[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [gpsd-users] Garmin 18X-5Hz
From: |
Gary E. Miller |
Subject: |
Re: [gpsd-users] Garmin 18X-5Hz |
Date: |
Mon, 15 Aug 2016 10:57:17 -0700 |
Yo Robin!
On Mon, 15 Aug 2016 13:22:06 +0200
Robin Schwab <address@hidden> wrote:
> Hi Gary
>
> Am 14.08.2016 um 23:14 schrieb Gary E. Miller:
> > No, I mean hard fail. Like loss of signal, no PPS output, so ntpd
> > goes free running. Or worse yet, just a wild hare output., like 14
> > Aug about 16:00 UTC here: https://pi2.rellim.com/day/
> >
> > Tht one happens every few weeks, driving me crazy to find and fix.
>
> I think you have already seen how inaccurate a GPS can be with poor
> signal i.e. when you come out of a tunnel. There is a huge difference
> in precision between any fix and a good fix.
And who runs a time server in a tunne;?
> NMEA Dilution Of Precision (DOP) values are available so I see no
> point in not using them. Ublox modules send even a specific Time DOP
> signal (PUBX,00,…). When you have a bad fix in a stream of good fixes
> the bad fix should get discarded. Maybe just a bird sitting on your
> antenna :-)
gpsd does discard bad time fixes. It does so using the manufactureres
recommened method, which is to only use time stamps when the GPS has
had 3 valid fixes in a row.
If you can come up with something better, and can prove it with some
graphs, we'd ike to hear about it.
> Would be interesting to see if that solves your problem.
Dunno. Until I find the problem I don't know what it is not. Right
now I'm just collecting data, and that is a slow process with something
that may happen once a month.
> > If you are only going to have one input you should be using
> > chronyd.
>
> I'll consider using chrony. I do see the point of NTPd providing a
> robust networks of clocks that are maybe 1s accurate for login
> purposes.
As always, YMMV. So run stats and tell us what you see.
> But if you have a GPS clock that is <1us accurate (it has to be
> because otherwise the position would be wrong)
I have lots of scatter plots showing wrong GPS!
> I do not see the
> advantage of correcting that time with a network peer clock that is
> >100 ms away.
Who said 100 mSec? Not me! Your strawman is of no use to me. You
assume away the problem this corrects: bad output from you GPS. It
happens. As you said, a bird could land on your antenna.
> You can use those network clocks for statistics and
> >cross-checking but
> basically you have to trust your own GPS clock.
Trust, but verify. GPS have a huge failure rate around leap second
time. Come next January 1st tell me how well standalone time servers
did. If last time is any guide....
> Of course ntpd
> accounts for the latency over the network
wishful thinking...
> but since the latency is
> big and varies the correction can't be that good.
I get 9 milliSec to NIST in Seattle. 10 microSec or better to my other
local chimers. The errors on my Pi2/Adafruit tend to be +/1 1 Sec.
RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
address@hidden Tel:+1 541 382 8588
pgp31mWoucDKb.pgp
Description: OpenPGP digital signature
- Re: [gpsd-users] Garmin 18X-5Hz, (continued)
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Frank Nicholas, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/12
- Re: [gpsd-users] Garmin 18X-5Hz, Robin Schwab, 2016/08/13
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/13
- Re: [gpsd-users] Garmin 18X-5Hz, David J Taylor, 2016/08/14
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/14
- Re: [gpsd-users] Garmin 18X-5Hz, Robin Schwab, 2016/08/14
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/14
- Re: [gpsd-users] Garmin 18X-5Hz, Robin Schwab, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz,
Gary E. Miller <=
- Re: [gpsd-users] Garmin 18X-5Hz, Robin Schwab, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Alexander Carver, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Alexander Carver, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Alexander Carver, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Alexander Carver, 2016/08/15
- Re: [gpsd-users] Garmin 18X-5Hz, Gary E. Miller, 2016/08/15