Add ol.geom.flat.linearRingsArea

src/ol/geom/flatgeom.js

@@ -371,6 +371,31 @@ ol.geom.flat.linearRingPerimeter =
 };
 
 
+/**
+ * @param {Array.<number>} flatCoordinates Flat coordinates.
+ * @param {number} offset Offset.
+ * @param {Array.<number>} ends Ends.
+ * @param {number} stride Stride.
+ * @return {number} Area.
+ */
+ol.geom.flat.linearRingsArea = function(flatCoordinates, offset, ends, stride) {
+  var area = 0;
+  var i, ii;
+  for (i = 0, ii = ends.length; i < ii; ++i) {
+    var end = ends[i];
+    var linearRingArea =
+        ol.geom.flat.linearRingArea(flatCoordinates, offset, end, stride);
+    if (i === 0) {
+      area += linearRingArea;
+    } else {
+      area -= linearRingArea;
+    }
+    offset = end;
+  }
+  return area;
+};
+
+
 /**
  * @param {Array.<number>} flatCoordinates Flat coordinates.
  * @param {number} offset Offset.

test/spec/ol/geom/flatgeom.test.js

@@ -159,6 +159,16 @@ describe('ol.geom.flat', function() {
 
   });
 
+  describe('ol.geom.flat.linearRingsArea', function() {
+
+    it('calculates the area with holes', function() {
+      var area = ol.geom.flat.linearRingsArea(
+          [0, 0, 0, 3, 3, 3, 3, 0, 1, 1, 1, 2, 2, 2, 2, 1], 0, [8, 16], 2);
+      expect(area).to.be(8);
+    });
+
+  });
+
   describe('ol.geom.flat.reverseCoordinates', function() {
 
     describe('with a stride of 2', function() {