How does Garmin Edge calculate distance when there is no speed sensor? I would think it just uses GPS data but seems like it's not that simple. Usually the distance in .fit file is the same as the distance calculated by 3rd party services using the exported .gpx file or if I remove speed/distance values from the .fit file using fitfiletools. But recently we had a significant difference in distance on two Garmin devices and I wanted to know which one is correct.
My .fit file has the distance of 36.8 km and if I remove speed/distance from it then the distance using coorditanes is 40.8 km. I thought maybe Garmin does some smoothing but looks like other similar .fit files (where I actually used Garmin Edge 510 for hiking) have almost exactly the same distance calculated by the device and using the coordinates.
Where do I dig to find the answer?
Here is the .fit file in question and the exported .gpx.
