Open a trail-running .fit file — elevation and GPS under tree cover
A trail run is where a .fit file’s two ideas of “up” diverge, and where GPS is least trustworthy — both of which change how you should read the numbers.
Open your file
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a .fit file from a watch or bike computer
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Barometric gain, not GPS altitude
Watches with a barometric altimeter compute elevation gain from air pressure, and that is the figure a trail .fit file usually reports for total climb. It is more stable than GPS altitude but drifts with weather, and it is a different measurement from the altitude a mapping website re-derives from a terrain model. So a trail run that says one climbing total in the file and another on a route-planner is not an error in either — they measured different things, one from pressure and one from a map.
GPS gaps are expected under canopy
Dense tree cover and steep valleys block satellites, so a trail file’s GPS track has ragged sections and the odd straight-line jump where the watch lost and regained a fix. Read as sensor failure, that looks alarming; it is ordinary for the environment. The distance may lean on the accelerometer through the gaps, which is why trail distance and a re-measured GPS track rarely agree to the metre.
What you get from this page
This page reads your trail file on your device and shows the elevation and position fields it holds — barometric altitude where present, GPS altitude separately — so you can see which your climbing total came from instead of guessing why two apps disagree.
In the corpus this tool is tested against, 65 activities resolved to this sport. See the full activity-type list for every sport a .fit file can declare, and open any .fit file whatever its sport.