Seiwebgis System And Realization

WebGIS, which can be simply defined as the CIS on the internet, is the technology to consummate and extend traditional CIS functions using internet technology. It has profound theory meaning and application value to research and realize WebGIS system based on J2EE architecture. "SeiWebGIS" system comes from "Dalian spatial information infrastructure construction" project, and its final object is to be one WebGIS platform.First, the paper discusses the definition of WebGIS and its characteristics which are different from other traditional CIS, then introduces its actuality and direction. In the sequel, the paper introduces several common WegGIS building technology, and compares their advantages and shortages. Aiming at the actuality that current WebGIS systems are mostly based on the black-box data model, the paper introduces the step-service model to access spatial data sources on the web, which is presented by Allan Doyle.Chapter Four is the keystone of this paper. This section introduces in detail the function demand, system architecture, data index technology and storage method, data organization and scheduling strategy, graphics processing and so on. Data storage is the foundation of the whole system, the paper puts forward the optimized quadtree index technique, which effectively solve the large-data index problem. Based on the index technique, the paper presents a asynchronous data-read algorithm that using block as the minimum scheduling unit, as well as the data-remove algorithm which is combined with the nearest-longest unused algorithm and the highest priority algorithm, thus insure the high efficiency of spatial data scheduling. To reduce the development cost and risk, the method is to encapsulate the data scheduling module of SeiGIS series products into a CORBA server which can be called by SeiWebGIS system.