QoS And Key Issues In WebGIS

This paper is focusing on QoS for WebGIS. Some important QoS factors in GIS services, such as spatial index structures and cache for improving spatial database in query are analyzed for the sake of QoS in WebGIS. WebGIS is an important research area, and the idea of "Software as Service"will take an influence on it. The goal of service is to satisfy the needs of users. The QoS issues include establishing a QoS evaluation system, technologies of supporting QoS, establishing a supporting system of QoS technologies etc. Data Providing Center, Domain Service Center, and User are three key roles in WebGIS. From the viewpoint of users, GIS services are classified into Data Management Service, Data Providing Service, Data Processing Service, Information Searching and Navigating Service, and some other Value-Added Service. The QoS factors of those services are also discussed in the paper. Spatial index is a key issue in massive geo-data processing. In this paper, R* tree, PK tree and Hilbert R tree are analyzed in detail, and the analysis reveals that for the performance of query, PK tree is the best, Hilbert R tree is the second, and R* tree is the last among the three (PK tree has the worst storage performance). Balance PK tree and Heuristic Hilbert R tree are analyzed based on the searches of PK tree and Hilbert R tree aiming to improve the performance of query. And with the concepts of Voronoi Map, the paper presents an outstanding method on the spatial index and its related algorithm to re-improve the performance of query. Cache is another key issue in performance improvement. As the result of the cache theory, this paper issues the concepts of cache-based data proxy. It is used to provide high performance area data service, enhance the flexibility of GIS server and integrated system performance greatly, reduce network load and relieve bottle-neck problem of network bandwidth. Finally, the architecture and design goals of the mapping distribution system of China Geological Library, which is a WebGIS platform developed by our research group, are presented. Many issues concerning of applying in WedGIS application, including fifteen key technical issues in developing GIS are briefly discussed.