https://learn.microsoft.com/en-us/uwp/api/windows.devices.geolocation.geopoint.altitudereferencesystem?view=winrt-28000
Geopoint.AltitudeReferenceSystem Property (Windows.Devices.Geolocation) - Windows apps | Microsoft...
The altitude reference system of the geographic point. GeoPoint will default to a value of unspecified when constructed without an altitude reference system....
windows devicesgeopointpropertygeolocationapps