Advanced Progressive Transmission for Spatial Data in Web based GIS

초록

In conventional Web Geographic Information System(GIS), there are drawbacks of high waiting time and low accessibility since the following query has to be waited until all the spatial data is completely transmitted. In addressing theses problems, this paper proposes a progressive transmission method which can reduce waiting time and increase accessibility. The proposed method has the following steps: first of all, it selects significant vertices of geographic objects based on an algorithm, Priority_Order_Estimation(POE). Secondly, these selected objects are inserted to the data structure, Priority_Order_Queue(POQ), which allows a client to view, to request and occasionally to reject a spatial data, rather than waiting for the whole map to arrive. Thirdly, the progressive transmission step is processed, where significant vertices of POQ are sent from server to client one by one. At the final step, if necessary, the entire spatial data set of SENDOBJSP, which is a transmission structure, are transmitted so as that the original map is exactly displayed. The performance of the realized system in the proposed method has been evaluated according to the factors such as system response time and client storage space. Comparing with the conventional method, the system response time is decreased about twenty-two percent and client storage space is reduced about twenty-one percent. As a result, the performance improvement, fast response time and less client storage usage, over simply sending the most significant vertices without compression is achieved. In addition, system response time is reduced and less client storage space is used in initial time. Therefore, the proposed method can give a much contribution in support of Web based GIS applications since many of Internet users use only low-bandwidth connections to the Internet.