Distributed Network Of Geographic Information Systems Research

With the review of GIS history, the main characteristic of webGIS is given, then the situation of webGIS in software platform and application is given in detail. The limitations of webGIS with a centered server for managing large computationally intensive data-set problems are well known. Distributed computing is an important direction of webGIS in future. Distributed webGIS is a combination of distributed computing technology and webGIS.In this article, three questions are discussed: firstly, definition and theory of distributed webGIS; secondly, main technology of distributed webGIS; the last, designing and implement a distributed webGIS prototype.Firstly, the framework and definition of distributed webGIS are given. After comparison of the main distributing object computing technology, two architectures of distributed webGIS with CORBA and message queue manager are introduced.Secondly, how to manage distributed spatial data is a key problem in distributed webGIS. After comparison of two models for spatial data: map layer model and Oriented-object model for spatial feature. It shows the interoperability of spatial data is necessary and how to construct distributed spatial database and other correlated questions are analyzed. We summarized manage model for map data, connection of heterogeneous database, storage of map data, spatial index, spatial query for map data and management of remote sensing image data in distributed webGIS.The architecture model of webGIS changes from the simple 3-tie model to n-tie interoperable model and step-by-step spatial data processing model. Some important questions for client/server architecture in distributed webGIS are discussed such as how to reply simultaneous requests form clients, web security, digital signature and level of details for spatial data in clients.At lastly, a distributed webGIS prototype is designed and implemented with CORBA technology. The design flow is as follows: design of distributed spatial database, design of interface for the system, design of application servers and design of clients. Spatial data are stored in database as blob fields, spatial query is based on high efficient spatial index method: R+ tree. Clients can query images according to its features such as color, texture and edge. The main functions of the prototype are as follows: vehicle supervision in Internet by GPS, integration of multi-source spatial data, projection transformation and making thematic map from spatial data. Multi-source spatial data include vector map in database, DEM grid, remote sensing mage and vector map uploading from clients. Visualization and interactivity are boosted up with distributed webGIS technology. Distributed webGIS will make an important role in digital earth.