         return envelope
     }
     
-    /** Returns a ShapeKitPolygon that represents the bounding envelope of this geometry. */
+    /** TODO: missing description */
     func pointOnSurface() -> Point {
         let pointOnSurfaceGEOM = GEOSPointOnSurface_r(GEOS_HANDLE, self.geometry)
         let pointOnSurface = Geometry.create(pointOnSurfaceGEOM, destroyOnDeinit: true) as! Point

        return boundary
    }
    
    /** Returns a ShapeKitPoint representing the geometric center of the geometry. The point is not guaranteed to be on the interior of the geometry. */
    func centroid() -> Point {
        let centroidGEOM = GEOSGetCentroid_r(GEOS_HANDLE, self.geometry)
        let centroid = Geometry.create(centroidGEOM, destroyOnDeinit: true) as! Point
        return centroid
    }
    
    /** Returns the smallest ShapeKitPolygon that contains all the points in the geometry.
    */
    func convexHull() -> Polygon {
        let convexHullGEOM = GEOSConvexHull_r(GEOS_HANDLE, self.geometry)

        return convexHull
    }
    
    /** Returns a Polygon that represents the bounding envelope of this geometry.
    */
    func envelope() -> Polygon {
        let envelopeGEOM = GEOSEnvelope_r(GEOS_HANDLE, self.geometry)
