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Incorrect OpenWater Swimming total distance and speed

scubajorgen
over 3 years ago

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.
  • 0 over 2 years ago

    Does anyone tried open water swim with 10.33 Alpha? I did and seems that distance is now correct!

  • 0 over 2 years ago

    I did a comparison of the Fenix 7 in OWS mode on the wrist (*** stroking) to a TomTom Adventurer on my buoy. I am used to accurate results of the TomTom so I believe this is a fair reference.

    The result after 10 swims (red is Garmin, blue is TomTom): 

    In column 1 the distance as reported by the Garmin watch/Garmin Connect.
    In column 2 the Garmin activity exported to GPX and loaded in OziExplorer. On the average 1.6% longer. Other activity types are well below 1%
    In column 3 the TomTom logged activity. On the average 5.9% longer.

    I believe  the latter is due to smoothing of the Garmin track. Of course this is necessary because of the large GPS error due to *** stroking in which the watch is underwater about half the time. Not smoothing means a jagged track. This smoothing results in cutting corners, like at 4 and 5: these are buoys which I passed right resp. left, and near the shore.

    I encounter few problems with the Fenix in OWS lately.

  • 0 over 2 years ago

    I finally got so fed up with any lack of ownership and response from Garmin, I just bought the Ultra. 

    The results over my 2300m course are that the Ultra reports 100m less than the 735 (which I always knew was over-reporting) and 200m more than the Fenix 7, which I knew was massively under-reporting and the reason I am on this forum. I actually believe the report of the ultra, which ironically coincides with my friend's Swim2

    Also the Ultra provides much more accurate tracking of laps in a pool - it was spot on this morning, whereas the Fenix rarely managed to record 1000m, sometimes giving as low as 400m.

     So I am going to stick with the Ultra.

    But the negatives to it are:

     - Small font size means you can't actually see the time when swimming, which is just stupid and a waste of screen real estate. Specialised swim apps do not address this

     - Interval alerts are not as discernable and also not specifiable to the second, which is also stupid

     - Worse battery life

    But there are many positives that outweigh these issues, including accurate measurement of what I want to measure, so it isn't a waste of money, unlike the Garmins. A shame really, as I really liked the Fenix.

    Here endeth my posts on this forum, which I am sure @philipshambrook will be glad about.

    Goodbye Garmin.

  • 0 over 2 years ago in reply to DanielR1972

    I am not surprised that you changed brand. Having multi sport watch that has such serious open water issues from the January and there is no involvement and solution a year after problem was reported by many users, clearly indicates that Garmin support and watches are severely lacking functionality in some areas although it is marketed as capable in those areas.

    I am glad competition is better that Garmin in some areas. Sentence about philipshambrook was hilarious Slight smile

  • 0 over 1 year ago in reply to scubajorgen

    Interesting idea. I have to try that.