Calculate PolygonArea for RegionChooser

website/polygon.js

@@ -36,9 +36,9 @@ function Pen(map) {
 				this.drawPolygon(this.listOfDots);
 				$('#dataPanel').empty();
 				$('#dataPanel').append("WGS84 Coordinates<br/>");
-				$('#dataPanel').append(this.getData("WGS84"));
+				$('#dataPanel').append(this.getWGS84Data() + "<br/>\n");
 				$('#dataPanel').append("GSK3 Coordinates<br/>");
-				$('#dataPanel').append(this.getData("GSK3"));
+				$('#dataPanel').append(this.getGSK3DataAndArea());
 			} else {
 				if (null != this.polyline) {
 					this.polyline.remove();
@@ -78,19 +78,36 @@ function Pen(map) {
 	this.getListOfDots = function() {
 		return this.listOfDots;
 	}
-	this.getData = function(referenceSystem) {
+	this.getWGS84Data = function() {
+		if (this.polygon != null) {
+			var data = "";
+			var paths = this.polygon.getPlots();
+			var xs = [];
+			var ys = [];
+			paths.getAt(0).forEach(function(value, index) {
+				data += (value.toString() + "<br/>");
+			});
+			return data;
+		} else {
+			return null;
+		}
+	}
+
+	this.getGSK3DataAndArea = function(referenceSystem) {
 		if (this.polygon != null) {
 			var data = "";
 			var paths = this.polygon.getPlots();
 			var fromProjection = proj4('EPSG:4326');
 			var toProjection = proj4('EPSG:31467');
+			var xs = [];
+			var ys = [];
 			paths.getAt(0).forEach(function(value, index) {
-				if (referenceSystem == "WGS84") {
-					data += (value.toString() + "<br/>");
-				} else if (referenceSystem == "GSK3") {
-					data += "(" + (proj4(fromProjection, toProjection, [ value.lng(), value.lat() ]).toString() + ")<br/>");
-				}
+				var gk3_coords = proj4(fromProjection, toProjection, [ value.lng(), value.lat() ]);
+				xs.push(gk3_coords[0] - 3500000);
+				ys.push(gk3_coords[1] - 5000000);
+				data += "(" + (gk3_coords.toString() + ")<br/>");
 			});
+			data += "<br/>\nArea : " + (Math.round(polygonArea(xs, ys) / 1000) / 10).toString() + " ha<br/>";
 			return data;
 		} else {
 			return null;
@@ -191,4 +208,15 @@ function Polygon(listOfDots, map, pen, color) {
 		});
 	}
 	this.addListener();
-}
\ No newline at end of file
+}
+
+function polygonArea(X, Y, numPoints) {
+	area = 0; // Accumulates area in the loop
+	j = X.length - 1; // The last vertex is the 'previous' one to the first
+
+	for (i = 0; i < X.length; i++) {
+		area = area + (X[j] + X[i]) * (Y[j] - Y[i]);
+		j = i; // j is previous vertex to i
+	}
+	return Math.abs(area / 2);
+}