Author Topic: Different altitude values  (Read 1190 times)


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Different altitude values
« on: October 26, 2015, 21:09:41 »
Hi menion,
I saw this every time during my holidays in alps (with much more elevation :D ... and difference  :()

But yesterday I found the time to check the different values:
- when I planned the route I've got the values 152m down and 153 up
- at the end of the tour just before saving I had 180m down and 210 upd
- after saving the values where 138 down and 147 up

In settings I have altitude correctur disabled (because I want to use the build in barometer which hard worked fine with orux).
While writing I just saw another setting "GPS altitude optimize" which is set to "on".

My question or lack of understanding:
- when is what method of altitude measure used ?
- can I set settings to only one method in all cases ? (maybe the most accurate  ::))

Offline poutnikl

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Re: Different altitude values
« Reply #1 on: October 27, 2015, 16:02:36 »
There are up to 3 sources of data. SRTM radar data, GPS data and altimeter data.

During planning,  heights are used from Locus elevation SRTM DB ( Space-shuttle Radar Topography Mission )

During track recording, they are taken either from current GPS data, either from pressure altimeter.

Altitude correction is the correction of WGS84 Earth geoid model to real Earth. For the middle Europe, the raw GPS height is about 60 metres higher than real one.

Optimize GPS altitude explicitly states it uses offline elevation data, i.e. SRTM radar dat. As altimeter is much more precise than GPS, especially for relative and short term values, you should consider to turn it OFF.