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
2009-04-08 23:12:24 +00:00
parent 5f335f4207
commit 08077f0f42
8 changed files with 250 additions and 44 deletions
@@ -205,6 +205,50 @@ OpenLayers.Geometry.LinearRing = OpenLayers.Class(
        return area;
    },
    
+    /**
+     * APIMethod: getGeodesicArea
+     * Calculate the approximate area of the polygon were it projected onto
+     *     the earth.  Note that this area will be positive if ring is oriented
+     *     clockwise, otherwise it will be negative.
+     *
+     * 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 signed geodesic area of the polygon in square
+     *     meters.
+     */
+    getGeodesicArea: function(projection) {
+        var ring = this;  // so we can work with a clone if needed
+        if(projection) {
+            var gg = new OpenLayers.Projection("EPSG:4326");
+            if(!gg.equals(projection)) {
+                ring = this.clone().transform(projection, gg);
+            }
+        }
+        var area = 0.0;
+        var len = ring.components && ring.components.length;
+        if(len > 2) {
+            var p1, p2;
+            for(var i=0; i<len-1; i++) {
+                p1 = ring.components[i];
+                p2 = ring.components[i+1];
+                area += OpenLayers.Util.rad(p2.x - p1.x) *
+                        (2 + Math.sin(OpenLayers.Util.rad(p1.y)) +
+                        Math.sin(OpenLayers.Util.rad(p2.y)));
+            }
+            area = area * 6378137.0 * 6378137.0 / 2.0;
+        }
+        return area;
+    },
+    
    /**
     * Method: containsPoint
     * Test if a point is inside a linear ring.  For the case where a point