[Positioner] Add option positioning.smallest-ss

The smallest possible received SS is not hard coded into PosUtil any
more. The default value is now -99 dBm instead of -98.

owlps-positioner/cfg/owlps-positioner.conf

@@ -91,6 +91,12 @@ csv-file = /tmp/owlps-positioner.log
 #area-start = -2;-2;0
 #area-stop = 20;30;6
 
+# 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.
+# The default value is -99 dBm, which should be fine in most cases.
+#smallest-ss = -99
+
 # Generate reference points from the (auto)calibration requests
 # received.
 #generate-reference-points = false

owlps-positioner/src/posutil.cc

@@ -8,6 +8,7 @@
 #include "posutil.hh"
 #include "posexcept.hh"
 #include "stock.hh"
+#include "configuration.hh"
 #include "measurement.hh"
 
 #include <owlps.h>
@@ -48,7 +49,7 @@ void PosUtil::complete_with_dummy_measurements(
   assert(! measurements2.empty()) ;
 
   Measurement dummy ;
-  dummy.add_ss(1, -98) ; // FIXME: should be the smallest possible value
+  dummy.add_ss(1, Configuration::int_value("positioning.smallest-ss")) ;
 
   for (unordered_map<string, Measurement>::const_iterator i =
          measurements1.begin() ; i != measurements1.end() ; ++i)

owlps-positioner/src/userinterface.cc

@@ -27,6 +27,7 @@ namespace po = boost::program_options ;
 
 /* Positioning options */
 #define DEFAULT_MESHING_GRAIN 0.5
+#define DEFAULT_SMALLEST_SS -99
 
 /* Output options */
 #define DEFAULT_TCPEVAAL_HOST "127.0.0.1"
@@ -233,6 +234,9 @@ void UserInterface::fill_positioning_options()
    po::value<string>(),
    "Coordinates of the last point of the deployment area"
    " (string format: \"X;Y;Z\").")
+  ("positioning.smallest-ss",
+   po::value<int>()->default_value(DEFAULT_SMALLEST_SS),
+   "Smallest possible value for a received signal strength, in dBm.")
   ("positioning.generate-reference-points",
    po::value<bool>()->default_value(false),
    "Generate reference points from the (auto)calibration requests"