diff --git a/owlps-positioning/src/point3d.cc b/owlps-positioning/src/point3d.cc
index 31f0899..9012975 100644
--- a/owlps-positioning/src/point3d.cc
+++ b/owlps-positioning/src/point3d.cc
@@ -24,9 +24,9 @@ float Point3D::square_distance(const Point3D &source) const
  * The distance is not square rooted after the computation, in order
  * to optimise comparisons.
  */
-float Point3D::square_distance(const float &_x,
-                               const float &_y,
-                               const float &_z) const
+float Point3D::square_distance(const float _x,
+                               const float _y,
+                               const float _z) const
 {
   return
     (x - _x) * (x - _x) +
diff --git a/owlps-positioning/src/point3d.hh b/owlps-positioning/src/point3d.hh
index ef63bd9..0e39826 100644
--- a/owlps-positioning/src/point3d.hh
+++ b/owlps-positioning/src/point3d.hh
@@ -13,7 +13,7 @@ protected:
   float z ; ///< Vertical coordinate
 
 public:
-  Point3D(const float &_x = 0, const float &_y = 0, const float &_z = 0):
+  Point3D(const float _x = 0, const float _y = 0, const float _z = 0):
     x(_x), y(_y), z(_z) {}
 
   Point3D(const Point3D &source):
@@ -33,10 +33,10 @@ public:
 
   /** @name Write accessors */
   //@{
-  void set_x(const float &_x) ;
-  void set_y(const float &_y) ;
-  void set_z(const float &_z) ;
-  /// Sets all coordinates
+  void set_x(const float _x) ;
+  void set_y(const float _y) ;
+  void set_z(const float _z) ;
+  void set_coordinates(const float _x, const float _y, const float _z) ;
   void set_coordinates(const Point3D &source) ;
   //@}
 
@@ -47,13 +47,16 @@ public:
   /// Euclidean distance to a Point3D
   float distance(const Point3D &p) const ;
   /// Square euclidean distance to a 3-float defined point
-  float square_distance(const float &mx,
-                        const float &my,
-                        const float &mz) const ;
+  float square_distance(const float mx,
+                        const float my,
+                        const float mz) const ;
   /// Euclidean distance to a 3-float defined point
-  float distance(const float &mx,
-                 const float &my,
-                 const float &mz) const ;
+  float distance(const float mx,
+                 const float my,
+                 const float mz) const ;
+  /// Euclidean distance to the radius of a sphere
+  float distance_to_sphere(const Point3D &centre,
+                           const float radius) const ;
   //@}
 
   /** @name Operators */
@@ -99,24 +102,33 @@ inline float Point3D::get_z() const
 /* *** Write accessors *** */
 
 
-inline void Point3D::set_x(const float &_x)
+inline void Point3D::set_x(const float _x)
 {
   x = _x ;
 }
 
 
-inline void Point3D::set_y(const float &_y)
+inline void Point3D::set_y(const float _y)
 {
   y = _y ;
 }
 
 
-inline void Point3D::set_z(const float &_z)
+inline void Point3D::set_z(const float _z)
 {
   z = _z ;
 }
 
 
+inline void Point3D::
+set_coordinates(const float _x, const float _y, const float _z)
+{
+  x = _x ;
+  y = _y ;
+  z = _z ;
+}
+
+
 /**
  * Updates x, y, z by passing a Point3D.
  * This is useful for derivated classes, and different than a direct
@@ -146,14 +158,25 @@ inline float Point3D::distance(const Point3D &source) const
  * Note: to compare distances, use preferably square_distance(),
  * which is more efficient.
  */
-inline float Point3D::distance(const float &_x,
-                               const float &_y,
-                               const float &_z) const
+inline float Point3D::distance(const float _x,
+                               const float _y,
+                               const float _z) const
 {
   return sqrt(square_distance(_x, _y, _z)) ;
 }
 
 
+/**
+ * @param centre The centre of the sphere.
+ * @param radius The radius of the sphere.
+ */
+inline float Point3D::distance_to_sphere(
+  const Point3D &centre, const float radius) const
+{
+  return distance(centre) - radius ;
+}
+
+
 
 /* *** Operators *** */