How to calculate geodesic area of polygons on map

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03-16-2020 06:11 AM
rsharma
Occasional Contributor III

Hi i want to calculate area of polygons drawn on map geometry, any arcgis sample will be helpful

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RobertScheitlin__GISP
MVP Esteemed Contributor

Rajni,

  A ring is just an array of coordinate and not an actual geometry class thus the geodesicArea method is failing.

Here is what you need to do instead.

      function calculateArea() {
        var area = 0;
        graphicsLayer.graphics.map(function (grap) {
          area = geometryEngine.geodesicArea(grap.geometry, "hectares");
        });
        console.log(area);
      } //End calculateArea‍‍‍‍‍‍‍

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BenElan
Esri Contributor

Take a look at the measure widget: Measurement in 2D | ArcGIS API for JavaScript 4.14 

Noah-Sager
Esri Regular Contributor

There is also a lot of good information inside the GeometryEngine class:

geometryEngine | ArcGIS API for JavaScript 4.14 

rsharma
Occasional Contributor III

Hi Noah , I m trying to get geometry of all polygons from a map with below code, but doen't get rings area in console.

function calculateArea(){
         graphicsLayer.graphics.map(function(grap){
          var updatedGeometry = webMercatorUtils.webMercatorToGeographic(grap.geometry);
          var rings_for_area = updatedGeometry.rings;
          console.log(rings_for_area);//return all rings
         });
   
     var area = geometryEngine.geodesicArea(rings_for_area, "hectares");
        console.log(area);//doesn't return area
 
      }

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KenBuja
MVP Honored Contributor

You have a scope problem. Since the variable rings_for_area is declared inside the map function, it's not available outside the function. Why aren't you calculating the area of the rings inside the map function and summing that up?

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rsharma
Occasional Contributor III

Hi ken, this time i summed it up but due to this bolded code to calculate area, my whole map stops working. No error in console even. No area consoled even.

 function calculateArea(){
          var rings_for_area=[];
          var k=0;
         graphicsLayer.graphics.map(function(grap){
          var updatedGeometry = webMercatorUtils.webMercatorToGeographic(grap.geometry);
          var rings_area = updatedGeometry.rings;
                  rings_for_area= [];
                  rings_area.forEach(function(ring, i) {
                    rings_for_area=ring;
                     k++;
                 });
         });
        console.log(rings_for_area);
        var area = geometryEngine.geodesicArea(rings_for_area, "hectares");
        console.log(area);
       }//End calculateArea

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rsharma
Occasional Contributor III

Do i need to convert them rings_for_area to  webMercatorUtils.geographicToWebMercator, Ok i have converted it and now it returns 0 area value, even when i have a polygon on map

  function calculateArea(){
          var rings_for_area=[];
          var k=0;
         graphicsLayer.graphics.map(function(grap){
          var updatedGeometry = webMercatorUtils.webMercatorToGeographic(grap.geometry);
          var rings_area = updatedGeometry.rings;
                  rings_for_area= [];
                  rings_area.forEach(function(ring, i) {
                    rings_for_area=ring;
                     k++;
                 });
         });
        console.log(rings_for_area);
        var area = geometryEngine.geodesicArea( webMercatorUtils.geographicToWebMercator(rings_for_area), "hectares");
        console.log(area);
       }//End calculateArea

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KenBuja
MVP Honored Contributor

Since the geodesicArea method looks like it only takes a single polygon, try calculating that for each ring in your forEach loop

function calculateArea(){
  var area = 0;
  graphicsLayer.graphics.map(function(grap){
    var updatedGeometry = webMercatorUtils.webMercatorToGeographic(grap.geometry);
    var rings_area = updatedGeometry.rings;
    rings_area.forEach(function(ring, i) {
      area += geometryEngine.geodesicArea( webMercatorUtils.geographicToWebMercator(ring), "hectares");
    });
  });
  console.log(area);
}//End calculateArea‍‍‍‍‍‍‍‍‍‍‍
rsharma
Occasional Contributor III

Hi ken , i used your code as it is, and it still returns 0. i called it here , do i need to call it somewhere else

function addGraphics(vertices) {
          //const vertices = <?php echo json_encode($map_ring_coordinate);?>;

          const polygon = createGeometry(vertices);
          validSymbol = createSymbol([255, 255, 255, 0.3], "solid", 2, [
            255, 121,5]);
          newDevelopmentGraphic = new Graphic({
            geometry: webMercatorUtils.geographicToWebMercator(polygon),
            symbol: validSymbol,
            attributes: {
              newDevelopment: "new store"
            }
          });
          graphicsLayer.addMany([newDevelopmentGraphic]);
         calculateArea();
      } //End addGraphics

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RobertScheitlin__GISP
MVP Esteemed Contributor

Rajni,

  A ring is just an array of coordinate and not an actual geometry class thus the geodesicArea method is failing.

Here is what you need to do instead.

      function calculateArea() {
        var area = 0;
        graphicsLayer.graphics.map(function (grap) {
          area = geometryEngine.geodesicArea(grap.geometry, "hectares");
        });
        console.log(area);
      } //End calculateArea‍‍‍‍‍‍‍
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