Elevation Figures - Garmin onto Strava
Discussion
There are three ways a GPS unit can derive elevation.
1) Via barometric altimeters. My Garmin Edge apparently has one of these. These are very sensitive, but can be affected by weather changes during the ride.
2) Via GPS triangulation. Will have the same degree of (in)accuracy as the X and Y axis, so expect up to 10 meters error.
3) Via map over-lay when uploaded. This relies on the accuracy of the base-map AND the accuracy of the GPS to be correct.
So take your pick from those three, then combine the error-factor for the difference!
Garmin has "elevation error correction" which switches the barometric readings to map over-lay which can produce a wild discrepancy sometimes when activated.
1) Via barometric altimeters. My Garmin Edge apparently has one of these. These are very sensitive, but can be affected by weather changes during the ride.
2) Via GPS triangulation. Will have the same degree of (in)accuracy as the X and Y axis, so expect up to 10 meters error.
3) Via map over-lay when uploaded. This relies on the accuracy of the base-map AND the accuracy of the GPS to be correct.
So take your pick from those three, then combine the error-factor for the difference!
Garmin has "elevation error correction" which switches the barometric readings to map over-lay which can produce a wild discrepancy sometimes when activated.
Triangulation of altitude isn't as accurate as lateral position. Because all the satellites are on one side (above you) the error range is much higher then when they are all around you.
Your Garmin should be using barometric altitude, but Strava seems to apply some smoothing algorithms to the data coming in, my phone based GPS distance gets annoyingly reduced every time! As a MTB'er we zigzag all over the place and these get smoothed out quite a lot.
Your Garmin should be using barometric altitude, but Strava seems to apply some smoothing algorithms to the data coming in, my phone based GPS distance gets annoyingly reduced every time! As a MTB'er we zigzag all over the place and these get smoothed out quite a lot.
I once found the elevation went very wrong on my Garmin on a ride - a descent into a valley and then the climb out had been recorded as flat. So I tried using the elevation correction on the Garmin site and uploading to Strava - that went very wrong! Completely over calculated my amount of ascent for some reason though this was a while ago so not sure if would be the same now.
ndg said:
Triangulation of altitude isn't as accurate as lateral position. Because all the satellites are on one side (above you) the error range is much higher then when they are all around you.
It's a good point, and one I wish I'd made a while back when arguing with someone about this topic in the past! 
okgo said:
Mine is usually fine.
I really wouldn't worry yourself about 300ft of elevation. It's nothing.
Also the calories figs will be totally wrong so ignore those too
Well, yes, 300ft is nothing if you're regularly doing intervals up Alpe d'Huez! But for us mere mortals, we care about such things. Damn right!I really wouldn't worry yourself about 300ft of elevation. It's nothing.
Also the calories figs will be totally wrong so ignore those too
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