Adjust altitude based on airport temperature

In newer flight simulators true altitude is affected by the temperature.
In cold weather aircraft will be shown higher than they actually are,
unless we correct for it.

PS: people with older flight sims might be displayed with incorrect
height on the glideslope when this option is enabled.

Author: EvenAR

ILS_Window_Plugin/IWDataTypes.h

@@ -3,6 +3,7 @@
 #include <string>
 #include <vector>
 #include <memory>
+#include <map>
 
 class IWWindow;
 
@@ -11,7 +12,7 @@ struct RGB {
 };
 
 struct IWTargetPosition {
-    int trueAltitude;
+    int pressureCorrectedAltitude;
     double latitude;
     double longitude;
 };
@@ -26,6 +27,7 @@ struct IWRadarTarget {
 
 struct IWLiveData {
     std::vector<IWRadarTarget> radarTargets;
+    std::map<std::string, float> airportTemperatures;
 };
 
 struct IWApproachDefinition {

ILS_Window_Plugin/IWPlugin.cpp

@@ -143,6 +143,7 @@ void IWPlugin::OnTimer(int seconds)
                 aircraftWtc,
                 positionHistory
             });
+            liveData.airportTemperatures = airportTemperatures;
         }
     }
 
@@ -156,6 +157,23 @@ void IWPlugin::OnAirportRunwayActivityChanged()
     SyncWithActiveRunways();
 }
 
+void IWPlugin::OnNewMetarReceived(const char* sStation, const char* sFullMetar)
+{
+    // Extract temperature from METAR to be used for altitude correction
+    std::string station = std::string(sStation);
+    std::string fullMetar = std::string(sFullMetar);
+    std::regex temperatureRegex(R"((M?\d{2})\/(M?\d{2}))");
+    std::smatch temperatureMatch;
+    if (std::regex_search(fullMetar, temperatureMatch, temperatureRegex)) {
+        std::string temperatureString = temperatureMatch[1];
+        bool isNegative = temperatureString[0] == 'M';
+        int temperature = std::stoi(temperatureString.substr(1));
+        if (isNegative) {
+            temperature = -temperature;
+        }
+        airportTemperatures[station] = temperature;
+    }
+}
 
 void IWPlugin::SyncWithActiveRunways()
 {

ILS_Window_Plugin/IWPlugin.h

@@ -22,6 +22,7 @@ class IWPlugin : public EuroScopePlugIn::CPlugIn, IIWWndEventListener {
     IWStyling windowStyling;
     IWBehaviourSettings behaviourSettings;
     std::map<std::string, CRect> savedWindowPositions;
+    std::map<std::string, float> airportTemperatures;
 
     void OpenNewWindow(IWApproachDefinition* approach);
     void SyncWithActiveRunways();
@@ -34,6 +35,7 @@ class IWPlugin : public EuroScopePlugIn::CPlugIn, IIWWndEventListener {
     bool OnCompileCommand(const char* sCommandLine) override;
     void OnTimer(int seconds) override;
     void OnAirportRunwayActivityChanged() override;
+    void OnNewMetarReceived(const char* sStation, const char* sFullMetar) override;
 
     // Events from a window
     void OnWindowClosed(IWWindow* window) override;

ILS_Window_Plugin/IWWindow.cpp

@@ -4,10 +4,11 @@
 
 #define MAX_PROCEDURES 100
 
-#define MENU_ITEM_FLIP                  10000
-#define MENU_ITEM_SHOW_LABELS           10001
-#define MENU_ITEM_PROCEDURES_SEL_START  20000
-#define MENU_ITEM_PROCEDURES_NEW_START  30000
+#define MENU_ITEM_FLIP                      10000
+#define MENU_ITEM_SHOW_LABELS               10001
+#define MENU_ITEM_CORRECT_FOR_TEMPERATURE   10002
+#define MENU_ITEM_PROCEDURES_SEL_START      20000
+#define MENU_ITEM_PROCEDURES_NEW_START      30000
 
