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Position Drift (continued from "GPS about 30m off")

jlg2

This continues from the long two-year-old thread (GPS about 30m off - GPSMAP 67i - inReach - Garmin Forums) to focus on position drift that is corrected by restarting the receiver.  The earlier thread became a catchall for a larger category of inaccuracies.  Since the position drift issue is corrected by restarting the device, I assume that narrows the possible causes.  Have firmware updates in the last two years addressed this?

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    Consumer grade GPS receivers (such as the ones Garmin makes) are not 100% accurate. There are several factors that can cause position accuracy such as GPS drift, environmental factors, and device settings. Please review the following article for additional information on these causes, as well as setting suggestions to try: Improving GPS, Distance, and Speed Accuracy of an Outdoor Handheld or GLO 2

  • 0 in reply to Garmin - AL

    Thanks, AL.  That article is not too helpful.  I suppose the person who wrote it knew what he meant to say.  But explanations like,...

    "The GPS location accuracy of Garmin handhelds is around 3 meters (10 feet), 95% of the time. This means, at any given time, your handheld will save your location within 3 meters of your actual location. If your handheld is recording a location every second and you do not pause an activity while standing still, your handheld can record up to 180 meters (590 ft) in just 1 minute. When in an area with degraded GPS signal, your handheld can record even more distance while stopped. The distance recorded while standing still is a representation of GPS Drift."

    But I suspect only someone who already knew what he meant would figure it out from that. 

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    I'd be happy with 30 m difference - mine was off over 3 km in a remote area of Alaska this summer. I was not aware of this issue. Good thing somebody had an iphone with the Gaia GPS app installed. 

  • 0 in reply to 5230657

    That's worth investigating.  How far for how long was it off position?  How was the error measured?  Where were you?  What were the satellite settings?  

  • 0 in reply to jlg2

    I kept thinking it was user error. I'd collect a waypoint, generally to a vegetation plot location or the helicopter landing spot. When trying to navigate back to the spot on the same day, the distance to the point would be over 3 km when I knew it was only a few hundred meters. 

    I thought somehow I had set the GPS so it was navigating from a different waypoint rather than my current location, but couldn't find a way to do that even if I wanted. As noted in other articles, as I got close to the desired location the distance and navigation seemed to correct itself.

    This tended to happen with waypoints collected in the morning, so I think there was poor satellite alignment at that time; later waypoints seemed to work okay. We had a second crew using another Garmin GPSMAP 67i and when I sent waypoints to them using the "Share Wirelessly" function the problem carried over. To the best of my knowledge, they weren't getting the same error when recording waypoints, but they tended to be collecting points later in the morning when there was perhaps better satellite alignment. But, satellite alignment doesn't explain why my teammate with Gaia GPS on an iphone was getting good locations when recording waypoints at the same time. Firmware was up to date. 

    I was working about 50 - 60 miles northeast of Ft. Yukon, AK. Satellite settings are Multi-GNSS with multiband on. We were not under heavy canopy - we were in a year old burn. Sites were pretty flat. When I checked the error on the satellite page, it always said 1.8 - 2 m, although I didn't check for every plot. Averaging locations when collecting the waypoints didn't seem to make much difference. I don't really trust the error estimates on the newer Garmins - preferred the way older units reported it and preferred their method for averaging locations. 

    When I downloaded points into ArcGIS, I had points for both the actual and the incorrect locations, both labelled with the plot number.