Question: How Does Garmin Calculate Elevation from Altitude Data in FIT Files?

5320793 1 month ago

Hi all! I’m trying to understand how Garmin calculates elevation for activities, and I’m hoping someone here might be able to help!

I’ve been analyzing the FIT files from my Garmin device and noticed that the files only include altitude data, with no separate elevation field. However, when I look at the same activity on the Garmin dashboard, it shows an elevation value that differs from the raw altitude in the FIT file.

From what I’ve read online, it seems some sources use altitude directly as elevation, but Garmin appears to be calculating elevation differently. Could anyone explain how Garmin determines this elevation value? Does it involve additional data or calculations beyond the raw altitude?

I’ll share an image for comparison between the FIT file’s altitude values and the elevation displayed on Garmin’s dashboard. Thanks in advance for any insights!

Fit File's Altitude

Garmin Dashboard's Elevation

Top Replies

trux 1 month ago +1

Which device is it from? Does it have a barometric altimeter? If not (and I suspect it is the case), then the altitude in the FIT file comes from the GPS, and since the GPS altitude is generally very inaccurate…

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0 trux 1 month ago

Which device is it from? Does it have a barometric altimeter? If not (and I suspect it is the case), then the altitude in the FIT file comes from the GPS, and since the GPS altitude is generally very inaccurate, Garmin Connect replaces the data with the cartographic altitude, instead. It means getting the elevation of every track point from the cartographic data. That's more accurate than using the vertical data directly from the GPS.