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Half-marathon distance measured by gps only

Alexander
over 2 years ago

Is anyone experiencing the same type of "accuracy"? In gps only, my Garmin 910xt/ 920xt/ 945 performed way better.

  • 0 over 2 years ago

    Hi Alexander

    No my watch is usually quite close to officially measured distances.

    it is not possible to say whether your watch is way off or not. Did you let your watch soak for a few minutes before you started your watch? How big buildings where around you on your run? Did you run the "blue-linee" or not (this is mostly interesting when your track is to long and not to short). 

    If you share your fit-file/link to garmin connect then it is probably easier to see what could be the reason.

  • 0 over 2 years ago in reply to parentoft

    1. I did get a full on green bar a few minutes before the start

    2. Big buildings threw me off my pace from a 5:12/ km to a 6:30ish/ km

    3.https://connect.garmin.com/modern/activity/9756359915

    4. Same course, measured by Stryd in the past, anywhere from 20.9 to 21.2 at most

  • 0 over 2 years ago in reply to Alexander

    Something is indeed very weird there...

    Some km markers seem way off, the 1km is already at 2km distance for example... (I actually retracked the map in a distance calculator tool).

    Then they are ok until the 8k mark, which is too far from the 7k mark but the 9k mark is too close to the 8k which 'corrects' that part...

    Didn't look further (I started trackign because I noticed the 7, 8, 9k part initially). But also from 11 to 12 it seems to far, then something iffy going on in 12, 13, 14, 15 area...

    However, pace doesn't seem to be influenced by the first 10k 'weirdness' so might just be a course plot thing. Looks iff at 14-16k regarding pace, but loosing a km there is a LOT.

    Not sure, I never use GPS only but haven't noticed anything like this using multiband

  • 0 over 2 years ago in reply to Alexander

    Hi Alexander

    As FlipStone is writing something seems wrong with tracked route. It is perfect if you have been doing the same run last year (or before). Especially if you got Stryd - Stryd measures the distance perfectly when you got bad GPS-tracking (I've seen quite a lot of that e.g. in Paris).

    Export your route to two GPX files. One, that is wrong and one that is OK. Save the files to your cmputer desktop.

    Jump to https://gtt.feub.net/compare-tracks/ and upload the two files and do a compare. Then you can see where your wrong data is off.

    You can also try to upload the files to http://www.mygpsfiles.com/app/

    If you want the more detailed version of where it might go wrong - then download QGIS (it is a 1 gig download). https://www.qgis.org/en/site/index.html

    Here you can upload your GPS file at ask it to you how much offf you have been (it can show every single registration of your GPS-data) and then you visually should be able to get an idea of where it went wrong.

    /Palle


  • 0 over 2 years ago in reply to parentoft

    Hi Parentoft,

    Thank you very much for the info. I have been struggling with my FR955 suddenly showing my morning walking distances that are 6-7% short of what I was used to (on trails I use frequently). I then used my Fenix 7s SS simultaneously and it showed the distance I expected. The compare track tool shows that the FR955 track seems OK but with the tool calculated distance 6-7% longer than shown on the watch. The 7s track was a bit smoother with the identical distance as in the watch. I am not sure what happened to the FR955 (factory reset didn't fix it) but it seems that it was a result of the 12.25 beta that carried over to the 12.27.