Elevation data

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May 2017
11:08am, 3 May 2017
172 posts
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F4rley
Is there a way of extracting the elevation data from the information in my garmin? It imports and shows lovely graphs on here, which is great, but can you pull this data out? I want to use just the profiles from different runs / courses to compare.

Thanks
May 2017
11:12am, 3 May 2017
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larkim
What specific garmin do you have? Some have built in altimeters whereas others don't. If it's got an altimeter then the change in elevation on a run / ride should be properly recorded and trustworthy (though I don't know how it could get base elevation without knowing what the local atmospheric pressure at a base station was on that particular day), whereas the GPS elevation data is "well dodgy" (technical term).

The graphs on Fetch (and Strava) for elevation often default to using map data instead of using the data from your garmin, and that's especially true when the garmin itself doesn't have an altimeter.

In terms of extracting it, what sort of extraction are you looking for? A GPX export would normally include data for lat/long as well as elevation in it, so that might be all you need. Getting this from Garmin Connect would be straightforward.
May 2017
11:45am, 3 May 2017
173 posts
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F4rley
Thanks - good point about the map data, having looked at it a bit more the standard export runs off that instead of whatever is recorded as it isn't included. There is an option on Garmin Connect to 'export original' and that does include the elevation data in .fit format which you can then see (I think).

I've done that and can see the elevation data so it looks like it is being recorded.

What I would like to do is be able to display different profiles on the same chart so I think if you can get that as a data set then you can graph them.
May 2017
11:49am, 3 May 2017
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larkim
Elevation is (nearly always) recorded by garmins, irrespective of whether they've got an altimeter in them. The issue is how accurate it is. GPS elevation data is very unreliable (there's a reason airline pilots use barometric altimeters to tell them how high they are rather than GPS satellites!), so whilst it might be in the FIT files, you might find that it isn't good enough to use.

If you can get Garmin Connect to export GPX files with elevation data in them, this website gpxviz.sisao.de might be useful for displaying them in the way you want?
May 2017
12:36pm, 3 May 2017
174 posts
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F4rley
Very helpful, thanks. I'll have a look.
May 2017
1:08pm, 3 May 2017
1921 posts
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larkim
Just as an experiment I downloaded the FIT files and the GPX files from Garmin Connect for two identical runs I've done recently. I ran the FIT files through a converter to turn them into GPX files so I could upload to the website I mentioned above. Here are the results. What's visible is that there are significant differences between the altitude recorded natively by my non-barometric altimeter Garmin Vivoactive, whereas the updates that Garmin does to correct that data which is shown in the GPX file means the two runs are comparable (colours are a little different, but profile is just about bang on identical, as you'd expect if it was being calculated from a map).

FIT 1


FIT 2


GPX 1


GPX 2
May 2017
1:10pm, 3 May 2017
1922 posts
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larkim
It was also an "out and back" route, so it should be a mirror image (as the GPX files show), whereas the FIT files are clearly not!!

I might have to borrow the wife's watch at some point and do the same experiment with hers as that has an altimeter built in.

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Is there a way of extracting the elevation data from the information in my garmin? It imports and sh...

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