Discussion:
nuts about position
(too old to reply)
Tom Van Baak
2018-04-25 14:56:14 UTC
Permalink
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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George Watson
2018-04-25 15:06:34 UTC
Permalink
Create your own DGPS?

Trimble is good at this.

George K. Watson
K0IW
Post by Tom Van Baak
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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Mark Spencer
2018-04-25 16:30:49 UTC
Permalink
This link seems to provide an overview of Differential GPS and some related techniques.

https://www.e-education.psu.edu/geog862/node/1834

Building a system along these lines from "auction site purchases" and home brewed computer code might be a fun project but one would presumably need an accurately surveyed starting point.


Mark Spencer

***@alignedsolutions.com
604 762 4099
Post by George Watson
Create your own DGPS?
Trimble is good at this.
George K. Watson
K0IW
Post by Tom Van Baak
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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Scott McGrath
2018-04-26 17:04:54 UTC
Permalink
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its about 600 bucks minus antenna.

You would need a choke ring antenna to get centimeter accuracy i think but receiver with a quality timing antenna will provide necessary accuracy

On Apr 25, 2018, at 8:06 AM, George Watson <***@sierracmp.com> wrote:

Create your own DGPS?

Trimble is good at this.

George K. Watson
K0IW
Post by Tom Van Baak
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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Gary E. Miller
2018-04-26 19:08:48 UTC
Permalink
Scott!

On Thu, 26 Apr 2018 10:04:54 -0700
Post by Scott McGrath
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its
about 600 bucks minus antenna.
Link? With RTK in the name it prolly needs a base and rover? Or post
processing?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
***@rellim.com Tel:+1 541 382 8588

Veritas liberabit vos. -- Quid est veritas?
"If you can’t measure it, you can’t improve it." - Lord Kelvin
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Tim Lister
2018-04-26 20:59:18 UTC
Permalink
Post by Gary E. Miller
Scott!
On Thu, 26 Apr 2018 10:04:54 -0700
Post by Scott McGrath
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its
about 600 bucks minus antenna.
Link? With RTK in the name it prolly needs a base and rover? Or post
processing?
It's this one: https://www.swiftnav.com/piksi-multi One thing to bear
in mind is it only L2C, the new civilian channel on the lower
frequency L2 band. This is not available on approx. 1/2 of the
satellites currently. There are several articles evaluating in
comparison with e.g. a ublox M8T at
https://rtklibexplorer.wordpress.com/tag/swift-piksi-multi/
Post by Gary E. Miller
RGDS
GARY
Cheers,
Tim
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Bob kb8tq
2018-04-26 19:12:28 UTC
Permalink
Hi

If you shop for a while on eBay, you can find older L1 / L2 survey receivers for < $300 and
an antenna that will work for them for < $100. Yes it will take a bit of heavy duty shopping and
some level of “wait and see”. How well they work and how much of a pain is associated with
this process ….. who knows.

Once you have a radio you can get data out of, submitting the files to any of the free services
in the US is pretty easy. If you are outside the US, you may still be fine or you may have a tough
time with the data reduction.

Bob
Post by Scott McGrath
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its about 600 bucks minus antenna.
You would need a choke ring antenna to get centimeter accuracy i think but receiver with a quality timing antenna will provide necessary accuracy
Create your own DGPS?
Trimble is good at this.
George K. Watson
K0IW
Post by Tom Van Baak
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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Michael Wouters
2018-04-27 00:15:20 UTC
Permalink
The US-based services work fine with non-local data. I've used them with
Australian locations. The IGS network is global so nearby stations in the
IGS network are used for the solution. There are non-US services too, like
AusPos.

The topic of better antenna coordinates seems to come up now and again. It
might be a good cooperative timenuts project to put together a travelling
receiver system that could be used to survey antenna positions. With a bit
more effort, it could also be used to calibrate delays, where receiver data
is being post-processed for time-transfer.

