描述
使用ArcGIS Server 幾何服務（geometry service）來對繪制在地圖上的圖形生成緩沖區。幾何服務能夠在基於瀏覽器的應用程序中執行緩沖操作（buffering），投影要素（project feature），計算可測量值。
利用幾何服務創建緩沖區之前，需創建一個BufferParameters（緩沖參數）的實例，並且明確緩沖距離（distance），單位（unit）以及坐標系統（spatial reference）。通過傳入這個參數（parameters）和一個當緩沖執行完成時調用的回調函數（callback）來調用緩沖（buffer）功能。
geometryService.buffer(params,function(features){showBuffer(features)});
注意：
-
在下面的例子中使用了ArcGIS JavaScript API 自帶的繪制工具條，通過工具條產生的幾何（geometry）作為緩沖操作的輸入幾何。如果幾何的類型是多邊形，則程序會在其作為參數進行緩沖處理之前進行簡化（simplify）操作。這是用來找出那些邊界線相交的非法拓撲多邊形。簡化操作能強行將這些多邊形轉變為合法的多部分的要素（multipart features）。
-
這個示例醫用了一個代理頁面，以防幾何的GET請求超過了某些Web瀏覽器強加的2000字符的限制。有關如何建立自己的代理頁面，請參閱代理頁面的說明。
<!DOCTYPE html>
<!--<html lang="en"> 加入lang會導致dojo的樣式錯誤-->
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no">
<title>Buffer</title>
<link rel="stylesheet" href="https://js.arcgis.com/3.20/dijit/themes/claro/claro.css">
<link rel="stylesheet" href="https://js.arcgis.com/3.20/esri/css/esri.css">
<style>
html, body {
height: 100%;
width: 100%;
margin: 0;
padding: 0;
overflow:hidden;
}
#leftPane{
color:#000;
width:250px;
padding-bottom:15px;
}n
#map{
padding:0;
}
.details{
font-size:14px;
font-weight:600;
padding-bottom:20px;
}
button{
margin:2px;
cursor:pointer;
}
</style>
<script src="https://js.arcgis.com/3.20/"></script>
<script type="text/javascript">
var map,tb;
// AMD模塊
require(["dojo/dom",
"dojo/_base/array",
"dojo/parser",
"dojo/query",
"dojo/on",
"esri/Color",
"esri/config",
"esri/map",
"esri/graphic",
"esri/geometry/normalizeUtils",
"esri/tasks/GeometryService",
"esri/tasks/BufferParameters",
"esri/toolbars/draw",
"esri/symbols/SimpleMarkerSymbol",
"esri/symbols/SimpleLineSymbol",
"esri/symbols/SimpleFillSymbol",
"dijit/layout/BorderContainer",
"dijit/layout/ContentPane",
"dijit/form/Button",
"dojo/domReady!"
],
function(dom, array, parser, query, on, Color, esriConfig, Map, Graphic, normalizeUtils, GeometryService, BufferParameters, Draw, SimpleMarkerSymbol, SimpleLineSymbol, SimpleFillSymbol){
// dojo根據dom標簽的屬性實例化控件
parser.parse();
// esriconfig : The default values for all JS API configuration options.
