基于SVG的矢量WebGIS性能的优化

SVG是一种基于XML的用来描述二维矢量图形和矢量/栅格混合图形的标记语言,GIS中的空间数据都可由它提供的图形对象实现,并且SVG内置了对JavaScript的支持,而SVG可通过DOM解析映像成内存中的树型结构,所以客户层可通过JavaScript对DOM的操作实现对地图的缩放、漫游、查询、图层控制等交互操作,从而实现矢量W ebGIS。由于SVG用简单的文本来描述GIS矢量空间数据,因此数据量相对较小,且SVG支持GZIP压缩,压缩后的SVGZ可减少75%-80%,从而减轻了网络传输负载,加快了地图的显示速度。若能配合使用服务器端和客户端缓存技术,使用优化DOM文档解析与提升图像渲染性能的方法,则可进一步提高基于SVG的矢量W ebGIS的性能。

The optimization on the performance of vector WebGIS based on SVG

SVG is a sort of markup vector graphics and vector/raster mixed languages based on XML, it is used to describe two dimension graphics, the spatial data of GIS can be realized with the graphic object of it, SVG can support JavaScript by itself, and SVG can be mapped into the tree structure in the memory through DOM, so the client can operate DOM by JavaScript to realize the scale, the roam, the inquire, the control for the map layers, etc. thus the vector WebGIS can be realized. Because SVG describes the vector spatial data of GIS with the simple text, the data amount are relatively small, and SVG supports GZIP compression, the data amount can reduce 75% - 80% from SVG to SVGZ after compressing, so the transmission load of network can be lightened and the display pace of map can be accelerated. If we can cooperate using the cache technology of the server and client, using those methods that can optimize DOM parsing and promote the performance of image render, the performance of vector WebGIS based on SVG can be further improved.