Knowledgebase Simulation: Altitudes

swift uses 4 altitude related values

• Elevation (scenery elevation)
• Scenery altitude, aka true altitude
• Scenery AGL, altitude above ground
• Pressure altitude

FSX/P3D

• SimConnect variables http://msdn.microsoft.com/en-us/library/cc526981.aspx
• SimConnect events http://msdn.microsoft.com/en-us/library/cc526980.aspx
• P3D vars http://www.prepar3d.com/SDKv3/LearningCenter/utilities/variables/simulation_variables.html
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "PLANE ALTITUDE", "Feet")
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "PLANE ALT ABOVE GROUND", "Feet")
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "PRESSURE ALTITUDE", "Meters")
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "GROUND VELOCITY", "Knots")
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "GROUND ALTITUDE", "Feet")
• SimConnect_AddToDataDefinition(hSimConnect, CSimConnectDefinitions::DataOwnAircraft, "SIM ON GROUND", "Bool")

Although documentation says the indicated altitude is send as pressure altitude, changing the QNH (altimeter know) does not have any effect. Also failures have no effect.

QNG: Hg 29,92 (1013,20mbar)

Changing weather to thunderstorms, Hg 29,21 (989,2mbar) Pressure altitude changes from 320 to 1026ft

FSUIPC

• Ground altitude: FSUIPC_Read(0x0020, 4, &groundAltitudeRaw, &dwResult)
• Altitude: FSUIPC_Read(0x0570, 8, &altitudeRaw, &dwResult)
• Pressure altitude: FSUIPC_Read(0x34B0, 8, &pressureAltitudeRaw, &dwResult)

Flightgear

• True altitude from FG property /position/altitude-ft
• Pressure altitude from FG property /instrumentation/altimeter/pressure-alt-ft. When /instrumentation/altimeter/servicable == false, as fallback the true altitude /position/altitude-ft is send.