Differentiate between true and pressure altitude

Altitude can have different meanings in aviation. So far all our
altitudes were true altitudes. But now we also require pressure altitude
including a conversion method between the two.

Maniphest Tasks: T223

src/blackmisc/aviation/altitude.cpp

@@ -16,8 +16,7 @@
 #include <Qt>
 #include <QtGlobal>
 
-using BlackMisc::PhysicalQuantities::CLength;
-using BlackMisc::PhysicalQuantities::CLengthUnit;
+using namespace BlackMisc::PhysicalQuantities;
 
 namespace BlackMisc
 {
@@ -62,6 +61,24 @@ namespace BlackMisc
             this->m_datum = MeanSeaLevel;
         }
 
+        void CAltitude::convertToPressureAltitude(const CPressure &seaLevelPressure)
+        {
+            if (m_altitudeType == PressureAltitude) { return; }
+            static const CPressure standardPressure(1013.25, CPressureUnit::mbar());
+            const CPressure delta = (standardPressure - seaLevelPressure);
+            double deltaV = delta.value(CPressureUnit::mbar());
+            deltaV *= 30.0;
+            addValueSameUnit(deltaV);
+            m_altitudeType = PressureAltitude;
+        }
+
+        CAltitude CAltitude::toPressureAltitude(const CPressure &seaLevelPressure) const
+        {
+            CAltitude other(*this);
+            other.convertToPressureAltitude(seaLevelPressure);
+            return other;
+        }
+
         void CAltitude::parseFromString(const QString &value)
         {
             this->parseFromString(value, PhysicalQuantities::CPqString::SeparatorsCLocale);

src/blackmisc/aviation/altitude.h

@@ -21,6 +21,7 @@
 #include "blackmisc/dictionary.h"
 #include "blackmisc/icon.h"
 #include "blackmisc/metaclass.h"
+#include "blackmisc/pq/pressure.h"
 #include "blackmisc/propertyindexvariantmap.h"
 #include "blackmisc/stringutils.h"
 #include "blackmisc/variant.h"
@@ -71,6 +72,13 @@ namespace BlackMisc
                 FlightLevel         //!< Flight level
             };
 
+            //! Altitude type
+            enum AltitudeType
+            {
+                PressureAltitude,   //!< Altitude above the standard datum plane
+                TrueAltitude        //!< Height of the airplane above Mean Sea Level (MSL)
+            };
+
             //! \copydoc BlackMisc::Mixin::String::toQString
             QString convertToQString(bool i18n = false) const;
 
@@ -80,6 +88,9 @@ namespace BlackMisc
             //! Constructor
             CAltitude(double value, ReferenceDatum datum, const PhysicalQuantities::CLengthUnit &unit) : CLength(value, unit), m_datum(datum) {}
 
+            //! Constructor
+            CAltitude(double value, ReferenceDatum datum, AltitudeType type, const PhysicalQuantities::CLengthUnit &unit) : CLength(value, unit), m_datum(datum), m_altitudeType(type) {}
+
             //! Constructor, value as CAltitude::MeanSeaLevel
             CAltitude(double value, const PhysicalQuantities::CLengthUnit &unit) : CLength(value, unit), m_datum(MeanSeaLevel) {}
 
@@ -107,6 +118,15 @@ namespace BlackMisc
             //! Flightlevel to MSL
             void toMeanSeaLevel();
 
+            //! Current altitude type
+            AltitudeType getAltitudeType() const { return m_altitudeType; }
+
+            //! Converts this to pressure altitude. Requires the current barometric pressure at MSL
+            void convertToPressureAltitude(const PhysicalQuantities::CPressure &seaLevelPressure);
+
+            //! Returns the altitude converted to pressure altitude. Requires the current barometric pressure at MSL
+            CAltitude toPressureAltitude(const PhysicalQuantities::CPressure &seaLevelPressure) const;
+
             //! Parse value from string
             void parseFromString(const QString &value);
 
@@ -150,10 +170,12 @@ namespace BlackMisc
 
         private:
             ReferenceDatum m_datum; //!< MSL or AGL?
+            AltitudeType m_altitudeType = TrueAltitude;
 
             BLACK_METACLASS(
                 CAltitude,
-                BLACK_METAMEMBER(datum)
+                BLACK_METAMEMBER(datum),
+                BLACK_METAMEMBER(altitudeType)
             );
         };
     } // ns
@@ -161,5 +183,6 @@ namespace BlackMisc
 
 Q_DECLARE_METATYPE(BlackMisc::Aviation::CAltitude)
 Q_DECLARE_METATYPE(BlackMisc::Aviation::CAltitude::ReferenceDatum)
+Q_DECLARE_METATYPE(BlackMisc::Aviation::CAltitude::AltitudeType)
 
 #endif // guard