Geoid correction in exported GPX

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I think geoid correction is alrerady implemented in MyTracks, but outputted GPX 
files are not corrected.
It would be great if users can choose wether to output a corrected GPX or a raw 
one.

Original issue reported on code.google.com by uli.p...@gmail.com on 31 May 2011 at 5:13

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By Geoid do you mean just WGS84, or WMM2010? Right now we only use WMM2010 to 
display and save your bearing, not for the track points. In theory most GPS 
chips should already do WGS84 internally, shouldn't they?

(also notice that I only updated Android itself to WMM2010 in (I think) Froyo, 
so older Android versions will still use WMM2005 which is less precise now)

Original comment by rdama...@google.com on 31 May 2011 at 5:26

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For reference:
http://android.git.kernel.org/?p=platform/frameworks/base.git;a=commit;h=9119caa
144c8eafdba986002003521af3aedfe67

(although I think you probably mean WGS84)

Original comment by rdama...@google.com on 31 May 2011 at 5:30

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Sorry for being imprecise, I actually mean WGS84 altitude (or height) 
correction.
I don't know if other chips does internally the correction (i have a Samsung 
GT-i5500 phone), but if i record a track in a known place, the resultant GPX 
shows an altitude of about 48m more then the real one, that roughly corresponds 
to the geoid correction for my area.

I think other apps (such as GPS test) shows the correct value, I have to go 
outside to check, to be sure.

Original comment by uli.p...@gmail.com on 31 May 2011 at 7:13

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If all you want is altitude correction, then you can probably get better than 
WGS84 (which is itself an approximation), e.g. with this API: 
http://code.google.com/apis/maps/documentation/elevation/

If that's what you're looking for, then this is probably the same as issue 46.

Original comment by rdama...@google.com on 31 May 2011 at 7:24

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I don't think altitude correction provided by that google api could be used in 
the way I mean: I use mytracks to track my paragliding flights (and with the 
lowering of Android phones prices it will surely become a trand), so mine are 
3D tracks and without altitude correction I would take off or land several 
meters above the terrain...
With google api you'd correct the altitude to the ground, wich basically is 
what exporting in kml does, but I need to fix the difference between the 
satellite's spheroid and the Earth's geoid, that's it.

At the moment I'm doing this on the exported gpx file with this gpsbabel 
command:
gpsbabel -i gpx -f filename -x height,wgs84tomsl -o gpx -F corrected_filename

Original comment by uli.p...@gmail.com on 31 May 2011 at 7:39

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First, a disclaimer: please don't use the altitude indicated by My Tracks for 
any procedures :) Afaik ICAO also forbids use of GPS for landing/take off - you 
should be using a properly QNH-calibrated altimeter.

I'll need to do some research on the altitude provided by different phone GPSs 
to see if the correction that applies to your phone can also be applied to 
others, or if some of them already apply it internally. Sandor, can you ask 
around 44 if anyone knows the answer to this question? (probably whoever 
implemented GPS support does)

Original comment by rdama...@google.com on 31 May 2011 at 7:55

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Hehe, don't worry, I always use my barometric variometer, and after all I fly 
by VFR, I don't really need to know exactly my altitude ;)
I use mytracks just to record the flight and boast with my friends :D

I've seen such a "bug" in another tracking software, maybe you could ask the 
developer about it. Here's a reference:
http://www.opentom.org/Talk:TTTracklog#The_Tomtom_height_bug

Original comment by uli.p...@gmail.com on 31 May 2011 at 8:24

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Hello! Bumping this one... 

MyTracks is a really nice app, especially for me that can not afford a 
vario/GPS at the moment. But unfortunately I'm having exactly the same problems 
with my Samsung Galaxy S II as thread starter describes. I live in Norway, and 
also here the tracks are plotted around 50 meters above the actual height, as 
you can see on the attached track (opens in google earth). I hope there will be 
a solution for this some day.

- Even

Original comment by even.rog...@gmail.com on 8 May 2012 at 8:44

Attachments:

• [Skogen 15-04-12.kml](https://storage.googleapis.com/google-code-attachments/mytracks/issue-479/comment-8/Skogen 15-04-12.kml)

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And by the way. I tried with GPS test and that app shows the correct altitude.

Original comment by even.rog...@gmail.com on 11 May 2012 at 5:44

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Hi,

unfortunately, this seems to be still an issue. I use a Samsung Galaxy S4, and 
the GPX-tracks recorded by MyTracks do not have the altitude corrected in any 
way, i.e. all elevation data is about 47m too high.

Any chance this will be fixed?

Original comment by erik.die...@gmail.com on 5 Oct 2014 at 2:13

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This is a known issue in Android:
https://code.google.com/p/android/issues/detail?id=53471#c2

Right now the Android developer docs are out of sync with most Android devices. 
 The docs say that altitude is meters above mean sea level (see the above AOSP 
issue link for when this changed), but devices I've seen return meters above 
WGS84 ellipsoid.  I believe the docs are currently in error and developers are 
responsible for converting from WGS84 to mean sea level, but it would be nice 
to get official guidance from Google.  

(I've been holding off in implementing mean sea level altitude in GPSTest 
(https://play.google.com/store/apps/details?id=com.android.gpstest) because of 
this.)

Original comment by sjbarb...@gmail.com on 6 Oct 2014 at 12:37

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Original comment by jshih@google.com on 13 Oct 2014 at 9:44

• Changed state: WontFix