How to get the area string from a polygon using leaflet.draw

Question

I am trying to get the area measurements of polygons so I can list them in a table to the side of the map, next to the name of the polygon. This is what I have tried with no success:

$("#polygon").on("click", function (){
    createPolygon = new L.Draw.Polygon(map, drawControl.options.polygon);
    createPolygon.enable();
}

var polygon = new L.featureGroup();

map.on('draw:created', function (e) {
    var type = e.layerType,
        layer = e.layer;
    if (type === 'polygon') {
      polygons.addLayer(layer);
    }
    var seeArea = createPolygon._getMeasurementString();
   console.log(seeArea);  //Returns null
}

Any help on this would be appreciated!

Answer 1

You can access the geometry utility library provided with Leaflet.

var area = L.GeometryUtil.geodesicArea(layer.getLatLngs());

In your example, you are trying to access a control itself, which is what the variable createPolygon is assigned to. Instead, you want to take the area of the layer that got drawn.

map.on('draw:created', function (e) {
  var type = e.layerType,
      layer = e.layer;
  if (type === 'polygon') {
    polygons.addLayer(layer);
    var seeArea = L.GeometryUtil.geodesicArea(layer.getLatLngs());
    console.log(seeArea);
  }
}

Once you verify you are getting the area, you can just assign it to the variables that populate the table next to the map.

Note: area will be in squareMeters by default

Answer 2

L.GeometryUtil.geodesicArea(layer.getLatLngs())[0] should get you the area.

But I ended up using leaflet-geoman-free to do the drawing and use turf.js to get the area.

map.pm.enableDraw('Polygon', {
   snappable: true,
   snapDistance: 20,
});

map.on('pm:create', e => {
   const layer = e.layer
   alert(turf.area(layer.toGeoJSON()))
});