Issue
I did a comparison of the Fenix 7 with my TomTom Adventurer during open water swimming. It appeared that the distance logged by the Fenix (on the watch as well on Garmin Connect) was 2231 m whereas the distance logged by the TomTom was 3.16 km. I know from experience that the TomTom is right, hence the Fenix logged distance is to far to short (29% to short!!).
The speed recorded by the Fenix appears 2.37 min/100m which is 2.3 km/h which is also to low since I swim about 3.2 km/h. Makes sense, since the speed is derived from the distance.
Note that I attached both watches to my swimming buoy (20 cm distance between them) for better satellite signal reception. They were above water all the time with a clear 180/360 degree sky view.
Software version: 8.18
Analysis
Exporting both files to GPX (using own software tools) and showing the activities in Oziexporer reveals some remarkable issues
In red the TomTom, in blue the Fenix.
Issues:
- Some parts of the track do not contain trackpoints, revealing as straight lines. Especially in the northern part, which is the first part of swim and in the south-west corner.
- Other parts of the track show trackpoints each second, whereas the Setting: Data Recording -> Frequency is set to 'Smart'. Usually it would skip trackpoints
- Based on this, Oziexplorer reports a distance of 3.05 km for the Fenix, which confirms the 2231 m of the Fenix/Garmin Connect is far to low.
I enclose the original FIT file of the activity: tracklog.studioblueplanet.net/2022-05-17-19-43-02.fit
On close analysis the FIT file contains 1053 erronous [lat, lon] coordinates [180, 180]. This cannot be due to poor satellite reception since the watch was on top of the buoy giving it a 180 degrees sky view 360 degrees around (the best you can get).
Note that in the conversion to GPX format, I filtered the [180, 180] coordinates out.
The GPX contains 2448 correct coordinates. Assuming each coordinate represents the same distance and a wrong coordinate is not counted in the total distance, this would mean the total distance calculated is 2448/(2448+1053) * 3.16 km = 2209 m, which is pretty close to the reported 2231 m by the Fenix and Garmin Connect.
I checked another Open water Swimming activity in which I compared the TomTom (on buoy) and Fenix 7 (on wrist).
TomTom (blue): 2.17 km
Fenix (red): 2.06 km, 17 malformed [180, 180] lat/lon coordinates
I checked a trail run: 1 malformed [180, 180] coordinate
I checked a generic cycling event: 0 malformed coordinates
I checked a short hike: 1 malformed coordinate
Conclusion
- The Fenix logs wrong coordinates [180, 180] in all activities.
In Open Water Swimming they appear to be numerous. - Calculation suggests that this results in wrong distance calculations on the Fenix, which renders the watch not very usable for the serious sporter!!
Other posts on this forum also report wrong total distance for other activities.
Advice:
- Solve the bugs so coordinates are correctly logged
- Make sure that if occasionally a wrong coordinate occurs, it is omitted for distance calculation. In other words calculate the distance only by calculating the distance between correct coordinates. This gives better results than current situation.
