| The development of digital earth demand GIS must realize data share and develop WebGIS technology, and the growing up of network technology has injected new vigor into development of GIS. GIS and network technology merge so as to form the integrated platform of GIS that based on Internet technology naturally become an important direction and hot Question for present GIS research field.But present WebGIS products are mostly based on traditional GIS systems software that is constructed using CGI or Server API and generally need to operate backstage one or more GIS application program. This kind of mode has only solved the problem of publishing space information on Web, it has not redesigned and optimized for the Web environment, so it can't meet people's demands on function and efficiency. In addition, the nowaday WebGIS exist defect on the space data model, and XML has the variety of the source of data and agility, flexibility and adaptability of many kinds of application, it brings the new opportunity for WebGIS.With the fast development of WebGIS, fast transmiting and viewing the electronic map by way of vector in WebGIS is a focus that GIS research at present. And SVG based on XML can just solve the problem that the vector is published in WebGIS.ASP.NET is a part of MicroSoft .NET, it has powerful developing function of Web. SVG is one kind of markup languages that is used describing two dimension vector graphics and vector/grid mixed graphics, it is a kind of expansion application program that XML expressed the graphics and picture in the network in essence. Utilizing ASP.NET strong function of Web development and the vector transmiting and displaying function of SVG, we can comparatively construct WebGIS that the function is strong, performance is comparatively optimizing and data is safe and the development cost is cheap.This thesis has designed a kind of WebGIS platform solution based on ASP.NET and SVG technology.Through the research to the specific realization of the solution, can educe the following conclusion:(1) It introduce ASP.NET, Web Service and SVG technology into the design and realization of WebGIS, it realize very good combination of powerful Web developing function of ASP.NET and vector transmiting and displaying of the map through using SVG, at the same time, through publishing and registering the Web Service that is already defined can also realize sharing of the data resources on GIS database server of this system, we can also search relevant Web Service that has published and registered in Internet to realize integration of the other land data through citing it.(2)Designing and realizing WebGIS by introducing multistage cache and security mechanism of ASP.NET, not only improve the whole operational efficiency of WebGIS through the cache of client and server, but also guarantee WebGIS that is developed in this way to run safely in Internet.(3)The geographical data are kept in the corresponding database of the database server according to the integrated structure or XML/GML way, after the server receives the request from client, for the integrated structure database, real-timely extracting the data of the corresponding range from the database by analysis and changing it into XML/GML by Web Service that has been defined, for XML/GML database, direct extracting the data,then changing XML/GML that has been gained by the front two way into SVG through XSLT and transmiting SVGZ to the client browser to display after the compresseing of GZIP for SVG, if user does not have new data asked, user is just carrying on enlarging, shrinking, roaming operation etc, then these oprations can only use SVGZ file that has been already download to the client with .aspx pages, and not need transmiting these data moreover, on the basis that the data amount of the vector transmitting is small, it has further reduced the transmitted data amount,it has further improved transmitting and displaying efficiency. So the way not only can guarantee background data is safe and reliable but also has higher efficiency.(4)The solution adopt the space database of the integrated structure to organize and store GIS data or adopt XML/GML database to store GIS data, thus utilize RDBMS to achieve unified management for the space data and attribute data, it offer geographical information query service with higher efficiency for the client, at the same time, it improve management and maintenance efficiency for GIS data.Another, it can realize integration of the data of many sources through carrying on the mode mapping and changing the different data source into XML/GML data. Finally, converting different space data to XML/GML based on text form, thus integrating the different structure space data to the form of XML/GML, thus realizing sharing and operating each other between the space data.(5)Do not need to buy expensive WebGIS development software, such as MapXtreme, ArcIMS etc. we can realize WebGIS, the development cost is cheap.Through developing concrete WebGIS, it has proved the solution has the characteristic that data is easily integrated and shared, the amount of transmitted data is small, transmiting velocity is fast, performance is comparatively optimizing and the data is comparatively safe and the development cost is cheap etc. |
