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Open water distance

2758248
over 1 year ago
I got the 955 to track and map during long open water swims. Got in to trouble a couple of times, notably rounding islands and such. At sea level is not always easy to know tell where you are at…
Yesterday I recorded a 8.9km sea swim. I wanted to see this in google earth, so I exported the activity. The track measures 7.1km. That is a huge difference!
 GPS is Garmin specialty, but google earth is a reference. I’m a bit lost: witch one to believe?
I’ve grown very skeptic of the 955 dynamics. Pool data is easy to verify, and it has proven very unreliable.
  • Can not count strokes accurately
  • Misses laps & turns
  • Pauses recordings randomly
Do I have to doubt open water too? Do anyone has done work to verify open water GPS tracking accuracy?
  • 0 over 1 year ago

    I have done some short distance tests comparing different activities for the same course. Open water is the worse. 

    Just go for a walk around your house. First use "walk". Than use "open water". You will see the difference. It shows less detailed course and much shorter distance for open water track. 

    I think Fenix7 and Epix2 have the same issue.

  • 0 over 1 year ago in reply to 9970217

    I could be wrong, but I believe this is because OW mode uses an algorithm to estimate distance since the signal is obscured by being under water for much of the time. My OW distance error was <4% compared to a watch on my buoy (latter in running mode). I could imagine it may be affected by individual stroke differences and speed. Honestly, if you care and want 100% accuracy, you will likely need to keep the watch on a buoy or in your cap.

  • 0 over 1 year ago in reply to 2758248

    Yes there was. It was swimming down the river :) But it was the longest swim I've done and pretty big discrepancy, but like the 352m vs. 750m was just flat water in swim run gear in that post.

    Consistency is getting better! It's has already mostly gone from solid to liquid :D Swimming in solid water is pretty hard (and then one wants to wait it to be somewhat warmer so that the brain doesn't freeze when putting head into the water). 

  • 0 over 1 year ago in reply to Andy275

    Well, previous watches has managed to master the OWS pretty good. Then it started to be bad when they switched to Sony in 945. At first the pretty horrible, lost everything after XX meters. And about after year later the release they managed to pretty much fix 945.

    So it was kind of disappoint to again have GPS issues with the new watch. Jury is still out has the problem fixed, but based on the OP's problem, it hasn't. 

  • 0 over 1 year ago in reply to jmto
    Yes there is a time where the watch may be underwater, and they probably rely on the accelerometer and some recorded standard data to track distance. But they could easily correct this estimate as it goes, instead of keep adding the error. When I look at the track, there are plenty of accurate recorded GPS points, so no shortage of solid references to adjust the distances and the metrics.
    I wouldn’t mind not getting wrong “estimated” real time distances displayed, and having instead an accurate distance updated when the GPS can add to the tally. That way the error at any given time may be 20-30m max.
    I haven’t seen much swimmers mastering the bend wrist freestyle technique. Reading data, specially across screens, requires mostly to stop. So unlike running, there is not much point in real time dynamics.
    Once we stop and record the activity, the distance and metrics would be pretty accurate. Don’t understand why they persist with the inaccurate calculations.