diff --git a/TODO b/TODO
index 69a02c2..1238451 100644
--- a/TODO
+++ b/TODO
@@ -124,6 +124,9 @@
    ° Find why some CalibrationRequest were not deleted when
    calling Stock::delete_calibration_request() (via
    ReferencePoint::delete_requests()).
+   ° Option z-level-number: the Z coordinate represents the number of
+   the building's level. If unactivated, the topology is used to
+   determine a change of level.
 
 - Refactoring
    ° Split Stock::generate_reference_point() into several functions.
diff --git a/owlps-positioner/cfg/owlps-positioner.conf b/owlps-positioner/cfg/owlps-positioner.conf
index 01869fa..a1080cb 100644
--- a/owlps-positioner/cfg/owlps-positioner.conf
+++ b/owlps-positioner/cfg/owlps-positioner.conf
@@ -87,6 +87,8 @@ csv-file = /tmp/owlps-positioner.log
 # Since MinMax is currently the only multilateration method implemented
 # in OwlPS, you should define these parameters if you use any of the
 # multilateration-based algorithms (InterlinkNetworks, FBCM, FRBHM).
+# With the autocalibration, the Z coordinate is the level's number, not
+# a true coordinate in meters.
 # They are declared as strings (X;Y;Z). Do not quote!
 #area-start = -2;-2;0
 #area-stop = 20;30;6
@@ -106,6 +108,9 @@ csv-file = /tmp/owlps-positioner.log
 # and Y axis.
 #generated-meshing-grain-x = 0.5
 #generated-meshing-grain-y = 0.5
+# The Z option is currently a level number instead of a vertical
+# coordinate in meters.
+#generated-meshing-grain-z = 1
 
 # This option allows the calibration requests sent during the
 # positioning phase to be added to the calibration request's list. They
diff --git a/owlps-positioner/src/stock.cc b/owlps-positioner/src/stock.cc
index 07fd0be..2234299 100644
--- a/owlps-positioner/src/stock.cc
+++ b/owlps-positioner/src/stock.cc
@@ -456,14 +456,15 @@ void Stock::regenerate_reference_points()
     Configuration::float_value("positioning.generated-meshing-grain-x") ;
   float step_y =
     Configuration::float_value("positioning.generated-meshing-grain-y") ;
-  float z = 1 ; // FIXME
+  float step_z =
+    Configuration::float_value("positioning.generated-meshing-grain-z") ;
   for (float x = start.get_x() ; x <= stop.get_x() ; x += step_x)
     for (float y = start.get_y() ; y <= stop.get_y() ; y += step_y)
-      //for (float z = start.get_z() ; z <= stop.get_z() ; z += step_z)
-      {
-        Point3D current_point(x,y,z) ;
-        generate_reference_point(current_point) ;
-      }
+      for (float z = start.get_z() ; z <= stop.get_z() ; z += step_z)
+        {
+          Point3D current_point(x,y,z) ;
+          generate_reference_point(current_point) ;
+        }
 }
 
 
@@ -507,12 +508,16 @@ void Stock::generate_reference_point(const Point3D &point)
   for (unordered_map<string, AccessPoint>::const_iterator
        rx = aps.begin() ; rx != aps.end() ; ++rx)
     {
+      /* Skip the AP if it is not at the good level */
+      const Point3D &rx_coord = rx->second.get_coordinates() ;
+      if (rx_coord.get_z() != point.get_z())
+        continue ;
+
       /* Update the mobile's attributes */
       vmob_gain += rx->second.get_antenna_gain() / aps.size() ;
       vmob_pow += rx->second.get_trx_power() / aps.size() ;
 
       /* Choose the 2 nearest APs in angle */
-      const Point3D &rx_coord = rx->second.get_coordinates() ;
       multimap<double, pair<double,
                unordered_map<string, AccessPoint>::const_iterator> >
                sorted_angles ;
@@ -522,14 +527,20 @@ void Stock::generate_reference_point(const Point3D &point)
           if (ref == rx)
             continue ;
 
+          // Skip the AP if it is not at the same level than the
+          // receiver AP:
+          const Point3D &ref_coord = ref->second.get_coordinates() ;
+          if (ref_coord.get_z() != rx_coord.get_z())
+            continue ;
+
+          // Skip the AP if it is not in coverage with the receiver AP:
           float coverage =
             rx->second.received_calibration_from_ap(ref->second) ;
-          // Skip the AP if it is not in coverage with the receiver AP:
           if (coverage < 1) // Less than 1% coverage is ridiculous!
             continue ;
 
           double angle =
-            rx_coord.angle(point, ref->second.get_coordinates()) ;
+            rx_coord.angle(point, ref_coord) ;
           double weight = angle / coverage ;
           pair<double,
                unordered_map<string, AccessPoint>::const_iterator>
diff --git a/owlps-positioner/src/userinterface.cc b/owlps-positioner/src/userinterface.cc
index c266ab9..1a87a8d 100644
--- a/owlps-positioner/src/userinterface.cc
+++ b/owlps-positioner/src/userinterface.cc
@@ -27,6 +27,7 @@ namespace po = boost::program_options ;
 
 /* Positioning options */
 #define DEFAULT_MESHING_GRAIN 0.5
+#define DEFAULT_Z_MESHING_GRAIN 1
 #define DEFAULT_SMALLEST_SS -99
 
 /* Output options */
@@ -249,6 +250,11 @@ void UserInterface::fill_positioning_options()
    po::value<float>()->default_value(DEFAULT_MESHING_GRAIN),
    "When generating reference points, this distance (in meters) will"
    " separate each point to the next in Y.")
+  ("positioning.generated-meshing-grain-z",
+   po::value<float>()->default_value(DEFAULT_Z_MESHING_GRAIN),
+   "When generating reference points, this parameter represents the"
+   " number of the level. Currently, each increment of Y is a new"
+   " level (full 3-D coordinates are not supported yet).")
   ("positioning.accept-new-calibration-requests",
    po::value<bool>()->default_value(false),
    "Add the calibration requests received during the run-time to"