Getting mean sea level altitude on Android instead of ellipsoidal elevation

Question

For geospatial purposes I need my Android application to deliver the users current mean sea level elevation.

My first attempt was to use the system's own locationManager. When requesting a location it delivers exactly those properties I have to evaluate - longitude, latitude and altitude. Perfect!


val locationManager = getSystemService(context, LocationManager::class.java) ?: return@launch
val locationListener = LocationListener { location ->
    Text("Lat: ${location.latitude}°")
    Text("Lng: ${location.longitude}°")
    Text("z: ${location.altitude}[m NN]") // This is not [m NN] but metres over WGS84 ellipsoid
    Text("horizontal_accuracy: ${location.accuracy}[m]")
    Text("vertical_accuracy ${location.verticalAccuracyMeters}[m]")
    return@LocationListener
}
val criteria = Criteria()
criteria.powerRequirement = Criteria.POWER_HIGH
criteria.accuracy = Criteria.ACCURACY_FINE
val bestProvider = locationManager.getBestProvider(criteria, true) ?: LocationManager.GPS_PROVIDER
locationManager.requestLocationUpdates(bestProvider, 100L, 0f, locationListener)

But when I had a closer look at my altitude result I noticed that the value was 40 meters higher than I expected. Looking further into the topic I learned that Android's LocationManager delivers ellipsoidal altitudes. So the difference I noticed are geoid undulations. I can't use the data the way it is right now as I need mean sea level altitudes.

I know I could include a EGM model into my application, but those calculations are rather complicated and the model would inflate my applications file size. JavaScript (web browser) applications and iOS applications resolve mean sea level altitudes - Is there any way to achieve this on Android without calculating too much? Is there any parameter I didn't see?

EDIT:

As I said there is the possibility to include an EGM96 model. But this will inflate the app by lots - just for the purpose of getting better elevation data.

https://stackoverflow.com/a/12811478

But this seems like a lot of overhead.

score 1 · Answer 1 · answered May 01 '23 at 10:23

1

Maybe I don't understand the question - but practically all Android devices output NMEA "sentences", the $GPGGA sentence includes both orthometric height and the Geoid separation on which that height is based. Regrettably the geoid separation doesn't quite match the latest geoid models but it's reasonably close. In my case Android Android 10 reports 61 metres, Android 13 reports 60.6 metres, the 2011 published value for that location in Iceland is 66 metres.

answered May 01 '23 at 10:23

Leifur

11
1

1

As it’s currently written, your answer is unclear. Please [edit] to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers [in the help center](/help/how-to-answer). – Community May 02 '23 at 20:15
It's true that it's included in the NMEA strings. I was just wondering why the `Location` class that you get when requesting via `requestLocationUpdates` doesn't include the geoid mean sea level elevation but the ellipsoid altitude instead. Why don't they just include both? It feels weird to parse the NMEA string when there is the alternative of using a nice class for this purpose. – lprend Aug 09 '23 at 12:44

score 0 · Accepted Answer · answered Aug 10 '23 at 12:44

From API level 34+ the Location class will also have the property mslAltitudeMeters. This is what I was looking for. As soon as 34 / Android 14 is getting released it will be possible to simply use requestLocationUpdates() on the LocationManager and easily get Mean Sea Level Altitudes without having to evaluate NMEA strings.

Getting mean sea level altitude on Android instead of ellipsoidal elevation

2 Answers2