Add temperature calculation for ISA METAR scenario

Required commit in fgdata branch for ISA METAR scenario

src/Environment/climate.cxx

@@ -99,6 +99,8 @@ void FGClimate::bind()
     _tiedProperties.Tie( "snow-level-m", &_snow_level);
     _tiedProperties.Tie( "wind-speed-mps", &_wind_speed);
     _tiedProperties.Tie( "wind-direction-deg", &_wind_direction);
+
+    _tiedProperties.Tie("is-isa", &_is_isa);
 }
 
 void FGClimate::unbind ()
@@ -214,6 +216,7 @@ void FGClimate::update(double dt)
         // calculate sea level parameters from ground level parameters
         // adapted from metarproperties.cxx
         FGEnvironment dummy;
+        dummy.set_is_isa(_is_isa);
         dummy.set_live_update(false);
         dummy.set_elevation_ft(_gl.elevation_m*SG_METER_TO_FEET);
         dummy.set_dewpoint_degc(_gl.dewpoint);

src/Environment/climate.hxx

@@ -192,6 +192,8 @@ private:
     double _wind_direction = -99999.0;	// wind direction in degrees
 
     char _metar[256] = "";
+
+    bool _is_isa = false;
 };
 
 #endif // _FGCLIMATE_HXX

src/Environment/environment.cxx

@@ -115,25 +115,26 @@ _setup_tables ()
 
 void FGEnvironment::_init()
 {
-    live_update = false;
-    elevation_ft = 0;
-    visibility_m = 32000;
-    temperature_sea_level_degc = 15;
-    temperature_degc = 15;
-    dewpoint_sea_level_degc = 5; // guess
-    dewpoint_degc = 5;
-    pressure_sea_level_inhg = 29.92;
-    pressure_inhg = 29.92;
-    density_slugft3 = 0;
-    turbulence_magnitude_norm = 0;
-    turbulence_rate_hz = 1;
-    wind_from_heading_deg = 0;
-    wind_speed_kt = 0;
-    wind_from_north_fps = 0;
-    wind_from_east_fps = 0;
-    wind_from_down_fps = 0;
-    altitude_half_to_sun_m = 1000;
-    altitude_tropo_top_m = 10000;
+  is_isa = false;
+  live_update = false;
+  elevation_ft = 0;
+  visibility_m = 32000;
+  temperature_sea_level_degc = 15;
+  temperature_degc = 15;
+  dewpoint_sea_level_degc = 5; // guess
+  dewpoint_degc = 5;
+  pressure_sea_level_inhg = 29.92;
+  pressure_inhg = 29.92;
+  density_slugft3 = 0;
+  turbulence_magnitude_norm = 0;
+  turbulence_rate_hz = 1;
+  wind_from_heading_deg = 0;
+  wind_speed_kt = 0;
+  wind_from_north_fps = 0;
+  wind_from_east_fps = 0;
+  wind_from_down_fps = 0;
+  altitude_half_to_sun_m = 1000;
+  altitude_tropo_top_m = 10000;
 #ifdef USING_TABLES
     _setup_tables();
 #endif
@@ -188,6 +189,7 @@ FGEnvironment::copy (const FGEnvironment &env)
     altitude_half_to_sun_m = env.altitude_half_to_sun_m;
     altitude_tropo_top_m = env.altitude_tropo_top_m;
     live_update = env.live_update;
+    is_isa = env.is_isa;
 }
 
 static inline bool
@@ -252,6 +254,11 @@ FGEnvironment::read (const SGPropertyNode * node)
     maybe_copy_value(this, node, "turbulence/rate-hz",
                      &FGEnvironment::set_turbulence_rate_hz);
 
+    const SGPropertyNode* child = node->getNode("atmosphere/is-isa");
+    if (child != 0 && child->hasValue()) {
+        set_is_isa(child->getBoolValue());
+    }
+
     // calculate derived properties here to avoid duplicate expensive computations
     _recalc_ne();
     _recalc_alt_pt();
@@ -480,6 +487,11 @@ FGEnvironment::get_elevation_ft () const
   return elevation_ft;
 }
 
+bool FGEnvironment::get_is_isa() const
+{
+  return is_isa;
+}
+
 void
 FGEnvironment::set_visibility_m (double v)
 {
@@ -641,6 +653,10 @@ FGEnvironment::set_altitude_tropo_top_m (double alt)
   }
 }
 
+void FGEnvironment::set_is_isa(bool isa)
+{
+  is_isa = isa;
+}
 
 void
 FGEnvironment::_recalc_hdgspd ()
@@ -687,15 +703,23 @@ FGEnvironment::_recalc_sl_temperature ()
     return;
   }
 
-// Clamp: temperature of the stratosphere, in degrees C:
-  double t_strato = ISA_def[1].temp - atmodel::freezing;
-  if (temperature_degc < t_strato) temperature_sea_level_degc = t_strato;
-  else temperature_sea_level_degc = 
-      temperature_degc + elevation_ft * atmodel::foot * ISA_def[0].lapse;
+  double temperature_shift = elevation_ft * atmodel::foot * ISA_def[0].lapse;
 
-// Alternative implemenation:
-//  else temperature_sea_level_inhg = T_layer(0., elevation_ft * foot,
-//      pressure_inhg * inHg, temperature_degc + freezing, ISA_def[0].lapse) - freezing;
+  if (is_isa) {
+    // The "International Standard Atmosphere" METAR scenario in use
+    temperature_sea_level_degc = 15.0;
+    temperature_degc = temperature_sea_level_degc - temperature_shift;
+  } else {
+    // Clamp: temperature of the stratosphere, in degrees C:
+    double t_strato = ISA_def[1].temp - atmodel::freezing;
+    temperature_sea_level_degc = temperature_degc < t_strato
+                                     ? t_strato
+                                     : temperature_degc + temperature_shift;
+
+    // Alternative implemenation:
+    //  temperature_sea_level_inhg = T_layer(0., elevation_ft * foot,
+    //      pressure_inhg * inHg, temperature_degc + freezing, ISA_def[0].lapse) - freezing;
+  }
 }
 
 void

src/Environment/environment.hxx

@@ -100,6 +100,8 @@ public:
 
   virtual bool set_live_update(bool live_update);
 
+  virtual void set_is_isa(bool isa);
+  virtual bool get_is_isa() const;
 
   FGEnvironment & interpolate (const FGEnvironment & env2, double fraction, FGEnvironment * result) const;
 private:
@@ -146,6 +148,7 @@ private:
   double wind_from_down_fps;
 
   bool     live_update;
+  bool is_isa;
   simgear::TiedPropertyList _tiedProperties;
 
 };

src/GUI/qml/Environment.qml

@@ -192,6 +192,9 @@ Item {
                             }
                         } else {
                             _config.setArg("metar", _weatherScenarios.metarForItem(index))
+
+                            var isISA = _weatherScenarios.nameForItem(index) == "International Standard Atmosphere";
+                            _config.setProperty("/environment/climate/is-isa", isISA);
                         }
 
                         // either way, set the scenario name since Local-Weather keys off