diff --git a/owlps-positioner/src/point3d.cc b/owlps-positioner/src/point3d.cc
index 256eb0e..db9110e 100644
--- a/owlps-positioner/src/point3d.cc
+++ b/owlps-positioner/src/point3d.cc
@@ -41,6 +41,18 @@ Point3D::Point3D(const string &source)
 /* *** Distance operations *** */
 
 
+/**
+ * The distance is not square rooted after the computation, in order
+ * to optimise comparisons.
+ */
+float Point3D::square_distance_2d(const Point3D &source) const
+{
+  return
+    (x - source.x) * (x - source.x) +
+    (y - source.y) * (y - source.y) ;
+}
+
+
 /**
  * The distance is not square rooted after the computation, in order
  * to optimise comparisons.
diff --git a/owlps-positioner/src/point3d.hh b/owlps-positioner/src/point3d.hh
index a46d761..4972447 100644
--- a/owlps-positioner/src/point3d.hh
+++ b/owlps-positioner/src/point3d.hh
@@ -53,6 +53,8 @@ public:
 
   /** @name Distance & angles operations */
   //@{
+  /// Square euclidean distance to a Point3D, in 2D
+  float square_distance_2d(const Point3D &p) const ;
   /// Square euclidean distance to a Point3D
   float square_distance(const Point3D &p) const ;
   /// Euclidean distance to a Point3D