[time-nuts] Precise manual survey (was Common sky pps...)
SAIDJACK at aol.com
SAIDJACK at aol.com
Wed Jan 7 04:05:20 EST 2009
that's a good question. Some users of our Fury use rented/borrowed survey
equipment (Leica, Javad, etc) to get a very precise position of their antenna,
or they call in a surveyor.
It is also possible to let the receiver do the auto survey multiple times,
preferably during different times of the day, then manually average the
position fixes, and enter them into our Fury unit as the new position-hold
position. I described this method some time ago. Position error should be reduced by
this type of averaging.
One could also use the Fury NMEA GPGGA output command to send NMEA position
data to a PC over a long time, say a week or more, then crunch all that data
down to one averaged position fix and manually enter it into the Fury.
And your idea of trial and error is not bad either, but I would think height
errors of <10 feet, and position errors of less than 5 feet would be
sufficient to try. This requires a good reference to compare against though, and
LOT'S of patience I would think.
>From what I can see, all commercial GPS receivers have a really tough time
generating an accurate antenna height measurement due to the way GPS works.
They don't seem to have a problem generating good long/lat coordinates. But in
timing, all three axis need to be precise unfortunately.
In a message dated 1/6/2009 03:23:53 Pacific Standard Time,
pvince at theiet.org writes:
>When we say units typically have 25ns unit-to-unit variation on the 1PPS on
>un-calibrated units, then I believe most of this is caused by the
>position errors of the GPS receiver. One could get much better performance
> manually entering the exact position-hold position of the antenna, and
>calibrating for antenna cable delay (in 1ns steps).
A naive question, if I may: how do I go about doing a precise manual
position survey? Is it simply a case of letting the unit self
survey, then manually entering different co-ordinates (say +/- 10 metres) in
each of the three directions in turn, watch the
signal output, and try to tune for minimum wobble?
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