Incorrect OpenWater Swimming total distance and speed

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.
  • A work-around is following: 

    1. Check the shape of the activity on the map in https://connect.garmin.com or on the app
      If the shape looks pretty decent, proceed
      If the shape looks bad (straight sections, especally corners cut off), you may proceed but the results of this work-around may be not so accurate; however it will be better than the original log.

    2. Export the activity to GPX format
      You can check the GPX by importing it in any software capable of displaying GPX files, for example OziExplorer. Such tools give you a distance value based on the good coordinates.

    3. Import the GPX using the 'import data' of https://connect.garmin.com
      You will get an activity with more adequate distance and speed values.
      Or post the GPX on Strava ;-)

    4. Optionally: throw away the original activity

    Another work-around if you swim with a buoy: define your own swimming activity and log it with the device attached to the buoy (normally logged activity won't be smoothed enough I guess for wrist worn watches during swimming...)

  • So until this is worked out, what are the work-around options that have worked for folks? Recommendations? Manage "optimal settings" + Velcro the watch to our swim caps or backs of our wetsuits? Ignore the issue (after posting & voting) and hope it's resolved in a software update? Use a different device (e.g., apple watch for swim activity?)

  • I use a Suunto 9 Peak, or you can try with a 920XT... 

    You can also add your vote here: forums.garmin.com/.../open-water-swim-activity-under-report-distance

  • I also used the Fenix 7 for OWS. After a first failure, I used my Apple Watch 7 on the other wrist in addition to the Fenix 7. Fenix 7 recorded a complete nonsense track and a distance almost 1000 m too long. The correct path (and Distance) is given by the Apple Watch. Could we expect a fast solution for this wrong recording, hopefully in this summer so we can use the Garmin Fenix 7? Or wait for the new Apple Watch for extreme sports to be presented in September, which could replace the Fenix 7? Considering the response time of Garmin to solve serious problems like this (I'm referring to the problem with wrong recording of distance in pool swimming), it seem one should replace the Fenix 7 with an Apple Watch and sell Fenix 7, although I'm hesitating because of its long lasting battery and reliability in other sports mode (running, biking). At this stage the Fenix 7 is of little use, if at al, to triathlets, which also raise questions to the new Forerunner 955.

    File name Avg HeartRate Avg Cadence Avg Speed Distance Ascent
    2022-06-11-101325-OWS-Apple Watch.fit 118.09 bpm 20.50 rpm 1.80 kph 1.41 k 0.00 m
    2022-06-011_Fenix7_OWS.fit 119.47 bpm 24.66 rpm 3.22 kph 2.60 k 0.00 m

  • Seems to me this incorporates another problem: logging of incorrect positions. I am used to some deviation when I use my TomTom Adventurer on my wrist, but compared to that this is pretty bad. The reason is that under water GPS won't work. Therefore only half of the time the watch receives satellite signal (when arm above water), resulting in more inaccuracy.

    Also straight sections are visible which compares to what I observe.

    • What software did you use for comparing the distances?
    • What distance was reported by the Fenix watch itself or with Garmin Connect
    • What satellite system were chosen: GPS or all systems?
    • Smart logging or every second?
    • What is the software version of the device?
    • Or could you send me the .fit?

    Note: I am just interested, not part of the solution I am afraid...

  • I used the analyzer tool by DC. The distance recorded by Garmin itself was 2596 m! Setting was all GPS systems in 1s recording, but no multi frequency. Fenix 7xs system is the newest. All in all, rather disappointing. 

  • I do, in the dry bag off my swim buoy. Presuming that helps with accuracy? 

  • I agree. This is rubbish. I have now gone back to my 735 for OWS. They should stop advertising this as being able to do OWS - it is mis-selling.

  • I attach the watch to my buoy. But do mind not to log as 'Openwater swimming' but for example 'Other' until they fix the issues. The problem obviously is most prominent in OWS. Probably due to the smoothing algoritms used... 

  • They should stop advertising this as being able to do OWS

    Just because it unfortunately does not work for you does not mean it's broken for everyone. 

    And there's plenty more where this came from.

    www.strava.com/.../7255805126