Openlayers设立ESPG900913作为影射算法

Geoserver默认的地图影射方式是EPSG：4326，但是对于常用的WebGIS来说，常用的影射方式是EPSG：900913，下边的代码用来设置openlayers，通知geoserver使用新的映射算法

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var options = {
		projection: new OpenLayers.Projection("EPSG:900913"),
        maxResolution:156543.0339,
        maxExtent: new OpenLayers.Bounds(-20037508.3427892,-20037508.3427892,20037508.3427892,20037508.3427892),
	    units: "m",
        numZoomLevels: 17,
        displayProjection: new OpenLayers.Projection("EPSG:4326"),
	    controls: []
    }
	
	var map = new OpenLayers.Map('map', options);