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Tracked distance is too long but gps track is spot on

Hello, 

I've had my 955 for a year or so and never had issues with measured distance. It would always be within the margin of error of the other paddlers around me. 

I just did a 120ish mile canoe race in Michigan last weekend. River snakes through trees but there are also wide open lake areas. I wore the watch on my wrist the while time in SatIQ mode.

The gps track is spot on and matches the gps tracks of 3 other friends I compared it with. No weird data points at all. But the computed distance is 2.5 km longer than anybody else which seems unusual despite the long distance. Last May I did a 70 mile race and did not have that issue.

I've looked through past posts here and on reddit and saw a few comments saying that maybe multiband was causing an issue or something to do with arm motion? But it had never happened like this before.. 

Any ideas what could be the problem? Has the 965 been having that issue too? 

Thank you! 

  • Have you tried analyzing the fit file of that activity? Can you provide this fit file?

  • Here is the fit file. I'm not quite sure how I can analyze it? Thanks!

    ARCM 2023.fit.zip

  • Don't know if they are even options for Canoe activities, but are there options for 3d speed/distance that maybe are on?  I know on running those can screw up the distances.

    Just took your FIT files and when running the distance correction on Strava (which just recalculates the distance based on the GPS points) it went from 115.18 mi to 114.6 mi.

    Were you in the same canoe as those friends?  If so, you could export their GPX files and compare them with yours on something like http://www.mygpsfiles.com/app/

  • When my activity synced with Strava, the total was exactly the same (185.26 km in Garmin Connect and Strava which usually doesn't happen). That would be 115.79 mi. How did you get that 115.18? 114.6 mi would be right on what the actual distance should be but I don't see it anywhere. 

    I did compare my gpx track with multiple friends'. Some variation is expected because we were all in different canoes but the lines all track exactly the same or almost so not enough to account for the large gap in distance). 

    I use the SUP activity profile. I don't remember ever seeing an option for 3d speed/distance. 

  • I don't know where your friends started the activity log. You started the activity already in the parking lot. I am sending the corrected fit file.

    ARCM 2023-fixed.zip

  • Hi! 

    Thanks for your help. 

    We all started from the same spot as the race started with a 400m run to the water hence the track starting in the street Relaxed I had already cleared the extra time from before the start.

    I'll look at the fit file you sent! 

    @Juraj_ What would cause such a difference in distance? My activities in Garmin Connect had always been right on point until this one (and I have paddled in similar conditions before). 

  • @ psychoswim

    Please set your activity recording to be performed every second. You had smart recording set up and then there are bigger errors in the speed and distance recording.

  • It might be a stupid question.. Why would the actual gps track look right on with no errors if the problem is smart recording? 

    Thank you for your suggestions.

  • https://support.garmin.com/en-US/?faq=s4w6kZmbmK0P6l20SgpW28

    roughly translated into more precise recording of your track.

  • Thank you. I had seen that page before. It says smart recording does not really affect the gps track but that it impacts battery life and storage. What would be the impact on battery life? 

    I've seen comments like this many times on different sites: "One thing to note that it is common myth that turning on every second recording makes the data more accurate in terms of GPS accuracy or distance recorded or even your HR values. GPS & HR is still "sampled" every second in either mode and calculations based off those samples. It is just not "recorded" every second when in smart mode."

    Guess it still doesn't make sense how the distance could read as 2.5 km over everybody else (with different watches and settings) despite the track being pretty much exactly the same. Others have the same variation between their tracks but the total distance is much much closer. Oh well doesn't matter much anyways. Thanks again!