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Open-water swim distance differs from the track recorded? (Todays swimrun 352m vs. approx 750m, unacceptable)


Did my first open-water swim today with 955. Track looks nice and smooth, but the distance is something that makes me think.

Garmin Connect reports 3810m: 

Opened the GPX in GPXSee as wanted to have a little bit closed look and it looked like it's 4k. Umm. Upload GPX to some online tool:

What are others seeing as open-water swim distance? Does it differ from the GPX track? 

Does anyone have any ideas/explanations to give?

Here is the exported GPX if someone wants to analyze it.

EDIT: Apparently this was just a mild issue compared to todays one. Link to it: 

  • Same story here.

    Track nice and smooth

    Distance point A to point B measured while swimming = ~40m (strait line)

    Distance point A to point B measured on the shore = 60m (strait line parallel to swimming route)

    I guess it has something to do with the swim distance algorithm.

    On a closer look, i imported the same activity, in Golden Cheetah in .fit format and in .gpx format

    The .fit was 326m

    The .gpx was 415m which i think is closer to the truth.

  • Yes of course,  the algorithm works only for @, Garmin has developed open water swim activity only for him, very lucky person! Smile 

  • Yes, so it seems to somehow smooth the swimming distance even more than the track, to the point that the swimming distance seems too little to the reality.

    Now I looked my last swim with 945, it was GC 2043m and GPX track 2.09 km. So much lower difference. So lower that I've not really realized that it's doing that, until now with 955.

    Difference was more noticeable. My friend got 4,1 km from the swim and I even did extra swim compared to her and got just that 3810m. Dunno what watch she has and the track looks more rugged, so probably she has too much distance for the reality.

  • Oh, FFS. First swim run and this is utter nonsense. Like one swim is in Garmin's opinion like 352m, when in Google maps it's around 750m. The percentage this is wrong is just unacceptable.

    Garmin Connect 

    Google maps:

  • Yeah, something is off... My watch needs 40-60 seconds to start showing the correct tempo = distance is not measured correctly. It also is very apparent when changing course. With a 180 tempo goes down to 0 for some seconds.

    I had some of this on my previous 945 but not all this much. You can see it clearly in the graph and also very noticeable with my Forms Swim goggles.

  • Also. I tried swimming from the ladder on the wharf(?) straight out to the first boey and then back, without stopping. Way out was 74 meters and back 58. So big difference.

  • And those are pretty different what can be found from the GPX.

    GPX (speed, not pace, but...):

    GPX has some extra spike on in the end that creates extra meters, but more closer still to reality than the Garmin's distance.

  • Glad to read this. I was wondering why my open water pace suddenly dropped by 30s/100m after getting a new watch. And I know the old one is correct because it was timed in official races.

  • Don't worry, there will be someone that will tell that Garmin doesn't like your style, your pace is slower in open water swim, that it hasn't any problem... i'm hearing this jingle since years. I've done the same "experiment" with google maps, Strava, other sportwatches, reported everything to beta teams for about 4 devices for years... no way. I simply use other brand for my OWS.