1、GeometryService計算面積和長度（Calculate_Feature_Length_Or_Area）功能實現

本文主要介紹利用GeometryService實現面積和長度的計算。首先看一下實現本功能的主要過程：

接下來就一步步介紹實現本功能的具體步驟和方法：

（本文的代碼來自https://developers.arcgis.com/javascript/jssamples/util_measurepoly.html，本文只是提煉部分核心代碼，講解實現的思路，如需獲取所有代碼，請參考上述鏈接）

1、創建Draw對象

 var tb = new Draw(map);
 tb.on("draw-end", lang.hitch(map, getAreaAndLength));
 tb.activate(Draw.FREEHAND_POLYGON);

2、創建GeomeService對象

var geometryService = new GeometryService("http://sampleserver6.arcgisonline.com/arcgis/rest/services/Utilities/Geometry/GeometryServer");
geometryService.on("areas-and-lengths-complete", outputAreaAndLength);

3、getAreaAndLength方法的實現，注意本方法只有在draw-end事件觸發時才會執行

   　　　　function getAreaAndLength(evtObj) {
              var map = this,
                  geometry = evtObj.geometry;
              map.graphics.clear();

              var graphic = map.graphics.add(new Graphic(geometry, new SimpleFillSymbol()));

              //setup the parameters for the areas and lengths operation
              var areasAndLengthParams = new AreasAndLengthsParameters();
              areasAndLengthParams.lengthUnit = GeometryService.UNIT_FOOT;
              areasAndLengthParams.areaUnit = GeometryService.UNIT_ACRES;
              areasAndLengthParams.calculationType = "geodesic";
              geometryService.simplify([geometry], function (simplifiedGeometries) {
                  areasAndLengthParams.polygons = simplifiedGeometries;
                  geometryService.areasAndLengths(areasAndLengthParams);
              });
          }

4、outputAreaAndLength方法的實現，注意，本方法只有GeomeService對象計算完面積和周長才會觸發

        function outputAreaAndLength(evtObj) {
              var result = evtObj.result;
              console.log(json.stringify(result));
              dom.byId("area").innerHTML = result.areas[0].toFixed(3) + " acres";
              dom.byId("length").innerHTML = result.lengths[0].toFixed(3) + " feet";
          }    

 

下面看一下效果圖：