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Open water swimming


I tried swim in open water. 
I turn on swim in open water activity, after this I see the screen with time and distance. I stay, not swim but distance increases.  I were staying for 3min. but distance increased by 50 meters. What is the reason of such behavior?
If I use running activity and stand still I can see that distance changes but only by 0.04 meters.

I used GPS+GLONASS mode.

  • Where did you have the watch during the 3min? If it went under water and came back up, even once, that can be explained by GPS error after getting the signal again. And even if didn't loss GPS signal, it's still GPS error.

    For the question what is the reason. It's how the technology works. GPS is usually accurate to some meters. So even if your example is on the land and you are standing and it did measure the place every second that's 180 seconds and 50m/180s is 28 cm/1s, which doesn't sound bad error for GPS.

  • And I would guess that there's some algorithm to try to figure out are you moving or not. So that error wouldn't be so big. Something like, if the movement was under X units, let's read that as the same location as previous. Maybe it could also use gyroscope if the device has that and etc...

  • I'm on the land and stand still.

  • it's what happens all the time with all GPS when standing still. You might not be moving but the satellites are. And with that movement is an error that adds up over time to a distance. 

  • If I turn the running activity on, and stand still, the distance don't change, or change by only 0.04 meters.

  • GPS drift for example.

    change by only 0.04 meters

    I think you mean 40m (0.04km) which is not far off what you say you see with the swimming activity loaded. Remember, swimming shows you metres, running shows you kilometres.

  • It works to put the watch under your swim cap (except for backstroke). I also sometimes put it in my safety buoy, which has a dry pouch.

    I track as a "walk," then edit it in Garmin Connect to be an "open water swim." You have to edit the total distance manually or it will read as 0 yards, but the distance is reported in the track information (e.g., as miles, multiply by 1760 to get yards).

    It's not perfect. The calorie estimate will not be recomputed, so it's totally wrong. (Could fix manually, if you care.). At least this way you can see my track, distance, and speed after the fact.

  • I should use my old FR10 for this and sell my 550$ 645...….Thinking

  • Is this GPS drift fast with 945? I mean, with Swim2 if I stop during the swim, the drift goes crazy, and it measures something like 0:30 pace per 100m. Having 1-2 short check on the watch, and the distance is completely overinflated. Just to see, if Garmin has the same problem with all of their OW capable watch, or they made a huge bug in swim2?