Research And Achievement Of Progressive Vector Map Transmission Over The Web

In the high-speed Internet era,the rapid transmission of vector map promotes the popularization of the Web Map Service.Compared with the traditional raster map,vector map is full of richer content,more personalized form,and much more flexible operation,which makes people no longer satisfied with the raster map,but tend to vector maps.However,influenced by the complex structure of the vector maps and the limitation of network bandwidth,the application and development of vector map transmission over the Web is restricted.In order to effectively solve the efficiency problem of vector map transmission in the network,a novel data transmission technology,progressive vector map transmission,is adopted in this paper.This new transmission mode refers the idea of progressive image transmission,progressive triangular mesh transmission and progressive audio and video transmission.Following the “transmission and display synchronization” method,it realized on-demand transmission,reduced data redundancy,and improved the efficiency of spatial data transmission.In this paper,the progressive linear vector map transmission over the Internet is discussed from the following aspects:(1)Use relevance triangle to separate polyline into a series of curves,and express the visual saliency and visual information of polyline by the visual characters of relevance triangle.On the basis of human visual perception principle,use visual saliency to guide the layering of feature sets,and use visual information to guide the simplification of the features.(2)According to the amount of visual information,to convert BLG-Tree structure,which is constructed by D-P simplification,into linear incremental vector sequences.In order to guarantee the smoothness of the visual perception among different scales,to reorganize the linear incremental vector sequences,and build a new multi-scale vector map as per the rules of visual invariance of information increments between different scales.(3)According to the linear incremental vector sequences after reorganizing,to establish a model of multi-scale vector increments which is based on the location reservation.In this model,the fusion rules are set up between the incremental sequences of adjacent scales,so as to improve the efficiency of progressive vector map transmission in the Web and the multi-scale vector map reconstruction on the client side.Multi-scale vector increments organization and vector map reconstruction are the two core contents of the progressive vector map transmission,which determine the efficiency of vector map progressive transmission and reconstruction.Based on above research methods,in this paper,to establish the B/S model of progressive vector map transmission system,and realize the multi-scale visual information measurement,polyline simplification,multi-scale vector increments reconstruction and vector map rebuilding on the client.The experimental results showed that the segmentation method of polyline based on the relevance triangle can well keep the spatial shape and the level of detail information of polyline;visual hierarchy information can guide the simplification of polyline and the linear serialization of increments;the way of vector increments organization based on a location reservation can effectively improve the efficiency of progressive vector map transmission across the Web and vector map reconstruction on the client.