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/Curve.js

@@ -52,5 +52,41 @@ OpenLayers.Geometry.Curve = OpenLayers.Class(OpenLayers.Geometry.MultiPoint, {
         return length;
     },
 
+    /**
+     * APIMethod: getGeodesicLength
+     * Calculate the approximate length of the geometry were it projected onto
+     *     the earth.
+     *
+     * projection - {<OpenLayers.Projection>} The spatial reference system
+     *     for the geometry coordinates.  If not provided, Geographic/WGS84 is
+     *     assumed.
+     * 
+     * Returns:
+     * {Float} The appoximate geodesic length of the geometry in meters.
+     */
+    getGeodesicLength: function(projection) {
+        var geom = this;  // so we can work with a clone if needed
+        if(projection) {
+            var gg = new OpenLayers.Projection("EPSG:4326");
+            if(!gg.equals(projection)) {
+                geom = this.clone().transform(projection, gg);
+            }
+        }
+        var length = 0.0;
+        if(geom.components && (geom.components.length > 1)) {
+            var p1, p2;
+            for(var i=1, len=geom.components.length; i<len; i++) {
+                p1 = geom.components[i-1];
+                p2 = geom.components[i];
+                // this returns km and requires lon/lat properties
+                length += OpenLayers.Util.distVincenty(
+                    {lon: p1.x, lat: p1.y}, {lon: p2.x, lat: p2.y}
+                );
+            }
+        }
+        // convert to m
+        return length * 1000;
+    },
+
     CLASS_NAME: "OpenLayers.Geometry.Curve"
 });