esriConfig.defaults.geometryService = new GeometryService("https://utility.arcgisonline.com/ArcGIS/rest/services/Geometry/GeometryServer");
// proxy 用於跨域
esriConfig.defaults.io.proxyUrl = "/proxy/";
esriConfig.defaults.io.alwaysUseProxy = false;
//dojo用於事件綁定
on(dom.byId("clearGraphics"),"click",function(){
if(map){
map.graphics.clear();
}
});
// dojo 的選擇器
query(".tool").on("click",function(evt){
if(tb){
tb.activate(evt.target.id);
}
});
map = new Map("map",{
basemap:"streets",
center:[-111.5,39.541],
zoom:7
});
// map加載成功后然后初始化工具條
map.on("load",initToolbar);
// evtObj 屬於 事件參數
function initToolbar(evtObj){
tb = new Draw(evtObj.map);
tb.on("draw-complete",doBuffer);// 已經不建議使用draw-end事件了，改為draw-complete
}
function doBuffer(evtObj){
tb.deactivate();
var geometry = evtObj.geometry,
symbol;
switch(geometry.type){
case "point":
symbol = new SimpleMarkerSymbol(SimpleMarkerSymbol.STYLE_SQUARE,10,new SimpleLineSymbol(SimpleLineSymbol.STYLE_SOLID, new Color([255,0,0]), 1), new Color([0,255,0,0.25]) );
break;
case "polyline":
symbol = new SimpleLineSymbol(SimpleLineSymbol.STYLE_DASH,new Color([255,0,0]),1);
break;
case "polygon":
symbol = new SimpleFillSymbol(SimpleFillSymbol.STYLE_NONE,new SimpleLineSymbol(SimpleLineSymbol.STYLE_DASHDOT,new Color([255,0,0]),2),new Color([255,255,0,0.25]));
break;
}
// 顯示畫的幾何：形狀 + 樣式
var graphic = new Graphic(geometry,symbol);
map.graphics.add(graphic);
// 設立緩沖參數
var params = new BufferParameters();
params.distances = [dom.byId("distance").value]; // 參數為數組
params.outSpatialReference = map.spatialReference;
params.unit = GeometryService[dom.byId("unit").value];
// Normalizes geometries that intersect the central meridian or fall outside the world extent so they stay within the current coordinate system. Only supported for Web Mercator and geographic coordinates.（子午線規范化工具）
normalizeUtils.normalizeCentralMeridian([geometry]).then(function(normalizedGeometries){
var normalizedGeometry = normalizedGeometries[0];
if(normalizedGeometry.type === "polygon"){
// 規范化多邊形幾何操作
esriConfig.defaults.geometryService.simplify([normalizedGeometry],function(geometries){
params.geometries = geometries;
// 進行緩沖操作
esriConfig.defaults.geometryService.buffer(params,showBuffer);// ShowBuffer is callback function
});
}else{
params.geometries = [normalizedGeometry];
esriConfig.defaults.geometryService.buffer(params,showBuffer);
}
});
}
function showBuffer(bufferedGeometries){
// 設置緩沖區顯示樣式
var symbol = new SimpleFillSymbol(
SimpleFillSymbol.STYLE_SOLID,
new SimpleLineSymbol(
SimpleLineSymbol.STYLE_SOLID,
new Color([255,0,0,0.65]),2),
new Color([255,0,0,0.35])
);
// dojo 數組遍歷
array.forEach(bufferedGeometries,function(geometry){
// 顯示地圖繪制樣式
var graphic = new Graphic(geometry,symbol);
map.graphics.add(graphic);
});
}
});
</script>
</head>
<body class="claro">
<div data-dojo-type="dijit/layout/BorderContainer"
data-dojo-props="gutters:'true', design:'sidebar'"
style="width:100%;height:100%;">
<div id="map"
data-dojo-type="dijit/layout/ContentPane"
data-dojo-props="region:'center'">
</div>
<div id="leftPane"
data-dojo-type="dijit/layout/ContentPane"
data-dojo-props="region:'left'">
<div class="details">Pick a tool and draw on the map. The drawn graphic will be buffered based on the specified parameters.</div>
<button type="button" class="tool" id="line">Line</button>
<button type="button" class="tool" id="polyline">Polyline</button>
<button type="button" class="tool" id="freehandpolyline">Freehand Polyline</button>
<br/>
<button type="button" class="tool" id="polygon">Polygon</button>
<button type="button" class="tool" id="freehandpolygon">Freehand Polygon</button>
<br/><hr />
<div><b>Buffer Parameters</b></div>
Distance: <input type="text" id="distance" size="5" value="25" />
<select id="unit" style="width:100px;">
<option value="UNIT_STATUTE_MILE">Miles</option>
<option value="UNIT_FOOT">Feet</option>
<option value="UNIT_KILOMETER">Kilometers</option>
<option value="UNIT_METER">Meters</option>
<option value="UNIT_NAUTICAL_MILE">Nautical Miles</option>
<option value="UNIT_US_NAUTICAL_MILE">US Nautical Miles</option>
<option value="UNIT_DEGREE">Degrees</option>
</select><br />
<button type="button" id="clearGraphics">Clear Graphics</button>
</div>
</div>
</body>
</html>