Study On Progressive Transmission Of Vector River Network Data

Progressive transmission is a new type of network transmission for spatial data, and is also a hot topic in GIS research. Progressive transmission can effectively solve a contradiction between the limited bandwidth of network and infinite growth of spatial data. Moreover, it implements the visualization of spatial data from important levels to secondary levels, and from low-resolution scales to high-resolution scales during the process of display at client. Progressive visualization meets the users'demands that the spatial data can be browsed, indexed and analyzed from different views and levels.The purpose of this paper is to implement progressive transmission of river network data at object levels and geometric features levels. Main contents include:First, related work to progressive transmission of vector map is reviewed and summarized. Second, an "Accumulating Changes Based on Initial Version" model which is suitable for multi-scale data organization of progressive transmission at server is deeply analyzed. Third, several description factors of river-tree structure are introduced in detail, and then a new selection approach for objective rivers during the process of progressive transmission is presented. Fourth, river curves are simplified by using an improved Visvalingam-Whyatt algorithm, and then the multi-scale visualization is achieved. Fifth, a new algorithm for storage, index and progressive transmission of river data is elaborated by combining whole river structures and interior geometric features. Finally, a client/server system for progressive transmission of river network vector data is implemented in term of the proposed research results.The experiment results show that the proposed algorithms not only decrease the amount of data transmission tremendously and increase the efficiency of web release, but also achieve good adaptive visualization effects of river data.