[Positioning] Measurement: test avg. computation

This commit pass finally all unit tests without any warning!

Measurement:
- Finish unit test (test the average SS).
- Fix update_average_ss() and add_ss().
- average_ss is now double.

owlps-positioning/TODO

@@ -11,9 +11,6 @@
    owlps-positioning/tests/include
    owlps-positioning/doc (générée par doxygen)
 
-- Measurement
-   Vérifier le calcul de moyenne (a priori OK).
-
 - Revoir le diagramme UML
    ° Associations : devraient êtres représentées par des attributs
    pointeurs.

owlps-positioning/measurement.cc

@@ -48,31 +48,20 @@ Measurement::~Measurement()
 /* *** Write accessors *** */
 
 
-void Measurement::update_average_ss()
-{
-  average_ss = 0 ;
-
-  for (vector<int>::const_iterator i = ss_list.begin() ;
-       i != ss_list.end() ; ++i)
-    {
-      float ss_mwatts =
-        pow(10, (float) *i / 10.0) +
-        (ss_list.size() * pow(10, average_ss / 10.0)) ;
-      average_ss = 10 * log10(ss_mwatts / ss_list.size()) ;
-    }
-}
-
-
 /**
  * #average_ss is updated to include the new value.
+ * @param ss_dbm The signal strength to add to #ss_list (in dBm).
  */
-void Measurement::add_ss(const int &ss)
+void Measurement::add_ss(const int &ss_dbm)
 {
-  float ss_mwatts =
-    pow(10, (float) ss / 10.0) +
-    (ss_list.size() * pow(10, average_ss / 10.0)) ;
-  ss_list.push_back(ss) ;
-  average_ss = 10 * log10(ss_mwatts / ss_list.size()) ;
+  double total_ss_mwatts =
+    pow(10, static_cast<double>(ss_dbm) / 10.0) + // New SS in mW
+    (ss_list.size() * pow(10, average_ss / 10.0)) ; // Other values in mW
+
+  ss_list.push_back(ss_dbm) ; // Add new value (dBm)
+
+  // Update average converting back in dBm
+  average_ss = 10.0 * log10(total_ss_mwatts / ss_list.size()) ;
 }
 
 
@@ -101,6 +90,30 @@ void Measurement::clear()
 
 
 
+/* *** Operations *** */
+
+
+void Measurement::update_average_ss()
+{
+  if (ss_list.size() == 0)
+    {
+      average_ss = 0 ;
+      return ;
+    }
+
+  double total_ss_mwatts = 0 ;
+
+  for (vector<int>::const_iterator i = ss_list.begin() ;
+       i != ss_list.end() ; ++i)
+    // Add the current value in mW to the total
+    total_ss_mwatts += pow(10, static_cast<double>(*i) / 10.0) ;
+
+  // Compute the average in mW and convert it to dBm
+  average_ss = 10 * log10(total_ss_mwatts / ss_list.size()) ;
+}
+
+
+
 /* *** Operators *** */
 
 

owlps-positioning/measurement.hh

@@ -13,13 +13,17 @@ class Measurement
 protected:
   /// The AccessPoint that performed the measurement
   AccessPoint *ap ;
-  /// List of signal strengths captured
+  /// List of signal strengths captured (in dBm)
   std::vector<int> ss_list ;
-  /// Average of all signal strength captured
-  float average_ss ;
+  /// Average of all signal strength captured (dBm)
+  double average_ss ;
 
+  /** @name Operations */
+  //@{
   /// Recalculates #average_ss from #ss_list
   void update_average_ss(void) ;
+  //@}
+
 
 public:
   /// Constructs a Measurement from an AccessPoint (or default constructor)
@@ -40,7 +44,7 @@ public:
   /// #ss_list read accessor
   const std::vector<int>& get_ss_list() const ;
   /// #average_ss read accessor
-  float get_average_ss() const ;
+  double get_average_ss() const ;
   //float get_ss_square_distance(const float &ss) const ;
   //@}
 
@@ -49,7 +53,7 @@ public:
   /// #ap write accessor
   void set_ap(const AccessPoint *_ap) ;
   /// Adds a signal strength to #ss_list
-  void add_ss(const int &ss) ;
+  void add_ss(const int &ss_dbm) ;
   /// #ss_list write accessor
   void set_ss_list(const std::vector<int> &_ss_list) ;
   /// Reinitialises the Measurement
@@ -85,7 +89,7 @@ inline const std::vector<int>& Measurement::get_ss_list() const
 }
 
 
-inline float Measurement::get_average_ss() const
+inline double Measurement::get_average_ss() const
 {
   return average_ss ;
 }
@@ -98,7 +102,7 @@ inline float Measurement::get_average_ss() const
 
 
 
-/* *** write accessors *** */
+/* *** Write accessors *** */
 
 
 inline void Measurement::set_ap(const AccessPoint *_ap)

owlps-positioning/tests/measurement_test.hh

@@ -44,14 +44,32 @@ public:
     vi1.push_back(-78) ;
     vi1.push_back(-21) ;
     TS_ASSERT_EQUALS(m1.get_ss_list(), vi1) ;
-    TS_WARN("TODO: Test average SS.") ;
 
+    /* *** Average computation ***
+     *
+     * We need to convert all dBm values into mW, compute the average
+     * and convert mW back to dBm.
+     * (1) P[mW] = 10^(P[dBm] / 10)
+     * (2) P[dBm] = 10 log10(P[mW])
+     *
+     * So for the dBm values -33, -78, -21, we have:
+     * -33 dBm = 10^(-33/10) mW = 0.0005012 mW
+     * -78 dBm = 10^(-78/10) mW = 0.00000001585 mW
+     * -21 dBm = 10^(-21/10) mW = 0.0079433 mW
+     * And:
+     * ( 10^(-33/10) + 10^(-78/10) + 10^(-21/10) ) / 3 = 0.0028148 mW
+     * Back to dBm:
+     * 0.0028148 mW = -25.505481 dBm
+     */
+    TS_ASSERT_DELTA(m1.get_average_ss(), -25.505481, 0.0001) ;
+
+    m1.clear() ;
     std::vector<int> vi2 ;
-    vi1.push_back(-54) ;
-    vi1.push_back(-1) ;
+    vi2.push_back(-54) ;
+    vi2.push_back(-1) ;
     m1.set_ss_list(vi2) ;
     TS_ASSERT_EQUALS(m1.get_ss_list(), vi2) ;
-    TS_WARN("TODO: Test average SS.") ;
+    TS_ASSERT_DELTA(m1.get_average_ss(), -4.0102782, 0.0001) ;
 
     m1.clear() ;
     Measurement m2 ;