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Studies on the Key Technology of Spatial Data Sharing on the Internet
4 Key Technology studies
4.1 Client-Server Information Transmission Protocol In order to realize the information exchange between client and server,a set of information transmission protocol need to be set up. Protocol is composed of request and response. Protocol content need fully reflect system function and some control process. So, system function needs to be clearly defined. From the analysis of system function,we can classify these function as data request, query, analysis, help, control and metadata. Every protocol’ structure is clearly defined. This protocol adopts orientate-object thinking,making the progress of information exchange abstract as the progress of sending information and receiving information. Both client and server act as request-driving.  Figure 3 The Procedure of Informatin Transmission When a request-object was formed,the request-object was in charge of forming a response-object, then the response-object will finish process automatically. Such a process is same both in client and server, the only difference lie in the different response-object. For example, as for browser,whole request and response progress at server is transparent,it has a message-processing center,which form request, send request and acquire response according to user request. 4.2 Spatial Information Presentation and Integrating Analysis The presentation of spatial information includes vector and grid two forms. In this system, we adopt the way that combing vector and grid. As for normal information query, explore, users can operate very easily as they are operating desktop. When it concerns with the calculating analysis of data,it need the help of porosity server to decide adopting which way. So, for all registered system model, the describing information need to be supply. Users can make spatial query or attribute query by their way,query result can be display by map or chart. For those statistic data that can be used to make thematic, it can supply making-chart tool, users can make style and position setting, such as legend, map name, map symbol , color,so they can make full understanding of the information they acquire. The analysis function in this system includes spatial analysis and statistic analysis. Spatial analysis concerns with more spatial operation, which can be finished by GIS server. The problem mainly lie in two aspects:One is how to embed the spatial analysis function from other special GIS software into this system, the other is how can present model be shared among users? As for the first question, we use the interface supplied by manufacture factory to use corresponding module or directly obtain the data after analysis. As for the second question, such a question can be solved by establish a set of interface mechanism, and model is requires to embed into system operation with the least change, the future extension should be supplied. As for statistical analysis, many analysis tools are supplied to users, they can use such tools to make statistical analysis aiming at a specific variable. |