Originally Posted by
tenrec
If that's the case, I wonder if the accuracy would vary on different days as the barometric pressure varies. I also wonder if any apps or devices use topographical maps along with GPS data -- I expect that would be significantly more accurate.
The Garmin Connect website (connect.garmin.com) has an "elevations correction" feature you can use after the fact to correct the errors in recorded elevation data.
From my most recent ride (82.23 mi), elevation gain:
Without elevation corrections (barometric elevation): 6,726 ft
With elevation corrections (elevation from "professional surveys"): 8,089 ft
It's hard to know which of these is "correct". I was riding in hilly terrain, so any GPS inaccuracies could have put me up a steep slope or down a ravine.
I trust the barometric data more than these "professional surveys" corrections, and both of them over any GPS elevation data.