Research On WebGIS 3D Visualization Based On Tile Data

From the twentieth century,the Internet has entered a stage of rapid growth,the laying of the network and the speed of the upgrade have increased significantly,which for the development of WebGIS provides a solid environment.As a result,B/S-based GIS systems are becoming more and more services,and in the RIA(rich client)technology,AJAX(dynamic web page)technology and the emergence of mature,WebGIS system is also able to show with the C/S System-like effects and functions.In the mobile device based on the current WebGIS-based map applications are basically desktop application client mode,rarely use a simple browser to achieve the function.On the one hand due to mobile devices,speed and other rigid conditions,on the other hand from the browser to achieve the map application function can not be perfect.But the traditional threedimensional GIS client can not fully meet the open,cross-platform,and more dependent on plug-ins.The construction of three-dimensional WebGIS platform as an open,crossplatform and plug-in model is of great significance to the development of 3D WebGIS.In this paper,through the study of the traditional RIA application model,this paper summarizes the development status and advantages and disadvantages of the geographic information system in this mode.In view of the main problems of RIA mode,the text adopts the HTML5 standard which has been developed in recent years and combined with AJAX dynamic webpage technology.WebGL is used to visualize geospatial data in canvas drawing module,and the system module is optimized in the following two main aspects :(1)In the storage and transmission of tile data,the use of the pyramid structure of the storage,the establishment of a special space for data transmission quadtree indexing mechanism.In order to improve the user operating fluency,for the browser cache technology,the design of the tile data prefetching and caching strategy.(2)In the visualization rendering phase of the map,according to the WebGL image visualization standard,the vertex caching technology is used to simplify the scheduling process of visual data.In the texture visualization part,the Mipmap texture mapping mechanism is adopted based on the user's visual requirement and display efficiency.The commonly used visual culling method is used to design a cutout method suitable for virtual earth for a large number of 3D models.(3)In the final stage,this paper is based on Cesium open source JavaScript library,and according to the needs of the application design to achieve a deployment,cross-platform and other advantages of the WebGIS platform.After testing,this design of the WebGIS platform can be in the PC side and the mobile side can be stable operation,to achieve the desired results.