diff --git a/lib/geometry/Geometry.class.php b/lib/geometry/Geometry.class.php
index df03debd..8807841f 100644
--- a/lib/geometry/Geometry.class.php
+++ b/lib/geometry/Geometry.class.php
@@ -39,6 +39,8 @@ abstract public function getBBox();
   abstract public function asArray();
   abstract public function getPoints();
   abstract public function explode();
+  abstract public function greatCircleLength(); //meters
+  abstract public function haversineLength(); //degrees
 
 
   // Public: Standard -- Common to all geometries