Related

GPS about 30m off

Edwin
3 months ago

I have noticed this twice now. After using my GPSmap 67i for a few hours the gps is at once way off.

We went for a little walk this evening to find a cache. The gps worked fine until the last waypoint. We were on the right spot and according to the gps we were 30m away from that waypoint.

In the hurry of that moment I didn't notice the fault right away, but being home in my backyard I see the gps is still way off.

Multi-GNSS is selected and Multi-Band is on. According to the Satellite page  there could be a variation of 1.8m. On the map I can see the gps is at least 30m off.

Switching the device off and on solves it directly. I had the same experience yesterday (not caching or walking at that time, just playing with this new toy at home), so it is not just a one time glitch.

I wonder if someone else has this experience as well and I hope someone can tell me I can solve this behavior by myself.

Regards,

   Edwin.

  • 0 3 months ago

    Seems I cannot edit my own message above.

    So in reply to myself I can add that switching from Multi-GNSS to GPS only gives the right location again.

    Regards,

      Edwin.

    Ah, found the "edit link" now  to edit my own messages..

  • 0 3 months ago

    Edwin, this falls in the category of advice that's too late.  But it would have been useful to know what the device said its accuracy was when it was that far off.  

  • 0 3 months ago

    Since it only occurs with multi-GNSS and resolves with a power cycle, it might be a bug. You should probably open a support ticket. 

    The fact that you can see the difference on the map causes me to wonder. Which map are you using. And what datum?

    Regardless, be aware that the accuracy estimate (that 1.8m on the satellite page) is based on probability. “There is x% probability that your actual location is within y meters of the reported location.” The choice of x is up to Garmin. This is a balancing act. Marketing vs real world. All you see is the distance. You have no idea what the fixed probability is. Typically on the order of 85%. Point is that (with that example) 15% of the time, the discrepancy will be larger than the reported accuracy.

  • 0 3 months ago
    Edwin said:
    On the map I can see the gps is at least 30m off.

    the question would be what map? Where it came from and who did it draw with what basic chart datum etc. There is no correct or wrong position, just matter of input data

  • 0 3 months ago in reply to skyeye

    There is a simpler solution than worrying about map datums in the 67i.  Type the coordinates from the 67i into Google Earth and zoom all the way in.  If the location shown is the same as the one on the map in the 67i, then it's not a map issue.  If the location shown is different by about 30m in the opposite direction of the apparent 67i map error, then a map issue is the likely reason for the discrepancy.  I presume Edwin was using the same map when he got correct positions.  So I doubt it's a map issue. 

  • 0 3 months ago

    Okay, thanks for all your replies!

    I have been trying to think of a test script that could give some insight.

    I thought that the gps, when in gnss mode, did not recover well from a bad signal reception. It seems not be the case. After a lot of trying, the test script is really simple.

    Set the gps in gnss mode, put on a (plastic) table in the backyard and wait.

    It starts really well. The gps finds it location fast and according to the map it seem quite accurate. (Standard topo Europa map that came with the device, sometimes using the satellite map layer I downloaded with the gps).

    Don´t touch the gps, just sit and wait and after about 5 minutes it is about 20 meters off.

    Then I pick up the gps, walk those 20 meters and back to the table. The gps is about on the right location as on the start of this little test a bit of though. I can now watch the coordinates change slowly until it is about 20m off again.

    I will now do this test with only gps (no gnss) and report back.

    Edit: the given variation on the gps is always 1.8m.

    Edit2: I can confirm that in gps-only mode this odd behavior does not occur.

    Regards,

       Edwin.

  • 0 3 months ago in reply to Edwin

    Edwin, your test might be easier and avoid manual record keeping if you turn on track recording and set to a fixed time interval.  

  • 0 3 months ago in reply to jlg2

    Thanks, I didn´t think of that. Will try and test some more. (Probably tomorrow).

  • 0 2 months ago

    I have the same problem, If in satellite System you configure in demo mode and after Restore default position and elevation are ok again.

    It seems it is like a cleaning.

  • 0 2 months ago

    So on holiday in Luxembourg, time to do some caches.

    Unfortunately the same problem occurred today during caching. We did about 14 caches on a row. During the last cache I noticed that according to the GPS we were not walking on the trail but a few meters off. Then reaching the cache site, according to the GPS the cache was on an impossible location. At that time I switched from Multi-GNSS to GPS only and now we were guided in the right direction, spot on and cache found.

    My advise: do not use multi-GNSS. After a while it will be 30 meters off at least.

    (One of the reasons I bought this expensive device was high accuracy because of multi-GNSS, so that's a bummer.)

    , thanks for your reply. I will try, but I doubt that switching to Demo and back will keep he gps "on the right position". Switching from multi-GNSS to GPS and back again solves this problem as well, it just does not last. As said, I will try and report back.

    Curious if Garmin Support has anything to say about this.

    Regards,

       Edwin.