The Changes accumulation model for streaming map data transferring over web

The streaming transfer method which makes data immediately available application during the progress of transfer becomes a welcome transfer way over Web. The progressive transmission of map data provides the users with a self-adaptive strategy to access remote data. It not only speeds up the Web transfer but also offers an efficient navigation guide in information acquisition. The key technology in this transmission is the efficient multiple representation of spatial data and pre-organization on server site. This paper aims at vector data offering a new multiple representation model called changes accumulation model, which considers the spatial representation from one scale to another scale as an accumulation of set of changes. The difference between two consecutive representations is recorded in a linear index and through gradually addition or subtraction realizes the progressive transmission. As an example, the progressive transmission of area feature based on changes accumulation model is investigated in the paper. The model is built by hierarchical decomposition of polygon into series of convex hulls or bounding rectangles and through component of the decomposed elements to accomplish the progressive transmission.