 BEGIN_MESSAGE_MAP(IWWindow, CWnd)
     ON_WM_PAINT()
@@ -28,6 +29,7 @@ BEGIN_MESSAGE_MAP(IWWindow, CWnd)
     ON_MESSAGE(WM_EXITSIZEMOVE, &IWWindow::OnExitSizeMove)
     ON_COMMAND_EX(MENU_ITEM_FLIP, &IWWindow::OnMenuOptionSelected)
     ON_COMMAND_EX(MENU_ITEM_SHOW_LABELS, &IWWindow::OnMenuOptionSelected)
+    ON_COMMAND_EX(MENU_ITEM_CORRECT_FOR_TEMPERATURE, &IWWindow::OnMenuOptionSelected)
     ON_COMMAND_RANGE(MENU_ITEM_PROCEDURES_SEL_START, MENU_ITEM_PROCEDURES_SEL_START + MAX_PROCEDURES, &IWWindow::OnProcedureSelected)
     ON_COMMAND_RANGE(MENU_ITEM_PROCEDURES_NEW_START, MENU_ITEM_PROCEDURES_NEW_START + MAX_PROCEDURES, &IWWindow::OnProcedureSelected)
 END_MESSAGE_MAP()
@@ -476,10 +478,18 @@ void IWWindow::OnLButtonDown(UINT nFlags, CPoint point)
 bool IWWindow::CalculateTargetCoordinates(const IWTargetPosition& position, CPoint& ptTopView, CPoint& ptSideView)
 {
     // Calculate position relative to the runway
-    double heightAboveThreshold = position.trueAltitude - selectedApproach.thresholdAltitude;
     double distanceToThreshold = CalculateDistance(position.latitude, position.longitude, selectedApproach.thresholdLatitude, selectedApproach.thresholdLongitude);
     double directionToThreshold = CalculateBearing(position.latitude, position.longitude, selectedApproach.thresholdLatitude, selectedApproach.thresholdLongitude);
     double angleDiff = (selectedApproach.localizerCourse - directionToThreshold) / 180.0 * PI; // anglediff in radians
+    double heightAboveThreshold = position.pressureCorrectedAltitude - selectedApproach.thresholdAltitude;
+
+    if (applyTemperatureCorrection) {
+        // In newer flight simulators true altitude is affected by the temperature.
+        // In cold weather aircraft will be shown higher than they actually are, unless we correct for it.
+        // See: https://forums.flightsimulator.com/t/vatsim-ivao-pilotedge-users-be-aware-of-an-important-bug/426142/468
+        int temperatureCorrection = CalculateTemperatureCorrection(position.pressureCorrectedAltitude, selectedApproach.thresholdAltitude, m_latestLiveData.airportTemperatures[selectedApproach.airport]);
+        heightAboveThreshold -= temperatureCorrection;
+    }
 
     double projectedDistanceFromThreshold = distanceToThreshold * cos(angleDiff);
     double projectedDistanceFromExtendedCenterline = distanceToThreshold * tan(angleDiff);
@@ -559,6 +569,13 @@ double IWWindow::CalculateBearing(double lat1, double lon1, double lat2, double
     return bearing * 180.0 / PI;
 }
 
+double IWWindow::CalculateTemperatureCorrection(int planePressAlt, int airportPressureAlt, double surfTemp) {
+    double isaDeviation = surfTemp - 15;
+
+    // Formula is from here: https://www.pprune.org/tech-log/573002-accurate-temperature-correction-formula.html
+    return ((-isaDeviation / -0.0019812) * std::log(1 + (-0.0019812 * planePressAlt) / (288.15 + -0.0019812 * airportPressureAlt)));
+}
+
 std::string IWWindow::GetActiveApproachName() const
 {
     std::lock_guard<std::mutex> lock(approachDataMutex);
@@ -611,6 +628,11 @@ void IWWindow::CreatePopupMenu(CPoint point)
         MENU_ITEM_SHOW_LABELS,
         _T("Show labels by default")
     );
+    menu.AppendMenu(
+        MF_STRING | (this->applyTemperatureCorrection ? MF_CHECKED : MF_UNCHECKED),
+        MENU_ITEM_CORRECT_FOR_TEMPERATURE,
+        _T("Apply temperature correction")
+    );
     menu.AppendMenu(
         MF_STRING,
         MENU_ITEM_FLIP,
@@ -619,6 +641,7 @@ void IWWindow::CreatePopupMenu(CPoint point)
 
     // Display the menu
     menu.TrackPopupMenu(TPM_LEFTALIGN | TPM_RIGHTBUTTON, point.x, point.y, this);
+    
 }
 
 BOOL IWWindow::OnMenuOptionSelected(UINT nID)
@@ -634,6 +657,11 @@ BOOL IWWindow::OnMenuOptionSelected(UINT nID)
         this->showTagsByDefault = !this->showTagsByDefault;
         Invalidate();
     }
+    else if (nID == MENU_ITEM_CORRECT_FOR_TEMPERATURE)
+    {
+        this->applyTemperatureCorrection = !this->applyTemperatureCorrection;
+        Invalidate();
+    }
     return TRUE;
 }
 

ILS_Window_Plugin/IWWindow.h

@@ -81,6 +81,7 @@ class IWWindow : public CWnd, IWTitleBarEventListener {
 
         double CalculateDistance(double lat1, double lon1, double lat2, double lon2);
         double CalculateBearing(double lat1, double lon1, double lat2, double lon2);
+        double CalculateTemperatureCorrection(int planePressAlt, int airportPressureAlt, double surfTemp);
 
         COLORREF rangeStatusTextColor;
         COLORREF windowBackground;
@@ -99,6 +100,7 @@ class IWWindow : public CWnd, IWTitleBarEventListener {
 
         int approachLength;
         bool leftToRight;
+        bool applyTemperatureCorrection = true;
 
         // Dimentions
         float approachHeightFt;