Research On Several Key Technologies In Webgis

With the rapid development of Internet, WebGIS is applied in more and more fields as a way of displaying and processing spatial information, and so it changes the way of getting, transporting, publishing, sharing and using geographic information. WebGIS is a computer system, which stores, processes and analyzes geographic information in the network environment, after several decades of development, WebGIS has already provided spatial information services for more users in wider area. However, from the application and development of the current WebGIS at home and abroad, the technology is not yet mature. The multi-source and more semantic spatial data makes the system independent of each to spatial information silo and geographic information sharing.Based on the analysis of the relevant research background of the application and development of the current WebGIS, This dissertation makes deep study on the key technologies, which is applied in WebGIS, and successfully applies it into modern digital community. This study mostly including:(1) We proposed a dynamic algorithm of map labeling on the basis of the quadtree. Map labeling problem is one of the most elementary and critical problems in the WebGIS research. At present, map labeling algorithms, which has been published, are abundant such as Discrete Gradient algorithm, Heuristic Method algorithm, back-track algorithm and Simulated Annealing algorithm. But their labeling efficiency is very low, and their time loss is very large. This dissertation, based on making deep study on map labeling algorithms, makes the best of the current software and hardware resources, which is much more advanced, and applies parallel computing technology into map labeling algorithm to greatly improve the efficiency of map labeling.(2) We proposed a mapping method of transforming spatial data into GML document on the basis of XML technology. Traditional WebGIS, which is not able to accurately describe internal data structures, takes HTML as the main expression language of spatial information, but the language can not express multi-source, more semantic, multiscale, and complicated spatial data and can not achieve the query, integration and location of spatial data. GML, which is worked out on the basis of XML by international Open Geospatial Consortium, is a language used to describe spatial data and is established on the basis of Public Geographic Model, at the mean while, it, owing to internal transport and accessibility of GML, is of great significance to the sharing of geographic spatial data. However, spatial data, which is stored by means of geodatabase or data files, causes spatial data not to achieve real resource-sharing. Therefore, this dissertation, which is based on the in-depth study of geodatabase and Geography Markup Language, makes use of the binding technology of Java and XML realize to convert spatial data to GML document.(3) We proposed and designed Web map service model and realize the key models. This dissertation, at first, makes further research and analysis to OpenLayers, which is a map framework, and achieves the TilesMap technology on that basis. After that, We give a profound consideration to map cache technology. At last, we apply the Web map service model into modern digital community successfully.