fix reported QNH/QFE for current temperature

crates/datis-core/src/station.rs

@@ -164,35 +164,35 @@ fn temperatur_report(weather: &WeatherInfo, spoken: bool) -> String {
     )
 }
 
-fn altimeter_report(weather: &WeatherInfo, spoken: bool) -> String {
+fn altimeter_report(weather: &WeatherInfo, alt: u32, spoken: bool) -> String {
     format!(
         "ALTIMETER {}. {}",
         // inHg, but using 0.02953 instead of 0.0002953 since we don't want to speak the
         // DECIMAL here
-        pronounce_number((weather.pressure_qnh * 0.02953).round(), spoken),
+        pronounce_number((weather.get_qnh(alt) * 0.02953).round(), spoken),
         break_(spoken),
     )
 }
 
-fn hectopascal_report(weather: &WeatherInfo, spoken: bool) -> String {
+fn hectopascal_report(weather: &WeatherInfo, alt: u32, spoken: bool) -> String {
     format!(
         "{} hectopascal. {}",
-        pronounce_number((weather.pressure_qnh / 100.0).round(), spoken), // to hPA
+        pronounce_number((weather.get_qnh(alt) / 100.0).round(), spoken), // to hPA
         break_(spoken),
     )
 }
 
-fn qfe_report(weather: &WeatherInfo, spoken: bool) -> String {
+fn qfe_report(weather: &WeatherInfo, alt: u32, spoken: bool) -> String {
     format!(
         "QFE {} {}or {}. {}",
-        pronounce_number((weather.pressure_qfe * 0.02953).round(), spoken), // to inHg
+        pronounce_number((weather.get_qfe(alt) * 0.02953).round(), spoken), // to inHg
         if spoken {
             // add break to make it easier to mentally process the different numbers
             "<break time=\"500ms\" /> "
         } else {
             ""
         },
-        pronounce_number((weather.pressure_qfe / 100.0).round(), spoken), // to hPA
+        pronounce_number((weather.get_qfe(alt) / 100.0).round(), spoken), // to hPA
         break_(spoken),
     )
 }
@@ -478,11 +478,11 @@ impl Airfield {
         report += &weather_condition_report(weather, alt, spoken);
         report += &visibility_report(weather, alt, spoken);
         report += &temperatur_report(weather, spoken);
-        report += &altimeter_report(weather, spoken);
+        report += &altimeter_report(weather, alt, spoken);
 
         report += &format!("REMARKS. {}", break_(spoken));
-        report += &hectopascal_report(weather, spoken);
-        report += &qfe_report(weather, spoken);
+        report += &hectopascal_report(weather, alt, spoken);
+        report += &qfe_report(weather, alt, spoken);
 
         report += &format!("End information {}.", information_letter);
 
@@ -520,16 +520,16 @@ impl Carrier {
             break_(spoken),
         );
 
+        let alt = 21; // carrier deck alt in m
+
         report += &format!(
             "altimeter {}, {}",
             // inHg, but using 0.02953 instead of 0.0002953 since we don't want to speak the
             // DECIMAL here
-            pronounce_number((weather.pressure_qnh * 0.02953).round(), spoken),
+            pronounce_number((weather.get_qnh(alt) * 0.02953).round(), spoken),
             break_(spoken),
         );
 
-        let alt = 21; // carrier deck alt in m
-
         // Case 1: daytime, ceiling >= 3000ft; visibility distance >= 5nm
         // Case 2: daytime, ceiling >= 1000ft; visibility distance >= 5nm
         // Case 3: nighttime or daytime, ceiling < 1000ft and visibility distance <= 5nm
@@ -611,11 +611,11 @@ impl WeatherTransmitter {
         report += &weather_condition_report(weather, alt, spoken);
         report += &visibility_report(weather, alt, spoken);
         report += &temperatur_report(weather, spoken);
-        report += &altimeter_report(weather, spoken);
+        report += &altimeter_report(weather, alt, spoken);
 
-        report += &format!("REMARKS. {}", break_(spoken));
-        report += &hectopascal_report(weather, spoken);
-        report += &qfe_report(weather, spoken);
+        report += &format!("REMARKS. {}", break_(spoken),);
+        report += &hectopascal_report(weather, alt, spoken);
+        report += &qfe_report(weather, alt, spoken);
 
         report += &format!("End information {}.", information_letter);
 

crates/datis-core/src/weather.rs

@@ -54,6 +54,30 @@ pub struct OldClouds {
 }
 
 impl WeatherInfo {
+    /// Get QNH correct for the current temperature (as far as possible in DCS)
+    pub fn get_qnh(&self, alt: u32) -> f64 {
+        self.pressure_qnh + self.pressure_correction(alt)
+    }
+
+    /// Get QFE correct for the current temperature (as far as possible in DCS)
+    pub fn get_qfe(&self, alt: u32) -> f64 {
+        self.pressure_qfe + self.pressure_correction(alt)
+    }
+
+    fn pressure_correction(&self, alt: u32) -> f64 {
+        let alt = m_to_ft(alt as f64);
+        let angels = alt / 1000.0;
+        // ISA at see level is 16 and not 15 in DCS, see
+        // https://forums.eagle.ru/topic/256057-altitude-qnh-error-bug/
+        let isa_at_alt = 16.0 - 1.98 * angels;
+        let isa_diff = self.temperature - isa_at_alt;
+        let palt_diff = 4.0 * isa_diff * angels;
+
+        // translate alt diff into a QNH diff
+        let qnh_diff = (palt_diff / 27.0) * 100.0;
+        qnh_diff
+    }
+
     /// in m
     pub fn get_visibility(&self, alt: u32) -> Option<u32> {
         let clouds_vis = self.clouds.as_ref().and_then(|c| c.get_visibility(alt));