topic Re: How to calculate geodesic area of polygons on map in ArcGIS JavaScript Maps SDK Questions

How to calculate geodesic area of polygons on map

rsharma — Mon, 16 Mar 2020 13:11:38 GMT

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

Re: How to calculate area of polygons on map

BenElan — Mon, 16 Mar 2020 15:13:43 GMT

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

Re: How to calculate area of polygons on map

Noah-Sager — Mon, 16 Mar 2020 19:11:29 GMT

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

geometryEngine | ArcGIS API for JavaScript 4.14

Re: How to calculate geodesic area of polygons on map

rsharma — Tue, 17 Mar 2020 06:09:54 GMT

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
       }

Re: How to calculate geodesic area of polygons on map

KenBuja — Tue, 17 Mar 2020 14:26:37 GMT

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?

Re: How to calculate geodesic area of polygons on map

rsharma — Wed, 18 Mar 2020 04:05:35 GMT

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.

Re: How to calculate geodesic area of polygons on map

UndralBatsukh — Thu, 19 Mar 2020 22:09:32 GMT

Check out this test app to see how it works. Hopefully, it will point you to a right direction.

-Undral

Re: How to calculate geodesic area of polygons on map

rsharma — Fri, 20 Mar 2020 03:42:06 GMT

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

Re: How to calculate geodesic area of polygons on map

KenBuja — Sat, 11 Dec 2021 19:01:12 GMT

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

Re: How to calculate geodesic area of polygons on map

rsharma — Mon, 23 Mar 2020 09:53:33 GMT

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

Re: How to calculate geodesic area of polygons on map

RobertScheitlin__GISP — Sat, 11 Dec 2021 19:01:15 GMT

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

Re: How to calculate geodesic area of polygons on map

rsharma — Fri, 03 Apr 2020 13:31:26 GMT

Sir I have a query this calculate area fn do not calculate instantly, i have it only calculate when i refresh the page and then its calculates total area from whole graohics. how to calculate area instantly when graphics is dropped on map or drawn on map

//Calculate TOtal hectares of Map Geometry
        function calculateArea() {
        var area = 0;
        graphicsLayer.graphics.map(function (grap) {
          area = geometryEngine.geodesicArea(grap.geometry, "hectares");
        });
        totalAreaHectare=totalAreaHectare+=Math.round(area);
        //console.log(totalAreaHectare);
      } //End calculateArea

      });//End require

I am calling it in

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

and here

function addTempGraphic(evt) {
              if(evt.state === "complete" && evt.tool === 'polygon'){
                evt.graphic.symbol = createSymbol([255, 255, 255, 0.3], "solid", 2, [255, 121, 5]);
                evt.graphic.attributes= {
                   newDevelopment: "new store"
                };
              calculateArea();
              //appear polygon as editable first time when it is created
              sketchViewModel.update(evt.graphic, {tool: "reshape"});
            }

Re: How to calculate geodesic area of polygons on map

RobertScheitlin__GISP — Fri, 03 Apr 2020 15:21:56 GMT

Rajni,

The Geometry engine is a client side class and does calculations instantly. I am not sure when you are storing this area to be able to say that it is not updating with a page refresh but that is likely the issue. If you put a break point in your code then you will see that it is instanly.

Re: How to calculate geodesic area of polygons on map

rsharma — Sat, 04 Apr 2020 05:19:20 GMT

Yes it do calculate instantly, but it do not show instantly on my map div which i add on map , why??

view.ui.add(hectareLabel, "bottom-right");

Re: How to calculate geodesic area of polygons on map

RobertScheitlin__GISP — Sat, 04 Apr 2020 11:52:47 GMT

How are you updating that view ui element?

Re: How to calculate geodesic area of polygons on map

rsharma — Mon, 06 Apr 2020 03:35:05 GMT

view.when(function() {
          // Add the boundary polygon and new loted polygon graphics on view
          const property_vertices = <?php echo json_encode($map_ring_coordinate);?>;
          addGraphics(property_vertices);
          addMarker();

var hectareLabel = domConstruct.toDom("<div class='esri-component esri-widget' role='button' id='hectare' title='hectare'><b>"+totalAreaHectare+" HECTARES</b></div>");

view.ui.add(hectareLabel, "bottom-right");

}

Re: How to calculate geodesic area of polygons on map

RobertScheitlin__GISP — Mon, 06 Apr 2020 11:40:48 GMT

Rajni,

The view when property is only changed when the page is first loaded or refreshed to this explains why it is not updating.

You need to get the id of your div and change the innerHTML property of your div to the updated area when you recalculate it.