[time-nuts] nuts about position

Dana Whitlow k8yumdoober at gmail.com
Wed Apr 25 11:19:38 EDT 2018


While I was at the Arecibo Observatory it became desirable to get a good
surveyed position
for a new GPS antenna we had installed for the NIST TMAS system.  We found
a resource
at the Univ of Puerto Rico who had a Trimble (I think) unit.  He set it up
on the site, "turned on
the bubble machine", then left it alone for about two hours.  He returned
the estimated
position a few days later, expressing high confidence that it was good
within about 8 inches.

I'm sure I asked him if this machine used both L1 & L2, but don't recall
his answer.   I suspect
it was "yes".

Dana


On Wed, Apr 25, 2018 at 9:56 AM, Tom Van Baak <tvb at leapsecond.com> wrote:

> List -- I had a recent query by a researcher who would like to pinpoint
> the location of his telescope(s) within 0.3 meters. Also (he must be a true
> scientist) he wants to do this on-the-cheap. He may have timing
> requirements as well, but that's another posting.
>
> So I toss the GPS question to the group. Surely some of you have crossed
> the line from precise time to precise location?
>
> How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D
> position?
>
> When we run our GPSDO in survey mode how accurate a position do we get
> after an hour, or even 24 or 48 hours? And here I mean accurate, not
> stable. Have any of you compared that self-reported, self-survey result
> against an independently measured professional result or known benchmark?
>
> Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1 foot
> accuracy given enough time?
>
> If not, what improvement would -T models and RINEX-based web-service
> post-processing provide?
>
> It that's still not close enough to 0.3 m, is one then forced to use more
> expensive multi-frequency (L1/L2) or multi-band (GPS, GLONASS, Galileo) to
> achieve this level of precision? If so, how cheaply can one do this? Or is
> the learning curve more expensive than just hiring an survey specialist to
> make a one-time cm-level measurement for you?
>
> Something tells me 1 foot accuracy in position is possible and actually
> easier than 1 ns accuracy in time. I'm hoping some of you can help
> recommend solution(s) to the researcher's question or shed light on this
> interesting challenge.
>
> Thanks,
> /tvb
>
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