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Studies on the Key Technology of Spatial Data Sharing on the Internet
4.3 WebGIS technology and strategy in development of system
4.3.1 The Strategy of Giving Attention to Both Client and Server
In WebGIS, only emphasizing particularly on server and client both have their weakness. Thus this system adopt a synthesizing development strategy, which give attention to both advantage and potential of client and server, reasonably distribute the burden of operation and transmission, sharing the operation capacity, making this system best.
In order to implement synthesizing strategy mention above, the best way is supplying a intellectualized task-distribute function, which make system automatically distribute the task of data processing according to the operation capacity of server and client. But according to current technology level, it is hard to implement such a goal. This system carry out this function by such a way: at first, the data process task or the information serving function is divided into several distinct task-units; then the possible condition of server and client is classified; last we can put forward a task-distribute project according to every classify. Thus when the system operates, it will judge the combination classify of server-client capacity, and decide the task-distribute project.
4.3.2 The WebGIS Client Development Technology based on Java Applet
Web GIS is a typical application system based on Internet. The client of this system was implemented by Java Applet. Java Applet is a little program that runs on the client, which has all advantage of Java, the best of it is it’s strong ability with system. It is embed in web page through HTML, and sent to the computer of user, and then operated by Internet explorer, which greatly improve the information management capacity on the Internet explorer. This system made use of Java Applet, develop a WebGIS explorer based on image-user interface. Users can easily zoom in, zoom out, pan, identify, make thematic map, legend etc.
4.3.3 The WebGIS Server Development Technology based on MapObject(MO)
MO is a WebGIS OCX developed by ESRI, which can be developed by application developer. In this system we make use of VB, MO and MO IMS to develop a program which can receive the request of GET and POST from client, user can make use of this system to easily browse, manage and release dynamic China’s Sustainable Development Information. The server program begin to run when it receive a request from client, client can transform parameter to this program, server response to this request and process with the order and parameter. As the process finished, the processing result will be transformed to client as GIF format. Such mode has much advantage at present considering the slow speed of Internet transmission.
5 Couclusions
Through the construction practice of China’s Sustainable Development Information Sharing System, it is found that the realization of spatial information sharing for public is in great need and possible, though it concerns with many questions such as policy, standard and technologies. This paper talks about some key technology and has put these technologies into the construction practice of China’s Sustainable Development Information Sharing System .Yet there still lie in many problems need to be solved, such as the integration of mathematics model and GIS technology, the Internet application of sustainable development model, spatial index of large amount of spatial information etc.
References
- Chi Tianhe et al. WebGIS Resolution for China’s Sustainable Development Information Sharing System[J]. Resources Science, 2001,23(1). (In Chinese)
- Chi Tianhe et al. Study of Chinese Sustainable Development Information Sharing Network System[J].Journal of Image and Graphics , 1999 supplement. (In Chinese)
- Christian Resch, Peter Jordan, 2001, Characteristics in Data Management within a Scientific Multinational Internet Atlas, Proceedings of ICC 2001 Beijing, China.
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