Progressive Transmission of Vector Map on the Web

This paper presents a method of progressive transmission of vector data on the web based on the Changes Accumulation Model. The model considers the spatial representation from one scale to another scale as an accumulation of a set of changes, and the change can take place at three levels: layer, object and geometric detail. Taking the example of drainage network, this paper gives a new storage structure without redundancy of geometry for progressive transmission. At the level of object element, the river branches are sorted on descending significance grade which is estimated by drainage area. At the level of geometric detail, a river branch is splitted into sections, and each section is organized by a linear BLG-Tree, enabling selecting the proper representation for a given scale. For a request scale, the optimal number of the needed river branches can be determined by the Topfer rule in map generalization. Furthermore, the good graphic representation of each river branch can be obtained by selecting nodes of the linear BLG-Tree. Finally, this paper presents a browser/server architecture for progressive transmission based on WFS (Web Feature Service), GML (Geography Markup Language) and AJAX (Asynchronous JavaScript and XML). To support the progressive transmission and refinement, some extensions are made to WFS and GML standards. * Corresponding author.