ArcGIS api for javascript——用缓存区查询地图

描述

本例展示了如何在另外一个任务里使用一个任务的结果。单击地图查看被单击的点的1公里范围内的缓存（如果需要可以修改这个默认的缓存距离）。也可以看缓存区的这些点的人口普查街区信息。单击一个点查看更多的人口普查街区的信息。

通过GeometryService, QueryTask和一些事件监听器实现了所有的功能:

·GeometryService对象提供访问到ArcGIS Server的几何服务，该服务可以缓冲，投影和简化几何体。
·QueryTask能根据地理或属性条件从地图图层检索要素。在本例中，查询基于地理（在缓存中的区域）。有趣地是，地图图层(人口普查街区组点)不是初始显示在地图上的。对很多这样的查询任务，可以仅仅显示需要的结果元素。
·事件监听器帮助脚本知道事件什么时候发生。监听器说，“当A发生，做B”。监听器可以将几个操作连在一起，象查询后缓存。每当见到dojo.connect()方法，脚本正在监听一个事件。这有一个监听器的例子：

· dojo.connect(map, "onClick", function(evt) {

·            ...

这三个参数表示对象的事件将在哪发生(the map)，本身是什么事件(a mouse click)和当事件发生时运行什么函数。

下面是本例中事情发生的顺序:

1.某人单击地图，触发地图的"onClick"事件

2.几何服务缓存点，触发几何服务的"onBufferComplete"事件

3.缓存的虚线符号被增加到地图上并且查询任务执行，触发查询任务的"onComplete"事件

4.人口普查区被增加到地图上，使用函数sumPopulation统计人口

 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>

 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">

 <html>

   <head>

     <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>

     <meta http-equiv="X-UA-Compatible" content="IE=7" />

     <title>QueryTask with query geometry from another task</title>

     <link rel="stylesheet" type="text/css"

     href="http://serverapi.arcgisonline.com/jsapi/arcgis/1.6/js/dojo/dijit/themes/tundra/tundra.css">

     <script type="text/javascript" src="http://serverapi.arcgisonline.com/jsapi/arcgis/?v=1.6"></script>

     <script type="text/javascript">

       dojo.require("esri.map");

       dojo.require("esri.tasks.query");

       dojo.require("esri.tasks.geometry");

       function init() {

         var startExtent = new esri.geometry.Extent(-95.271, 38.933, -95.228,38.976, new esri.SpatialReference({wkid:4326}) );

         var map = new esri.Map("mapDiv", { extent: startExtent });

         //加载地图时添加查询功能

         dojo.connect(map, "onLoad", initFunctionality);

         var streetMap = new esri.layers.ArcGISTiledMapServiceLayer("http://server.arcgisonline.com/ArcGIS/rest/services/ESRI_StreetMap_World_2D/MapServer");

         //var censusMap = new esri.layers.ArcGISDynamicMapServiceLayer("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Demographics/ESRI_Census_USA/MapServer/");

         map.addLayer(streetMap);

       }

         //初始化功能

       function initFunctionality(map) {

         var queryTask = new esri.tasks.QueryTask("http://sampleserver1.arcgisonline.com/ArcGIS/rest/services/Demographics/ESRI_Census_USA/MapServer/0");

         //确定代理页面使用toJson几何服务并且载荷大于2000

         //如果不是可用的缓冲区，则会请求一个http Post代理.

         esriConfig.defaults.io.proxyUrl= "/arcgisserver/apis/javascript/proxy/proxy.ashx";

         esriConfig.defaults.io.alwaysUseProxy = false;

         //查询

         var query = new esri.tasks.Query();

         query.returnGeometry = true;

         query.outFields = ["POP2000","HOUSEHOLDS","HSE_UNITS", "TRACT", "BLOCK"];

         //几何服务端点

         var gsvc = new esri.tasks.GeometryService("http://sampleserver1.arcgisonline.com/arcgis/rest/services/Geometry/GeometryServer");

         // +++++监听地图的onClick事件+++++

         dojo.connect(map, "onClick", function(evt) {

           map.graphics.clear();

           var symbol = new esri.symbol.SimpleMarkerSymbol();

           var graphic = new esri.Graphic(evt.mapPoint, symbol);

           var params = new esri.tasks.BufferParameters();

           params.features = [ graphic ];

           // 缓冲线性单位（米，公里...）

           params.distances = [ dojo.byId('bufferDistance').value ];

           params.unit = esri.tasks.BufferParameters.UNIT_KILOMETER;

           params.bufferSpatialReference = new esri.SpatialReference({wkid: 102113});

           gsvc.buffer(params);

           dojo.byId('messages').innerHTML = "<b>Creating Buffer Using GeometryService...</b>";

         });

         // +++++监听GeometryService类的onBufferComplete方法+++++

         dojo.connect(gsvc, "onBufferComplete", function(graphics) {

           var symbol = new esri.symbol.SimpleFillSymbol(

                   "none",

                 new esri.symbol.SimpleLineSymbol(

                     "dashdot",

                     new dojo.Color([255,0,0]),

                     2),

                 new dojo.Color([255,255,0,0.25]));

           var graphic = new esri.Graphic(graphics[0].geometry,symbol);

           map.graphics.add(graphic);

           query.geometry = graphic.geometry;

           queryTask.execute(query);

           dojo.byId('messages').innerHTML = "<b>Executing Query with Result BufferGeometry...</b>";

         });

         // +++++监听QueryTask中的executecomplete事件+++++

         dojo.connect(queryTask, "onComplete", function(fset) {

           //创建所选标记的图形

           var symbol = new esri.symbol.SimpleMarkerSymbol();

           symbol.style = esri.symbol.SimpleMarkerSymbol.STYLE_SQUARE;

           symbol.setSize(8);

           symbol.setColor(new dojo.Color([255,255,0,0.5]));

           var infoTemplate = new esri.InfoTemplate("Block: ${BLOCK}","${'*'}");

           var resultFeatures = fset.features;

           for (var i=0, il=resultFeatures.length; i<il; i++) {

             var graphic = resultFeatures[i];

             graphic.setSymbol(symbol);

             graphic.setInfoTemplate(infoTemplate);

             map.graphics.add(graphic);

           }

           var totalPopulation = sumPopulation(fset);

           var r = "";

           r = "<b>The total Census Block population within the buffer is <i>"

                + totalPopulation + "</i>.</b>";

           dojo.byId('messages').innerHTML = r;

         });

       }

       function sumPopulation(fset) {

         var features = fset.features;

         var popTotal = 0;

         for (var x = 0; x < features.length; x++) {

           popTotal = popTotal + features[x].attributes['POP2000'];

         }

         return popTotal;

       }

       dojo.addOnLoad(init);

     </script>

   </head>

   <body class="tundra">

     Zoom to area and click on map to select census block points within the buffered circle.<br/>

     Buffer distance (in kilometers):&nbsp;<input type="text" id="bufferDistance" value="1" size="5"/>

     <div id="mapDiv" style="width: 500px; height:500px;"></div>

     <span id="messages"></span>

   </body>

 </html>

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ArcGIS api for javascript——用缓存区查询地图

描述

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