Adding methods for getting geodesic measures from geometries. Assuming geometries can be transformed into Geographic/WGS84, getGeodesicLength and getGeodesicArea should return reasonable 'on the ground' metrics. Use getLength and getArea for the planar metrics. r=crschmidt (closes #1819)

git-svn-id: http://svn.openlayers.org/trunk/openlayers@9248 dc9f47b5-9b13-0410-9fdd-eb0c1a62fdaf

lib/OpenLayers/Geometry/Polygon.js

@@ -60,6 +60,35 @@ OpenLayers.Geometry.Polygon = OpenLayers.Class(
         return area;
     },
 
+    /** 
+     * APIMethod: getGeodesicArea
+     * Calculate the approximate area of the polygon were it projected onto
+     *     the earth.
+     *
+     * Parameters:
+     * projection - {<OpenLayers.Projection>} The spatial reference system
+     *     for the geometry coordinates.  If not provided, Geographic/WGS84 is
+     *     assumed.
+     * 
+     * Reference:
+     * Robert. G. Chamberlain and William H. Duquette, "Some Algorithms for
+     *     Polygons on a Sphere", JPL Publication 07-03, Jet Propulsion
+     *     Laboratory, Pasadena, CA, June 2007 http://trs-new.jpl.nasa.gov/dspace/handle/2014/40409
+     *
+     * Returns:
+     * {float} The approximate geodesic area of the polygon in square meters.
+     */
+    getGeodesicArea: function(projection) {
+        var area = 0.0;
+        if(this.components && (this.components.length > 0)) {
+            area += Math.abs(this.components[0].getGeodesicArea(projection));
+            for(var i=1, len=this.components.length; i<len; i++) {
+                area -= Math.abs(this.components[i].getGeodesicArea(projection));
+            }
+        }
+        return area;
+    },
+
     /**
      * Method: containsPoint
      * Test if a point is inside a polygon.  Points on a polygon edge are