基于SVG的矢量WebGIS地图高级查询功能的实现

The realization of advanced search functions on SVG-based vector WebGIS map

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,利用它提供的图形对象可实现矢量WebGIS。查询是GIS的一个重要交互功能,由于SVG内置了对JavaScript的支持,所以客户层可通过JavaScript对DOM的操作实现地图的高级查询功能。当在浏览器中打开SVG或SVGZ文件时,SVG图形作为浏览器的一个嵌入对象出现,由SVG插件对其在指定区域显示。如果用户对地图进行某些查询操作,此时可以通过JavaScript函数来获取SVG地图对象及其内部的图形属性,通过不同的查询机制和查询方式,向用户提供地图查询功能,显示用户查询的相关信息,同时由SVG插件刷新对它的显示。

SVG is a sort of markup languages based on XML,it is used to describe two dimension vector graphics and vector/raster mixed graphics.Though SVG is not a standard that be made in order to the release of spatial data of geography,but a lot of characteristics of it can be widely applied to WebGIS,thus the vector WebGIS can be realized.Because SVG describe vector picture by the format of simple text,so the data amount of SVG is usually very little,and SVG can be compressed through GZIP,so the WebGIS that be constructed based on SVG can lighten transmission load of the network and accelerate the display pace of the map.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.