描述
本例展示了如何在地图里指出显示的缓存或切片的细节等级（LODs）。当打开示例地图，可以看到一些来自ArcGIS Online ESRI_Imagery_World_2D图层的影像。这个应用程序配置这个影像仅LOD 0 - 11是可见的，即使在源缓存中存在其他的等级。直接放大最终会切换到来自ArcGIS Online CSP_Imagery_World_2D图层的详细的user-contributed影像。该应用程序配置了user-contributed影像仅仅在LODs 12 -17是可见的。
本例为地图创建了一组LODs，这组LODs合并了在多个缓存服务中的LODs。在ArcGIS JavaScript API 1.2版本以前，仅仅能是使用增加的第一个服务的LODs。 注意设置在ArcGISTiledMapServiceLayer中的displayLevels[]如何转为图层的tileInfo.lods。随后，他们被联接为一个自定义的地图的一组LODs(customLods[])。
放大时可以显示自己的一组数据，而缩小时显示ArcGIS Online或一些其他数据。要执行这个图层转换的类型，匹配的缓存切片方案是必需的。在本例中的两个服务使用ArcGIS Online的缓存切片方案。
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> 3 <html> 4 <head> 5 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/> 6 <meta http-equiv="X-UA-Compatible" content="IE=7" /> 7 <title>放大时切换图层</title> 8 <script type="text/javascript">djConfig = { isDebug:true };</script> 9 <link rel="stylesheet" type="text/css" href="http://serverapi.arcgisonline.com/jsapi/arcgis/1.6/js/dojo/dijit/themes/tundra/tundra.css"> 10 <script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=1.6"></script> 11 <script type="text/javascript"> 12 dojo.require("esri.map"); 13 dojo.require("esri.layers.agstiled"); 14 15 var customLods = []; 16 var loadCount = 0; 17 18 function init() { 19 20 var esriImageLayer = new esri.layers.ArcGISTiledMapServiceLayer( 21 "http://services.arcgisonline.com/ArcGIS/rest/services/ESRI_Imagery_World_2D/MapServer", 22 {displayLevels:[0,1,2,3,4,5,6,7,8,9,10,11]} 23 ); 24 if (esriImageLayer.loaded) { 25 addLods(esriImageLayer); 26 }else { 27 dojo.connect(esriImageLayer,"onLoad",addLods); 28 } 29 30 var cspImageryLayer = new esri.layers.ArcGISTiledMapServiceLayer 31 ("http://services.arcgisonline.com/ArcGIS/rest/services/CSP_Imagery_World_2D/MapServer", 32 {displayLevels:[12,13,14,15,16,17]}); //Levels at which this layer will be visible 33 if (cspImageryLayer.loaded) { 34 addLods(cspImageryLayer); 35 } else { 36 dojo.connect(cspImageryLayer, "onLoad", addLods); 37 } 38 39 } 40 41 //用层次细节填充数组 42 function addLods(layer) { 43 customLods = customLods.concat(layer.tileInfo.lods); 44 loadCount++; 45 46 if(loadCount === 2) { 47 initMap(); 48 } 49 50 } 51 //创建地图并且用自定义的层次细节 52 function initMap() { 53 var map = new esri.Map("map",{ 54 lods:customLods, 55 extent:new esri.geometry.Extent(-82.05,34.87,-80.05,34.99,new esri.SpatialReference({wkid:4326})) 56 57 }); 58 59 dojo.connect(map,"onExtentChange",changeScale); 60 map.addLayer(esriImageLayer); 61 map.addLayer(cspImageryLayer); 62 63 } 64 //报告哪一层将被显示 65 function changeScale(extent,delta,outLevelChange,outLod) { 66 dojo.byId("scale").innerHTML = "LOD Level: <i>" + outLod.level; 67 if (outLod.level < 12) { 68 dojo.byId("visibleLayer").innerHTML = "Layer:<i>ESRI_Imagery_World_2D</i>"; 69 }else{ 70 dojo.byId("visibleLayer").innerHTML = "Layer:<i>CSP_Imaery_World_2D</i>"; 71 } 72 } 73 74 dojo.addOnLoad(init); 75 </script> 76 77 </head> 78 79 <body > 80 <div id="map" class="tundra" style="position: relative; 900px;height: 600px;border: 1px solid #000"> 81 <span id="scale" style="position: absolute;right: 10px;bottom: 10px;z-index: 100;color: yellow;font-size: 150%;"></span> 82 <span id="visibleLayer" style="position: absolute;right: 10px;bottom: 10px;z-index: 100;color: yellow;font-size: 150%;"></span> 83 </div> 84 <p>Zoom in to the city below to switch to user-contributed imagery from ESRI's content sharing program</p> 85 </body> 86 </html>