Part 2: Work towards the option of interpolating between climate tiles by combining all climate related ground level parameters in one structure and calculating the sea level tile from the (not yet interpolated) ground level tile. Read the elevelation of the climate tile from the köppen database image which now contains the climate class in the red channel and the ground elevation in the green channel.

src/Environment/climate.hxx

@@ -41,6 +41,25 @@ class FGLight;
 #define MAX_CLIMATE_CLASSES	32
 
 class FGClimate : public SGSubsystem {
+private:
+    struct _ground_tile {
+        SGGeod pos;
+
+        double elevation_m = 0.0;
+        double temperature = -99999.0;
+        double temperature_mean = -99999.0;
+        double temperature_water = -99999.0;
+        double relative_humidity = -99999.0;
+        double precipitation_annual = -99999.0;
+        double precipitation = -99999.0;
+        bool has_autumn = false;
+
+        double dewpoint = -99999.0;
+        double pressure = 0.0;
+
+    } _ground_tile;
+    using ClimateTile = struct _ground_tile;
+
 public:
     FGClimate();
     virtual ~FGClimate() = default;
@@ -58,22 +77,23 @@ public:
     double get_wetness() { return _wetness; }
     double get_lichen_cover() { return _lichen_cover; }
 
-    double get_relative_humidity_pct() { return _relative_humidity_gl; }
-    double get_relative_humidity_sl_pct() { return _relative_humidity_sl; }
-    double get_pressure_hpa() { return _pressure_gl; }
-    double get_pressure_sl_hpa() { return _pressure_sl; }
-    double get_dewpoint_degc() { return _dewpoint_gl; }
-    double get_dewpoint_sl_degc() { return _dewpoint_sl; }
-    double get_temperature_degc() { return _temperature_gl; }
-    double get_temperature_sl_degc() { return _temperature_sl; }
-    double get_temperature_mean_degc() { return _temperature_mean_gl; }
-    double get_temperature_mean_sl_degc() { return _temperature_mean_sl; }
-    double get_temperature_water_degc() { return _temperature_water; }
-    double get_temperature_seawater_degc() { return _temperature_seawater; }
-    double get_precipitation_month() { return _precipitation; }
+    double get_relative_humidity_pct() { return _gl.relative_humidity; }
+    double get_relative_humidity_sea_level_pct() { return _sl.relative_humidity; }
+    double get_pressure_hpa() { return _gl.pressure; }
+    double get_pressure_sea_leevel_hpa() { return _sl.pressure; }
+    double get_dewpoint_degc() { return _gl.dewpoint; }
+    double get_dewpoint_sl_degc() { return _sl.dewpoint; }
+    double get_temperature_degc() { return _gl.temperature; }
+    double get_temperature_sea_leevel_degc() { return _sl.temperature; }
+    double get_temperature_mean_degc() { return _gl.temperature_mean; }
+    double get_temperature_mean_sea_level_degc() { return _sl.temperature_mean; }
+    double get_temperature_water_degc() { return _gl.temperature_water; }
+    double get_temperature_seawater_degc() { return _sl.temperature_water; }
+    double get_precipitation_month() { return _gl.precipitation; }
+    double get_precipitation_annual() { return _gl.precipitation_annual; }
+
     double get_wind_mps() { return _wind_speed; }
     double get_wind_direction_deg() { return _wind_direction; }
-    double get_precipitation_annual() { return _precipitation_annual; }
 
     bool getEnvironmentUpdate() const { return _environment_adjust; }
     void setEnvironmentUpdate(bool value);
@@ -126,7 +146,6 @@ private:
     SGPropertyNode_ptr _metarSnowLevelNode;
     SGPropertyNode_ptr _positionLatitudeNode;
     SGPropertyNode_ptr _positionLongitudeNode;
-    SGPropertyNode_ptr _ground_elev_node;
 
     osg::ref_ptr<osg::Image> image;
     double _image_width = 0;
@@ -142,7 +161,6 @@ private:
     double _adj_latitude_deg = 0.0;	// viewer lat adjusted for sun lat
     double _adj_longitude_deg = 0.0;	// viewer lat adjusted for sun lon
 
-    double _elevation_m = 0.0;
     double _daytime = 0.0;
     double _day_noon = 1.0;
     double _day_light = 1.0;
@@ -150,9 +168,9 @@ private:
     double _season_transistional = 0.0;
     double _seasons_year = 0.0;
     double _is_autumn = -99999.0;
-    bool _has_autumn = false;
 
-    int _code = 0;			// Köppen-Geiger classicfication
+    // Köppen-Geiger classicfications
+    ClimateTile _tiles[3][3];
 
     // environment
     bool _environment_adjust = false;	// enable automatic adjestments
@@ -164,23 +182,13 @@ private:
     double _lichen_cover = -99999.0;	// 0.0 = none, 1.0 = mossy
 
     // weather
+    int _code = 0;			// Köppen-Geiger classicfication
+    ClimateTile _gl;			// ground level parameters
+
+    ClimateTile _sl;			// sea level parameters
     bool _weather_update = false;	// enable weather updates
-    double _relative_humidity_sl = -99999.0;// 0.0 = dry, 1.0 is fully humid
-    double _relative_humidity_gl = -99999.0;
-    double _pressure_gl = 0.0;		// ground level air pressure in hPa
-    double _pressure_sl = 0.0;		// sea level air pressure in hPa
     double _wind_speed = 0.0;		// wind in meters per second
     double _wind_direction = -99999.0;	// wind direction in degrees
-    double _dewpoint_gl = -99999.0;
-    double _dewpoint_sl = -99999.0;
-    double _temperature_gl = -99999.0;	// ground level temperature in deg. C.
-    double _temperature_sl = -99999.0;	// seal level temperature in deg. C.
-    double _temperature_mean_gl = -99999.0; // mean temperature in deg. C.
-    double _temperature_mean_sl = -99999.0; // mean temperature at sea level
-    double _temperature_water = -99999.0; // mean temperature of water
-    double _temperature_seawater = -99999.0; // mean temperature of sea water
-    double _precipitation = -99999.0; // minimal avg. precipitation in mm/month
-    double _precipitation_annual = -99999.0; // global
 
     char _metar[256] = "";
 };