[Positioner] Option ss-similarity

The option positioning.ss-similarity introduced in this commit allows to
chose the desired algorithm to compare two measurements. One can chose
between the historical mean euclidean distance algorithm and the new
algorithm using the number of values within the interval
[mean-std.dev.;mean+std.dev.].

owlps-positioner/cfg/owlps-positioner.conf

@@ -93,6 +93,19 @@ csv-file = /tmp/owlps-positioner.log
 #area-start = -2;-2;0
 #area-stop = 20;30;6
 
+# Algorithm to calculate the similarity, in the signal strength space,
+# of two measurements.
+# The following algorithms are implemented:
+#   - mean: The mean of all the packets in the measurement is
+#     computed, then the euclidean distance between the two means is
+#     used.
+#   - interval: The mean Im and the standard deviation Is of the
+#     packets in the measurement I are computed; the closest reference
+#     measurement R is the one with the highest number of packets in
+#     the interval [Im-Is, Im+Is].
+# The default is "mean".
+#ss-similarity = mean
+
 # Smallest possible value for a received signal strength, in dBm. This
 # depends on the sensibility of the APs' Wi-Fi hardware. It is used to
 # compensate for APs that are not in coverage in a given measurement.
@@ -144,7 +157,7 @@ csv-file = /tmp/owlps-positioner.log
 # algorithm and derivated.
 
 # For a given positioning request, average all the calibration requests
-# associated with a reference point before to compute the SS distance.
+# associated with a reference point before to compute the SS similarity.
 # The default is false, i.e. the positioning request is compared
 # directly to each calibration request.
 #average-reference-points = false

owlps-positioner/src/measurement.cc

@@ -7,6 +7,7 @@
 
 #include "measurement.hh"
 #include "posexcept.hh"
+#include "configuration.hh"
 
 #include <iostream>
 #include <sstream>
@@ -124,6 +125,35 @@ void Measurement::clear()
 /* *** Operations *** */
 
 
+float Measurement::similarity(const Measurement &source) const
+{
+  string algorithm(
+    Configuration::string_value("positioning.ss-similarity")) ;
+
+  if (algorithm == "mean")
+    return ss_square_distance(source) ;
+
+  if (algorithm == "interval")
+    {
+      float
+      interval_min = average_dbm - get_std_deviation(),
+      interval_max = average_dbm + get_std_deviation() ;
+
+      // Count the number of SS of source that are within the interval
+      unsigned int nb_values = 0 ;
+      for (map<pkt_id_t, ss_t>::const_iterator ss =
+             source.ss_list.begin() ; ss != source.ss_list.end() ; ++ss)
+        if (interval_min < ss->second && ss->second < interval_max)
+          ++nb_values ;
+
+      return 1 / nb_values ;
+    }
+
+  throw bad_configuration(
+    "Bad SS similarity algorithm name \""+ algorithm +"\"!") ;
+}
+
+
 void Measurement::recalculate_average()
 {
   average_dbm = 0 ;

owlps-positioner/src/measurement.hh

@@ -91,6 +91,8 @@ public:
 
   /** @name Operations */
   //@{
+  /// Computes the similarity with another Measurement in the SS space
+  float similarity(const Measurement &source) const ;
   /// Computes the distance to another Measurement's SS average
   float ss_square_distance(const Measurement &source) const ;
   /// Computes the distance to another SS value (in dBm)

owlps-positioner/src/posutil.cc

@@ -96,7 +96,7 @@ float PosUtil::ss_square_distance(
       unordered_map<string, Measurement>::const_iterator i2 =
         measurements2.find(i1->first) ;
       assert(i2 != measurements2.end()) ;
-      distance += i1->second.ss_square_distance(i2->second) ;
+      distance += i1->second.similarity(i2->second) ;
     }
 
   return distance / measurements1.size() ;

owlps-positioner/src/userinterface.cc

@@ -26,6 +26,7 @@ namespace po = boost::program_options ;
   "/usr/local/etc/owlps/owlps-positioner.conf"
 
 /* Positioning options */
+#define DEFAULT_SS_SIMILARITY "mean"
 #define DEFAULT_MESHING_GRAIN 0.5
 #define DEFAULT_Z_MESHING_GRAIN 1
 #define DEFAULT_SMALLEST_SS -99
@@ -238,6 +239,10 @@ void UserInterface::fill_positioning_options()
   ("positioning.smallest-ss",
    po::value<int>()->default_value(DEFAULT_SMALLEST_SS),
    "Smallest possible value for a received signal strength, in dBm.")
+  ("positioning.ss-similarity",
+   po::value<string>()->default_value(DEFAULT_SS_SIMILARITY),
+   "Algorithm to calculate the similarity, in the signal strength space,"
+   " between two measurements. Allowed: mean, interval.")
   ("positioning.generate-reference-points",
    po::value<bool>()->default_value(false),
    "Generate reference points from the (auto)calibration requests"
@@ -280,7 +285,7 @@ void UserInterface::fill_positioning_options()
    po::value<bool>()->default_value(false),
    "With the NSS algorithm, for a given positioning request, average"
    " all the calibration requests associated with a reference point"
-   " before to compute the SS distance."
+   " before to compute the SS similarity."
    " The default is false, i.e the positioning request is compared"
    " directly to each calibration request.")
   ("positioning.nss.ignore-ap-reference-points",