Cheers
Michael
Post by Bob kb8tq
Hi
If you shop for a while on eBay, you can find older L1 / L2 survey receivers for < $300 and
an antenna that will work for them for < $100. Yes it will take a bit of
heavy duty shopping and
some level of “wait and see”. How well they work and how much of a pain
is associated with
this process ….. who knows.
Once you have a radio you can get data out of, submitting the files to any
of the free services
in the US is pretty easy. If you are outside the US, you may still be fine
or you may have a tough
time with the data reduction.
Bob
Post by Scott McGrath
Swiftnav has a centimeter accurate multi band receiver RTK-585. Its
about 600 bucks minus antenna.
Post by Scott McGrath
You would need a choke ring antenna to get centimeter accuracy i think
but receiver with a quality timing antenna will provide necessary accuracy
Post by Scott McGrath
Create your own DGPS?
Trimble is good at this.
George K. Watson
K0IW
Post by Tom Van Baak
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.
Post by Scott McGrath
Post by Tom Van Baak
So I toss the GPS question to the group. Surely some of you have
crossed the line from precise time to precise location?
Post by Scott McGrath
Post by Tom Van Baak
How easy, how cheap, how possible is it to obtain 0.3 m accuracy in 3D
position?
Post by Scott McGrath
Post by Tom Van Baak
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?
Post by Scott McGrath
Post by Tom Van Baak
Do you know if cheap ublox 5/6/7/8 series receivers are capable of 1
foot accuracy given enough time?
Post by Scott McGrath
Post by Tom Van Baak
If not, what improvement would -T models and RINEX-based web-service
post-processing provide?
Post by Scott McGrath
Post by Tom Van Baak
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?
Post by Scott McGrath
Post by Tom Van Baak
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.
Post by Scott McGrath
Post by Tom Van Baak
Thanks,
/tvb
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Post by Scott McGrath
Post by Tom Van Baak
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Mark Sims
2018-04-25 15:16:10 UTC
Permalink
When in was developing Lady Heather's precision survey code I was comparing the calculated positions to those from an Ashtech Z12 dual freq GPS (with the position calculated by OPUS). Using the same survey grade antenna and a Thunderbolt the results were usually within a meter. I have not tried it using a more modern GPS receiver.
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Dana Whitlow
2018-04-25 15:19:38 UTC
Permalink
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
Post by Tom Van Baak
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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Tim Lister
2018-04-25 15:38:48 UTC
Permalink
Post by Tom Van Baak
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.
Hi Tom, list, as another researcher who is also interested in
telescope positions (!) I have done this for personal use at home with
a ublox 6T and 53532A antenna to see what I got. I was logging in the
UBX binary format with the raw (carrier phase) measurements turned on
and then converting it to RINEX and using the NRC's CSRS-PPP online
service which is one of the few that will take single frequency L1
only data. The results based on approx. 41.5 hours of data and which
were post-processed 21 days later (so that they used the IGS Final
products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of
0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal
height respectively. I was quite impressed with the results without
use of the L2 frequency to correct for the ionosphere etc.
Post by Tom Van Baak
Thanks,
/tvb
Cheers,
Tim
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J. Grizzard
2018-04-25 20:57:18 UTC
Permalink
I think to really be confident about a position you really need the
dual-frequency data (or that data from a nearby reference station),
otherwise you could end up in a situation where you're consistent, but
that consistency has a bias. IIRC, anyhow -- I'm not sure how the math
actually works out.

Anyhow, I play around with PPP stuff on occasion, and the last run I did
was in November using the Novatel OEM628 kit that was briefly available
for cheap on eBay, and the included 702-GG antenna (which, conveniently,
has calibrations available). Running a day's worth of data through
CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and
0.024m in elevation. I've done some shorter runs since then that appear
to fall in that same range ... I really need to do a few more full runs
and see what kind of variance there is.

At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even
takes solid earth tides into account, though I didn't do that because I
was never able to figure out which specific type of solid earth tide
data I needed. I imagine there's still some issues with any given datum
being somewhat imperfect, as far as altitude is concerned, and I don't
really know how to correctly deal with that if exact altitude matters.
Maybe we should all just agree to use XYZ/ECEF coordinates for
everything and give up on this whole altitude thing altogether... ;)

(As an aside, I've been tempted to get someone to come professionally
survey my antenna and tell me where it _actually_ is, so I could see how
well I could actually do with my GPS kit, but I imagine it's pretty
expensive -- anyone happen to know what getting that kind of thing done
actually ends up costing?)

-j
Post by Tim Lister
Post by Tom Van Baak
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.
Hi Tom, list, as another researcher who is also interested in
telescope positions (!) I have done this for personal use at home with
a ublox 6T and 53532A antenna to see what I got. I was logging in the
UBX binary format with the raw (carrier phase) measurements turned on
and then converting it to RINEX and using the NRC's CSRS-PPP online
service which is one of the few that will take single frequency L1
only data. The results based on approx. 41.5 hours of data and which
were post-processed 21 days later (so that they used the IGS Final
products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of
0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal
height respectively. I was quite impressed with the results without
use of the L2 frequency to correct for the ionosphere etc.
Post by Tom Van Baak
Thanks,
/tvb
Cheers,
Tim
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Brooke Clarke
2018-04-26 02:46:01 UTC
Permalink
Hi J:

I had a number of survey stakes I placed using a manual transit and tape measure and hired a local surveyor to tell me
where they were and also tell me where my GPS antenna was located.

He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total station on another tripod and ran a cable
between the two.  After some time (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS
antenna.  I got a report back in a week or so.  Total cost a few hundred dollars.

