Research On The Distributed Geographic Information Service Based On Component

With the development of information technique and the prevalence of internet, the schema of traditional Geographic Information System software is being migrated from the integration of system and functions to Servicess and applications. ESRI corporation pointed out that Distributed Geographic Information Services (DGIS) is one of two important directions of GIS. Many countries and international organization have paid much attention to the research on DGIS. At the same time, the DGIS can be applied in many fields, such as agriculture, forestry, ocean, environment, traffic, communication, urban construction, education and military, etc. Consequently, DGIS is a very new and important research direction of GIS.This dissertation is based on two practical application systems and mainly focuses on the key techniques of DGIS and its implementation. From the view of higher efficiency of system, this research discusses the management, compression and progressive transmission of spatial data and experiments on them; Under the frame of .NET of Microsoft and following the relevant criterions of OpenGIS, this research employs Web Services and COM/DCOM/COM+ to design and implement a component based DGIS architecture; designing and implementing relative components of client and server; In the end, two practical application systems are build to verity the availabilities of the theories and the techniques mentioned above. The main research work is as follows:(1) Summarization and analysis of current distributed component techniques. This dissertation detailedly analyses the current distributed component techniques, suchasCOM/DCOM/COM+, CORBA, RMI/EJB/J2EE and Web Services, and then compares them with each other and gives the adventages and shortcomings of them, which privides the proofs of applying special component techniques for this research.(2) Research on high performance ognization and management of spatial data. Whether for traditional desktop GIS or for DGIS based on internet, high performance ognization and management of spatial data are important. Based on case studies, this research sperates spatial data into basic spatial data and industrial spatial data and then proposes the framework of multilevel spatial index. In addition, a concrete database table is designed for martial symbol data.(3) Research on compression and progressive transmission of vector data. Compression and progressive transmission of vector data is helpful for improving the running efficiency of system, however there is little domestic research on it and there are few research papers even in international research journal. This dissertation reviews the compression and reduction methods of vector data and then designs two main compression methods of vector data: improved classic Douglas-Peucker andwavelet based compression algorithm. This dissertation also presents the improved DP algorithm based on BLG tree to progressively transmit vector data on internet and designs the architecture and file format of progressive vector transmission. Especially, this research tests the two methods and compares the experimental results which show that the efficiency of system with progressive vector transmission can be improved much.(4) Under the frame of .NET and following the criterion of OGC, this research proposes a three tiers distributed system architecture using Web Services and COM/DCOM/COM+ and analysis the advantages of it. The case study shows that the system architecture can satisfactorily meet the need of distributed application program for large numbers of users' accessing.(5) Design and implementation of a high performance map component. Following the simple object criterion of OGC, this research employs ATL to implement an exquisite map component. This component is small-size and has high performance, which is suit for being downloaded and running on internet. Presently, this component has been integrated into Geobeans 5.5, the excellent domestic WEBGIS software.(6) Design and implementation of component for martial symbol editing. Based on the martial symbol library, this research employs ATL to implement an all-purpose component for martial symbol editing. This component has a strong and flexible interface so that it can be easily and fast integrated not only with map components of Geobeans but also with prevalent map components, such as MapObjects^ MapX to develop application system about martial symbol editing. Presently, this component has been integrated into Geobeans 5.5, the excellent domestic WEBGIS software.(7) Research on design of server-side component and distributed deployment. This dissertation discusses the important issues, such as system architecture of server-side component, principle of distributed deployment, the implementing techniques based on Web Services and the advised cautions in deploying distributed component.(8) Design and implementation of two practical application systems. As a main researcher, the writer designs and accomplishes two practical application systems: the WEBGIS based command control system for forest fire fighting (for forest armed forces, Beijing) and the WEB based martial symbol editing and command control system(for logistics and command control college, People's Liberation Army, Beijing). The former system won the national silver award in electing excellent domestic application project of GIS in 2004. As is known, the value of any research is embodied by application, and almost three years' research work of the writer was carried out surrounding the practical application.