[Positioning] Add Stock::ap_matrix_get_ss()

Add double Stock::ap_matrix_get_ss(transmitter, receiver).
This is the first step to handle self-calibration in owlps-positioning.

The idea is to simulates a square matrix of the listeners, with the
transmitters in one dimension and the receivers in the other dimension.
matrix[transmitter][receiver] is the signal strength received by
'receiver' from 'transmitter'.
The purpose of Stock::ap_matrix_get_ss() is precisely to access the
entry matrix[transmitter][receiver].

Note that the access is read-only, as the pseudo-matrix is (or will be)
filled by the standard mechanism of (auto)calibration requests and
measurements stored in Stock.

owlps-positioning/src/stock.cc

@@ -239,6 +239,17 @@ void Stock::update_all_friis_indexes()
 }
 
 
+double Stock::ap_matrix_get_ss(const std::string &mac_transmitter,
+                               const std::string &mac_receiver)
+{
+  const AccessPoint &receiver = get_ap(mac_receiver) ;
+  const ReferencePoint &rp =
+    get_reference_point(receiver.get_coordinates()) ;
+
+  return rp.average_measurements(mac_transmitter) ;
+}
+
+
 
 /* *** ReferencePoint operations *** */
 

owlps-positioning/src/stock.hh

@@ -93,6 +93,8 @@ public:
   static AccessPoint& getw_ap(const std::string &mac) ;
   /// Updates the friis indexes of all the APs
   static void update_all_friis_indexes(void) ;
+  static double ap_matrix_get_ss(const std::string &mac_transmitter,
+                                 const std::string &mac_receiver) ;
   //@}
 
   /** @name ReferencePoint operations */