腾讯地图getZoom缩放级别计算

 JS计算缩放地图缩放级别

		//根据经纬极值计算绽放级别。
		function getZoom (maxLng, minLng, maxLat, minLat) {
			var zoom = ["50","100","200","500","1000","2000","5000","10000","20000","25000","50000","100000","200000","500000","1000000","2000000"]//级别18到3。
			var pointA = new BMap.Point(maxLng,maxLat);  // 创建点坐标A
			var pointB = new BMap.Point(minLng,minLat);  // 创建点坐标B
			var distance = map.getDistance(pointA,pointB).toFixed(1);  //获取两点距离,保留小数点后两位
			for (var i = 0,zoomLen = zoom.length; i < zoomLen; i++) {
				if(zoom[i] - distance > 0){
					return 18-i+3;//之所以会多3，是因为地图范围常常是比例尺距离的10倍以上。所以级别会增加3。
				}
			};
		}