Hi Gary, >From one NW GPS farm to another... I'm willing to help you debug yours.
> A Garmin 18x reports: > Altitude Err: +/- 264 ft Something is terribly wrong with your setup. The Garmin 18x is much, much better than this. I know because the 18x was one of the GPS receivers I brought along on a recent mobile clock experiment. Here is a plot of 2 hours of GPGGA raw altitude data while stationary in Tucson: http://leapsecond.com/great2016a/2016a-garmin-18x-2.gif With clear sky view, the peak to peak is under +/- 8 m, and the (1-sigma) standard deviation is 3 m. Even at the hotel lobby, with obstructed sky view, the (1-sigma) standard deviation stayed under 7 m. Your 18x number, +/- 264ft (+/- 80 m), is 10x to 25x worse than this. It doesn't feel right. Off-list, can you send me a day of NMEA from your 18x? Not gpsd output; but the raw serial ascii data from the receiver. I'd like to get to the bottom of this. We'll all learn something. Thanks, /tvb ----- Original Message ----- From: "Gary E. Miller" <g...@rellim.com> To: "Van Horn, David" <david.vanh...@backcountryaccess.com> Cc: <time-nuts@febo.com> Sent: Wednesday, June 08, 2016 3:24 PM Subject: Re: [time-nuts] GPS altitude somewhat wrong? Yo David! On Wed, 8 Jun 2016 20:33:58 +0000 "Van Horn, David" <david.vanh...@backcountryaccess.com> wrote: > I suppose 214' isn't that outrageous, but it does bring me to a > question: Looking at my GPS farm, fair but not great skyview. A Garmin 18x reports: Altitude Err: +/- 264 ft A u-blox 8: Altitude Err: +/- 36 ft And an adafruit HAT (u-blox 6?: Altitude Err: +/- 69 ft On a Skytraq I have seen +/- 12 feet. > How accurate is the altitude number really? Depends. :-) RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
