[time-nuts] Imagery position accuracy

Miguel Barbosa Gonçalves m at mbg.pt
Mon May 6 18:38:05 EDT 2013

On 6 May 2013 03:21, Chris Albertson <albertson.chris at gmail.com> wrote:

> After you get the position, how does the OP (or anyone else) put the
> location data into the Trimble GPS receiver so that it can be used in
> the time solution.  This is for NTP remember.

Hi Chris!

You can input the information through the Windows application and tell it
to not self-survey.

> Assuming there is some way, will the Trimble GPS receiver "remember"
> the location over a power cycle?

The position as all the configuration is stored in the EPROM when one
issues a command on the Windows interface.

> In other words, is there a way to program a Trimble receiver to NOT do
> the self-survey on power up and instead to use some survey location
> you got by some other method, like possibly hiring a survey team.


> If there is a why to make that work, I might even modify the NTP
> driver to do it.

You'll have to make the driver talk to the configuration / monitoring port
(port B) as the timing port (port A) does not accept commands.

I thought about sending the configuration commands to port B and get the
time from port A. The problem with this is that you can't raise the RTS pin
to request a time packet from the receiver (they call this event
something... can't remember). What I did in the end was to use two
RS422-to-RS232 converters so I can use the driver normally through port A
and then set the receiver and see the birds it is following on port B. I've
also used the PPS+ signal and connected it to the DCD pin. Just completed
this project a few minutes ago. The machine has been running for a few

acutime# uptime; ntpq -p; ntptime
10:34PM  up 31 mins, 1 user, load averages: 0.00, 0.00, 0.00
     remote           refid      st t when poll reach   delay   offset
*GPS_PALISADE(0) .GPS.            0 l   12   16  377    0.000    1.073
oPPS(0)          .PPS.            0 l   10   16  377    0.000    0.077
ntp_gettime() returns code 0 (OK)
  time d532ae7f.98b1edec  Mon, May  6 2013 22:34:39.596, (.596465965),
  maximum error 6000 us, estimated error 1 us, TAI offset 0
ntp_adjtime() returns code 0 (OK)
  modes 0x0 (),
  offset 72.469 us, frequency 143.112 ppm, interval 256 s,
  maximum error 6000 us, estimated error 1 us,
  time constant 4, precision 0.001 us, tolerance 496 ppm,
  pps frequency 143.112 ppm, stability 0.234 ppm, jitter 0.663 us,
  intervals 29, jitter exceeded 23, stability exceeded 0, errors 3.

My configuration

server mode 3 minpoll 4 maxpoll 4 prefer
# Event polling (flag2 0)
fudge flag2 0

# PPS driver capture on rising (flag2 0) and kernel PPS active (flag3 1)
server minpoll 4 maxpoll 4
fudge flag2 0 flag3 1

statsdir /var/log/ntp/
filegen peerstats file peers type day link enable
filegen loopstats file loop type day link enable
filegen clockstats file clock type day link enable

With this configuration I can stop using the PALISADE driver and configure
the Acutime to send NMEA sentences and use the PPS for better accuracy.


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