Mailinglist Archive: opensuse (1420 mails)

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Re: [opensuse] openSUSE + gpsd + PPS + NTP
  • From: Roger Oberholtzer <roger@xxxxxx>
  • Date: Wed, 15 Jan 2014 15:52:18 +0100
  • Message-id: <2762031.qCpcmfM8Pv@acme>
On Wednesday, January 15, 2014 03:40:41 PM jdd wrote:

ntp is certainly not as good as a professional time keeper like the one you
have in your high end GPS. Did you ask the GPS maker about this?

You mean could the receiver act as a ntp server? I have asked. It does not do
so. The accuracy of the GPS receiver internally is only part of the issue. I
need to get that time into the PC with small error. At 90 km/h (you move 25
meters a second), an error of 0.1 seconds produces an error of 2.5 meters.
The problem is that the times in records from a GPS are when that record was
calculated. It is not the time when I see it. The difference in those times can
result in a many meters error. This is why the PPS from the GPS is
interesting. It tells when certain things are calculated in the receiver.
There is a kernel driver specifically for using the PPS signal. gpsd/ntpd use
this signal to improve interpretation of the time in the GPS data when it
eventually and non-deterministically arrives, and thus set the PC clock more
accurately.


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Yours sincerely,

Roger Oberholtzer

Ramböll RST / Systems

Office: Int +46 10-615 60 20
Mobile: Int +46 70-815 1696
roger.oberholtzer@xxxxxxxxxx
________________________________________

Ramböll Sverige AB
Krukmakargatan 21
P.O. Box 17009
SE-104 62 Stockholm, Sweden
www.rambollrst.se
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