Android Question GPS question : altitude data 1

klaus

Expert
Licensed User
As an answer to to this GPS question : altitude data thread.
As the problem is device and or manufacturer specific, I would do it that way:
Use the GPS NMEA sentence.
If the GGA sentence is available use the altitude from there.
If the GGA sentence is not available use the altitude from the Location in Location_Change.
 

emexes

Well-Known Member
Licensed User
If the GGA sentence is not available use the altitude from the Location in Location_Change.
If DOM85 is up to it, I'd still like to try confirm that the NMEA altitude is different to the Location_Change altitude, and if so: how much different, whether the VDOP indications are any good, and perhaps even why they are different.
 

Syd Wright

Well-Known Member
Licensed User
If I were you, I would use the GPS1_NMEA event as Klaus has (twice) suggested and use the $GPGGA NMEA sentence.
For an overview of NMEA sentences, see: http://aprs.gids.nl/nmea
That way you get the data straight from the GPS receiver and not via the Android OS GPS function.

You should note that in order to get accurate Altitude information you need valid signals from more satellites than with Latitude and Longitude. In my experience you need at least 6 reasonably strong satellite signals.

Also it is important to realize that GPS measurements are time and location related. You may get a good GPS fix at one moment and much poorer results 15 minutes later. It all depends on howmany satellites are "visible" and whether their signals are clear or obscured by buildings, trees, mountains etc.
If you compare the results of 4 different Android devices (as described in your other thread) you should do that at the same moment with all 4 units side by side.
 
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