Calculate area of geometry

danielconrad — Tue, 20 Nov 2012 17:04:10 GMT

Hi,

I need to calculate the area of a geometry whose spatial reference is WGS84. I did not find a geodesicArea method on the GeometryEngine class, so I went to use the calculateArea2D method in the Geometry class. This method says:

"If the spatial reference is a Geographic Coordinate System (WGS84) then the 2D area calculation is defined in angular units".

I want to convert the output of this method to acres, but I am having trouble determining the angular unit of the output. AngularUnit.Code lists 10 different angular units.

Does anyone know what the unit is for the output of the calculateArea2D method?

Thanks

Re: Calculate area of geometry

MarkBaird — Fri, 07 Dec 2012 18:28:34 GMT

I would try to project your geometry into a spatial reference with a managable unit (like metres)

So my polygon below is in WGS84. I project it into web mercator and then I have a more useful area unit

        Polygon polygon = new Polygon();
        polygon.startPath(25, 5.59);
        polygon.lineTo(13.42, 3.92);
        polygon.lineTo(12.3, 23.3);
        polygon.lineTo(38.2, 22.9);
        polygon.closePathWithLine();

        SimpleLineSymbol outline = new SimpleLineSymbol(
            new Color(0, 200, 0), 3, SimpleLineSymbol.Style.DASH_DOT_DOT);
        SimpleFillSymbol symbol = new SimpleFillSymbol(new Color(200, 0, 0, 120), outline);
        Graphic graphic = new Graphic(polygon, symbol);
        graphicsLayer.addGraphic(graphic);

        //web mercator works in meters
        SpatialReference webMercator = SpatialReference.create(3857);

        //project from wgs84 into web mercator
        Polygon newPoly = (Polygon) GeometryEngine.project(polygon, map.getSpatialReference(), webMercator);
        double area = newPoly.calculateArea2D();

        //now you have an easier unit of meature to play with
        System.out.println("Area is " + area + webMercator.getUnit().getName() + " squared");

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Calculate area of geometry

Re: Calculate area of geometry