Progressive Transmission of River Network

The progressive transmission of vector map data requires an efficient multi-scale data model to process the data into a hierarchical structure.This paper presents such a data structure of river network without redundancy of geometry for progressive transmission.For a given scale,the river network display has to settle two questions.One is which river objects to be selected and the other is what detail to be visualized for the selected rivers.This study combines the T pfer law and the BLG-tree structure to answer the above two questions simultaneously.At the level of object element,the river branches are sorted on descending significance grade decided by watershed area to support the river selection by the T pfer law.At the level of geometric detail,the river branch is splitted into segments by joint points with the organization of the linear BLG-tree to export a good graphic representation at a given scale.Based on the data structure,a WebGIS is established to provide progressive transmission services of river networks.