Research On Visual Optimization Method Of Vector Tile Under Large-scale Features

With the continuous development of map service,vector tile map has become the mainstream solution of electronic map with the advantages of rich color expression,strong interactive ability and efficient data transmission,which is widely used in land,transportation,water conservancy and so on.However,when the features are distributed unevenly or the zoom level of the map is low,the amount of features contained in the vector tiles will increase significantly,and the amount of features loaded by the browser in a single time will even reach a million level.Such a large-scale quantity of features greatly affects the rendering efficiency and style visualization of the map.Cartographic generalization can effectively reduce the number of features,but the existing cartographic generalization methods are difficult to achieve automation based on the global characteristics of data and do not consider from the perspective of vector tiles.At the same time,the visualization process of map style is complicated and error-prone,and there are few researchs of real-time tile rendering optimization based on dynamic attributes.Based on the above problems,this thesis studies tile generation and map visualization,which aims to optimize the visualization method of vector tiles under large-scale features.The research contents are as follows:(1)Based on the concept of vector data organization and vector tile model,combined with tile generation and tile rendering principle,an integrated scheme from generation to visualization of vector tiles is proposed.In the aspect of tile generation,study the key technologies of efficient rendering oriented automatic cartoraphic generalization and pluggable algorithm mechanism,tile and default style generation,which lays the foundation for subsequent visualization services.In the aspect of map visualization,the vector tile style visualization scheme based on static attributes is designed to solve the problem of low efficiency of style writing and real-time preview.The strategy of vector tile rendering based on dynamic attributes is developed toimprove the real-time rendering efficiency of map style with changing attributes.(2)Develope an automatic cartoraphic generalization method of point,line and polygon under large-scale features.As for point,this thesis puts forward the point feature aggregation strategy based on regular grid and the point feature selection strategy under adaptive grid to solve the problem of symbol overlap in the rendering of point features under vector tiles.As for line and polygon,This thesis puts forward the concept of index of feature importance(IFI),which is used as the sorting basis for deletion of features,then defines the map similarity and the comprehensive effect index of cartography,which retains the main information of map and effectively improve the rendering efficiency.Based on the data of traffic lights,roads and land use layers about China from OSM,the performance and effect comparison experiment of single tile before and after automatic cartography is designed.The experimental results show that while retaining the main information of the map,the rendering results of point features are more concise and beautiful.The rendering efficiency of line features is increased by 1-2 times,and that of polygon features is3-4 times.(3)Design and build a large-scale feature oriented vector tile visualization prototype system.Using distributed storage computing,multi-source vector data organization,efficient map visualization engine and other development technologies,relizes the distributed generation of vector tiles and efficient visualization,forming the overall interactive logic of large-scale vector data from extraction to management and finally to application display,which proves the visual optimization method proposed in this thesis is feasible and effective in practical application.