topic Re: getting geodesic area -ve in ArcGIS JavaScript Maps SDK Questions

getting geodesic area -ve

rsharma — Fri, 22 May 2020 15:20:23 GMT

i am using below function to calculate area every time i add and delete a new polygon, It was working fine, but suddenly, i need to change the third party layer which provides polygon vertices for property and now i receive my area in negative value. so in order to co up with it, I added -ve in front of it,

But when i draw a polygon by hand using sketch view model, then i get area in +ve and my area calculated reduces for below formu;la instead of increasing.

Could anyone help me with this??

      //Calculate TOtal hectares of Map Geometry
        function calculateArea() {
        var area = 0;
        setTimeout(function() {
        graphicsLayer.graphics.map(function (grap) {
          area = area+(-(geometryEngine.geodesicArea(grap.geometry, "hectares")));
        });
        totalAreaHectare=Math.round(area);
         jQuery("#hectare").html('<b>'+totalAreaHectare+' HECTARES</b>');
        }, 500);
      } //End calculateArea

Re: getting geodesic area -ve

KenBuja — Fri, 22 May 2020 15:54:48 GMT

If a polygon is drawn counter clockwise, then the area will be a negative number (they are considered to be holes). You can check this with the isClockwise method

Re: getting geodesic area -ve

rsharma — Fri, 22 May 2020 15:57:14 GMT

Sir i get the vertices of polygon from linz db, how can i draw them counter clockwise

Re: getting geodesic area -ve

KenBuja — Fri, 22 May 2020 16:04:24 GMT

Try using the simplify method of the Geometry Engine

Re: getting geodesic area -ve

rsharma — Fri, 22 May 2020 16:16:39 GMT

I tried it like this, but it stop to display geometry other dom elements on my map

var newvertices=geometryEngine.simplify(vertices);
const polygon = createGeometry(newvertices);

Re: getting geodesic area -ve

KenBuja — Sat, 11 Dec 2021 07:01:18 GMT

Are you just wishing to get the correct area or are you doing other things with those geometries?

Why aren't you working with the geometry itself?

graphicsLayer.graphics.map(function (grap) {
  const simplified = geometryEngine.simplify(grap.geometry);
  ...
}
‍‍‍‍‍

If timing is an issue, you can always work with the asynchronous geometry engine

Re: getting geodesic area -ve

rsharma — Sat, 23 May 2020 01:49:33 GMT

Thanks ken It worked , i just need to calculate exact area