GIS开发记录(七)：基于Scale切换地图BaseLayer

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gis layer 切换 zoomend scale

实现：最初显示”中国地图（省界）“，放大到一定程度显示”中国地图（地市分界）“，继续放大切换到Google街道地图。

<!DOCTYPE html>
<html>
	<head>
		<title>中国地图</title>
		<meta http-equiv="content-type" content="text/html; charset=UTF-8">
		<link rel="stylesheet" href="css/style.css" type="text/css" />
		<style type="text/css" media="screen">
			body {
				margin:0;
				padding:0;
				height:100%; 
			}
			.bigmap {
				position:absolute;
				left:0;
				top:0px;
				padding:0;
				width:100%;
				height:100%; 
				border:1px solid #333;
			}
		</style>
		<script type="text/javascript" src="js/OpenLayers/lib/OpenLayers.js"></script>
		<script src="http://maps.google.com/maps/api/js?v=3.6&amp;sensor=false"></script>
		<script type="text/javascript">
			var map, layer_province, layer_city, layer_street, vlayer;
			
			// 第一次打开地图的中心位置（经度、纬度）
			var firstLon = 109.33981;
			var firstLat = 33.72419;
			
			/*
			 * 切换地图比例尺设置
			 *	scale1：
			 *  scale2: 省地图和地市地图切换点
			 *  scale3: 地市地图和谷歌街道地图切换点
			 */
			var scale1 = 20000000;
			var scale2 = 10000000;
			var scale3 = 2000000;
			
			var level1 = 1;
			var level2 = 2;
			var level3 = 3;
			var level = level1;
			
				
			function init() {
				// 创建MAP DIV框架
				map = new OpenLayers.Map("map",
					{
						maxResolution: 'auto',
						maxExtent: new OpenLayers.Bounds(
							73.44696044921875, 6.318641185760498, 
							135.08583068847656, 53.557926177978516),
						displayProjection: new OpenLayers.Projection("EPSG:4326")
					});
				
				// 增加中国地图(省界) Layer
				addProvinceLayer()
				
				// 增加中国地图(地市分界) Layer
				addCityLayer();
				
				// 增加Google Street Layer
				addStreetLayer();
				
				// 增加地图Layer切换Register
				addMapRegister();
				
				map.zoomToMaxExtent();
				map.setCenter(new OpenLayers.LonLat(firstLon, firstLat), 0);
				
				map.addControl(new OpenLayers.Control.Scale());
				map.addControl(new OpenLayers.Control.MousePosition());
				map.addControl(new OpenLayers.Control.LayerSwitcher());
			}
			
			function addProvinceLayer() {
				layer_province = new OpenLayers.Layer.WMS(
				    "China:province", "http://10.0.0.239:8081/geoserver/wms",
				    {
				    	layers: "China:province",
				    },
				    {
				    	singleTile: true, //set single label
				    	isBaseLayer: true,
				    	projection: "EPSG:4326",
				    	maxExtent: new OpenLayers.Bounds(
				    		73.44696044921875, 6.318641185760498, 
				    		135.08583068847656, 53.557926177978516)
				    }
				);
				map.addLayer(layer_province);
			}
			
			function addCityLayer() {
				layer_city = new OpenLayers.Layer.WMS(
				    "China:city", "http://10.0.0.239:8081/geoserver/wms",
				    {
				    	layers: "China:city"
				    },
				    {
				    	singleTile: true, //set single label
				    	visibility: false,
				    	projection: "EPSG:4326",
				    	displayInLayerSwitcher: false,
				    	maxExtent: new OpenLayers.Bounds(
				    		73.44696044921875, 6.318641185760498, 
				    		135.08583068847656, 53.557926177978516)
				    }
				);
				map.addLayer(layer_city);
			}
			
			function addStreetLayer() {
				layer_street = new OpenLayers.Layer.Google(
				    "Google Streets", // the default
				    {
				    	numZoomLevels: 18 ,
				    	projection: "EPSG:900913",
				    	visibility: false,
				    	displayInLayerSwitcher: false,
				    	maxExtent: new OpenLayers.Bounds(
				    		-128 * 156543.03390625,
				    		-128 * 156543.03390625,
				    		128 * 156543.03390625,
				    		128 * 156543.03390625)
				    }
				);
				map.addLayer(layer_street);
			}
			
			function addMapRegister(){
				map.events.register("zoomend", map, function(){
					var cur_scale = map.getScale();
					if(cur_scale >= scale2) {
						if(level != level1) {
						    
						    if(level == level2) {
								map.setCenter(map.center.transform(
							       new OpenLayers.Projection("EPSG:4326"),
							       new OpenLayers.Projection("EPSG:4326")
							    ), map.getZoom());
							} else {
								map.setCenter(map.center.transform(
							       new OpenLayers.Projection("EPSG:900913"),
							       new OpenLayers.Projection("EPSG:4326")
							    ), map.getZoom());
							}
						    
						    level = level1;
						    
						    layer_province.displayInLayerSwitcher = true;
							layer_city.displayInLayerSwitcher = false;
							layer_street.displayInLayerSwitcher = false;
							
							map.setBaseLayer(layer_province);
							layer_city.setVisibility(false);
							layer_street.setVisibility(false);
							
						}
					} else if(cur_scale < scale2 && cur_scale >= scale3){
						if(level != level2){
							if(level == level1) {
								map.setCenter(map.center.transform(
							       new OpenLayers.Projection("EPSG:4326"),
							       new OpenLayers.Projection("EPSG:4326")
							    ), map.getZoom());
							} else {
								map.setCenter(map.center.transform(
							       new OpenLayers.Projection("EPSG:900913"),
							       new OpenLayers.Projection("EPSG:4326")
							    ), map.getZoom());
							}
						    
						    level = level2;
						    
						    layer_province.displayInLayerSwitcher = false;
							layer_city.displayInLayerSwitcher = true;
							layer_street.displayInLayerSwitcher = false;
							
							map.setBaseLayer(layer_city);
							layer_province.setVisibility(false);
							layer_street.setVisibility(false);
							
						}
					} else if(cur_scale < scale3){
					   	if(level != level3) {
							map.setCenter(map.center.transform(
						        new OpenLayers.Projection("EPSG:4326"),
						        new OpenLayers.Projection("EPSG:900913")
						    ), map.getZoom());
						    
						    level = level3;
						    
						    layer_province.displayInLayerSwitcher = false;
							layer_city.displayInLayerSwitcher = false;
							layer_street.displayInLayerSwitcher = true;
							
							map.setBaseLayer(layer_street);
							layer_city.setVisibility(false);
							layer_province.setVisibility(false);
							
					    }
					} 
				});
			}
		</script>
	</head>

	<body onload="init()" >
		<div id="map" class="bigmap"></div>
	</body>
</html>

参考：

add, remove base layers depending on zoom, change baselayer

Zoom Control Example

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