate their performances.The results show that the inter-satellite link(ISL)contributes a lot to the accuracy improvement of orbit determination and time synchronization for the whole constellation.Compared with some other final products,the root mean squares(RMS)of the BDS-3 precise orbits and broadcast clock are 25.1 cm and 2.01 ns,respectively.The positioning accuracy of single frequency is better than 6 m,and that of the generalized RDSS is usually better than 12 m.For featured services,the success rates of RSMCS and GSMCS are better than 99.9% and 95.6%,respectively;the positioning accuracies of single and dual frequency BDSBAS are better than 3 and 2 m,respectively;the positioning accuracy of B2b-PPP is better than 0.6 m,and the convergence time is usually smaller than 30 min;the single station test shows that the success rate of MEOSAR is better than 99%.Due to the ISL realization in the BDS-3 constellation,the performance and capacities of the global featured services are improved significantly.展开更多
Schema matching is a critical step in the integration of heterogeneous web service,which contains various types of web services and multi-version services of the same type.Mapping loss or mismatch usually occurs due t...Schema matching is a critical step in the integration of heterogeneous web service,which contains various types of web services and multi-version services of the same type.Mapping loss or mismatch usually occurs due to schema differences in structure and content and the variety in concept definition and organization.Current instance schema matching methods are not mature enough for heterogeneous web service because they cannot deal with the instance data in web service domain and capture all the semantics,especially metadata semantics.The metadata-based and the instance-based matching methods,in the case of being employed individually,are not efficient to determine the concept relationships,which are crucial for finding high-quality matches between schema attributes.In this paper,we propose an improved schema matching method,based on the combination of instance and metadata(CIM)matcher.The main method of our approach is to utilize schema structure,element labels,and the corresponding instance data information.The matching process is divided into two phases.In the first phase,the metadata-based matchers are used to compute the element label similarity of multi-version open geospatial consortium web service schema,and the generated matching results are raw mappings,which will be reused in the next instance matching phase.In the second phase,the designed instance matching algorithms are employed to the instance data of the raw mappings and fine mappings are generated.Finally,the raw mappings and the fine mappings are combined,and the final mappings are obtained.Our experiments are executed on different versions of web coverage service and web feature service instance data deployed in Geoserver.The results indicate that,the CIM method can obtain more accurate matching results and is flexible enough to handle the web service instance data.展开更多
Various sensors connected to the World Wide Web are used to obtain real-time hydrological observations.Thus,real-time management and utilization of such distributed in situ observations in the cyber-physical environme...Various sensors connected to the World Wide Web are used to obtain real-time hydrological observations.Thus,real-time management and utilization of such distributed in situ observations in the cyber-physical environment becomes possible.A Sensor Observation Service(SOS)chaining Web Feature Service(WFS)method is proposed to integrate geographical reference observation data collected by a hydrological Sensor Web into a virtual globe.This method hides the complexity of a series of information and service models in the Sensor Web realm to enable the integration of heterogeneous distributed hydrological data sources into a Spatial Data Infrastructure(SDI).The core components-a dynamic schema transformer and automatic information extractor-were designed and implemented.The SOS schema is matched to WFS schema that uses the schema transformer dynamically.The information extractor extracts and serves features automatically,conforming to standard SOS operations for observation retrieval and insertion.Feasibility experiments conducted on the Jinsha River tested this proposed method.Results show that the proposed approach allows the integration of SOS servers into legacy applications that have a higher degree of availability within many SDIs.However,this is accompanied with the drawback that only a limited part of the SOS functionality is available to clients.展开更多
For geospatial cyberinfrastructure-enabled web services,the ability of rapidly transmitting and sharing spatial data over the Internet plays a critical role to meet the demands of real-time change detection,response a...For geospatial cyberinfrastructure-enabled web services,the ability of rapidly transmitting and sharing spatial data over the Internet plays a critical role to meet the demands of real-time change detection,response and decision-making.Especially for vector datasets which serve as irreplaceable and concrete material in data-driven geospatial applications,their rich geometry and property information facilitates the development of interactive,efficient and intelligent data analysis and visualization applications.However,the big-data issues of vector datasets have hindered their wide adoption in web services.In this research,we propose a comprehensive optimization strategy to enhance the performance of vector data transmitting and processing.This strategy combines:(1)pre-and on-the-fly generalization,which automatically determines proper simplification level through the introduction of appropriate distance tolerance speed up simplification efficiency;(2)a progressive attribute transmission method to reduce data size and,therefore,the service response time;(3)compressed data transmission and dynamic adoption of a compression method to maximize the service efficiency under different computing and network environments.A cyberinfrastructure web portal was developed for implementing the proposed technologies.After applying our optimization strategies,substantial performance enhancement is achieved.We expect this work to facilitate real-time spatial feature sharing,visual analytics and decision-making.展开更多
基金supported by the National Natural Science Foundation of China(41931076,L1924033,and 41904042)National Key Research and Development Program of China(2020YFB0505800)。
文摘BeiDou Global Navigation Satellite System(BDS-3)not only performs the normal positioning,navigation and timing(PNT)functions,but also provides featured services,which are divided into geostationary orbit(GEO)and medium earth orbit(MEO)satellite-based featured services in this paper.The former refers to regional services consisting of the regional short message communication service(RSMCS),the radio determination satellite service(RDSS),the BDS satellite-based augmented service(BDSBAS)and the satellite-based precise point positioning service via B2b signal(B2b-PPP).The latter refers to global services consisting of the global short message communication service(GSMCS)and the MEO satellite-based search and rescue(MEOSAR)service.The focus of this paper is to describe these featured services and evaluate their performances.The results show that the inter-satellite link(ISL)contributes a lot to the accuracy improvement of orbit determination and time synchronization for the whole constellation.Compared with some other final products,the root mean squares(RMS)of the BDS-3 precise orbits and broadcast clock are 25.1 cm and 2.01 ns,respectively.The positioning accuracy of single frequency is better than 6 m,and that of the generalized RDSS is usually better than 12 m.For featured services,the success rates of RSMCS and GSMCS are better than 99.9% and 95.6%,respectively;the positioning accuracies of single and dual frequency BDSBAS are better than 3 and 2 m,respectively;the positioning accuracy of B2b-PPP is better than 0.6 m,and the convergence time is usually smaller than 30 min;the single station test shows that the success rate of MEOSAR is better than 99%.Due to the ISL realization in the BDS-3 constellation,the performance and capacities of the global featured services are improved significantly.
基金This work was supported by the National Natural Science Foundation of China[grant number 41201393]the Open Research Fund of State Key Laboratory of Information Engineering in Surveying,Mapping and Remote Sensing of Wuhan University[grant number 14I03].
文摘Schema matching is a critical step in the integration of heterogeneous web service,which contains various types of web services and multi-version services of the same type.Mapping loss or mismatch usually occurs due to schema differences in structure and content and the variety in concept definition and organization.Current instance schema matching methods are not mature enough for heterogeneous web service because they cannot deal with the instance data in web service domain and capture all the semantics,especially metadata semantics.The metadata-based and the instance-based matching methods,in the case of being employed individually,are not efficient to determine the concept relationships,which are crucial for finding high-quality matches between schema attributes.In this paper,we propose an improved schema matching method,based on the combination of instance and metadata(CIM)matcher.The main method of our approach is to utilize schema structure,element labels,and the corresponding instance data information.The matching process is divided into two phases.In the first phase,the metadata-based matchers are used to compute the element label similarity of multi-version open geospatial consortium web service schema,and the generated matching results are raw mappings,which will be reused in the next instance matching phase.In the second phase,the designed instance matching algorithms are employed to the instance data of the raw mappings and fine mappings are generated.Finally,the raw mappings and the fine mappings are combined,and the final mappings are obtained.Our experiments are executed on different versions of web coverage service and web feature service instance data deployed in Geoserver.The results indicate that,the CIM method can obtain more accurate matching results and is flexible enough to handle the web service instance data.
基金This work has been supported in part by the National Basic Research Program of China(973 Program)under Grant 2011CB707101by the National Natural Science Foundation of China under Grant 41023001,41171315,and 41021061+1 种基金by the program for New Century Excellent Talents in University under Grant NCET-11-0394by National High Technology Research and Development Program of China(863 Program)under Grant 2012AA121401.
文摘Various sensors connected to the World Wide Web are used to obtain real-time hydrological observations.Thus,real-time management and utilization of such distributed in situ observations in the cyber-physical environment becomes possible.A Sensor Observation Service(SOS)chaining Web Feature Service(WFS)method is proposed to integrate geographical reference observation data collected by a hydrological Sensor Web into a virtual globe.This method hides the complexity of a series of information and service models in the Sensor Web realm to enable the integration of heterogeneous distributed hydrological data sources into a Spatial Data Infrastructure(SDI).The core components-a dynamic schema transformer and automatic information extractor-were designed and implemented.The SOS schema is matched to WFS schema that uses the schema transformer dynamically.The information extractor extracts and serves features automatically,conforming to standard SOS operations for observation retrieval and insertion.Feasibility experiments conducted on the Jinsha River tested this proposed method.Results show that the proposed approach allows the integration of SOS servers into legacy applications that have a higher degree of availability within many SDIs.However,this is accompanied with the drawback that only a limited part of the SOS functionality is available to clients.
基金a National Science Foundation(NSF)CAREER award BCS-1455349,an NSF award PLR-1504432,and an OGC Testbed13 grant.
文摘For geospatial cyberinfrastructure-enabled web services,the ability of rapidly transmitting and sharing spatial data over the Internet plays a critical role to meet the demands of real-time change detection,response and decision-making.Especially for vector datasets which serve as irreplaceable and concrete material in data-driven geospatial applications,their rich geometry and property information facilitates the development of interactive,efficient and intelligent data analysis and visualization applications.However,the big-data issues of vector datasets have hindered their wide adoption in web services.In this research,we propose a comprehensive optimization strategy to enhance the performance of vector data transmitting and processing.This strategy combines:(1)pre-and on-the-fly generalization,which automatically determines proper simplification level through the introduction of appropriate distance tolerance speed up simplification efficiency;(2)a progressive attribute transmission method to reduce data size and,therefore,the service response time;(3)compressed data transmission and dynamic adoption of a compression method to maximize the service efficiency under different computing and network environments.A cyberinfrastructure web portal was developed for implementing the proposed technologies.After applying our optimization strategies,substantial performance enhancement is achieved.We expect this work to facilitate real-time spatial feature sharing,visual analytics and decision-making.