I'm in the process of looking at how accurate the GPS is in my new LG G6 phone.
--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

-------- Original Message --------
I think to really be confident about a position you really need the dual-frequency data (or that data from a nearby
reference station), otherwise you could end up in a situation where you're consistent, but that consistency has a
bias. IIRC, anyhow -- I'm not sure how the math actually works out.
Anyhow, I play around with PPP stuff on occasion, and the last run I did was in November using the Novatel OEM628 kit
that was briefly available for cheap on eBay, and the included 702-GG antenna (which, conveniently, has calibrations
available). Running a day's worth of data through CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude,
and 0.024m in elevation. I've done some shorter runs since then that appear to fall in that same range ... I really
need to do a few more full runs and see what kind of variance there is.
At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even takes solid earth tides into account, though
I didn't do that because I was never able to figure out which specific type of solid earth tide data I needed. I
imagine there's still some issues with any given datum being somewhat imperfect, as far as altitude is concerned, and
I don't really know how to correctly deal with that if exact altitude matters. Maybe we should all just agree to use
XYZ/ECEF coordinates for everything and give up on this whole altitude thing altogether... ;)
(As an aside, I've been tempted to get someone to come professionally survey my antenna and tell me where it
_actually_ is, so I could see how well I could actually do with my GPS kit, but I imagine it's pretty expensive --
anyone happen to know what getting that kind of thing done actually ends up costing?)
-j
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jimlux
2018-04-26 03:39:31 UTC
Permalink
Post by Brooke Clarke
I had a number of survey stakes I placed using a manual transit and tape
measure and hired a local surveyor to tell me where they were and also
tell me where my GPS antenna was located.
He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total
station on another tripod and ran a cable between the two.  After some
time (tens of minutes or ??) he used the theodolite to sight my stakes
and the GPS antenna.  I got a report back in a week or so.  Total cost a
few hundred dollars.
I'm in the process of looking at how accurate the GPS is in my new LG G6 phone.
Yep - A typical total station is good to "a few seconds" (some single
digit mm at 100 meters) in angle. Distance is usually pretty accurate
1.5 mm + 2ppm.

So over a typical 100m sort of size (several acres) a total station can
provide relative positions to better than a cm, but probably not better
than a mm.

A good optical theodolite can do *maybe* an order of magnitude better,
in terms of the basic measurement, but then there's other confounding
factors that might dominate.

For instance, are you sure you're holding the prism/target *precisely*
over the mark? And just what *is* that mark.

Precision metrology in any field is fascinating, but a rabbit hole down
which one can fall very, very deep.


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Bob kb8tq
2018-04-26 12:42:58 UTC
Permalink
Hi

On something like a phone, you are likely looking at a combination of what the
phone does and a contribution from “the cloud”. Part of that cloud contribution
depends a bit on the carrier and how well they are doing their part of things. In
one area you might have surveyed towers and a full GPS / Glonass synthesis.
If you bought your service from Crazy Bob, there may be no local correction
information. Forget about GPS / Glonass in that case (at least in the US).

Bob
I had a number of survey stakes I placed using a manual transit and tape measure and hired a local surveyor to tell me where they were and also tell me where my GPS antenna was located.
He setup a GPS antenna on one tripod and a (Trimble?) combined GPS-total station on another tripod and ran a cable between the two. After some time (tens of minutes or ??) he used the theodolite to sight my stakes and the GPS antenna. I got a report back in a week or so. Total cost a few hundred dollars.
I'm in the process of looking at how accurate the GPS is in my new LG G6 phone.
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
-------- Original Message --------
I think to really be confident about a position you really need the dual-frequency data (or that data from a nearby reference station), otherwise you could end up in a situation where you're consistent, but that consistency has a bias. IIRC, anyhow -- I'm not sure how the math actually works out.
Anyhow, I play around with PPP stuff on occasion, and the last run I did was in November using the Novatel OEM628 kit that was briefly available for cheap on eBay, and the included 702-GG antenna (which, conveniently, has calibrations available). Running a day's worth of data through CSRS-PPP produced sigmas (95%) of 0.004m latitude, 0.008m longitude, and 0.024m in elevation. I've done some shorter runs since then that appear to fall in that same range ... I really need to do a few more full runs and see what kind of variance there is.
At any rate, theoretically you can get ^^^ that close, anyhow. CSRS even takes solid earth tides into account, though I didn't do that because I was never able to figure out which specific type of solid earth tide data I needed. I imagine there's still some issues with any given datum being somewhat imperfect, as far as altitude is concerned, and I don't really know how to correctly deal with that if exact altitude matters. Maybe we should all just agree to use XYZ/ECEF coordinates for everything and give up on this whole altitude thing altogether... ;)
(As an aside, I've been tempted to get someone to come professionally survey my antenna and tell me where it _actually_ is, so I could see how well I could actually do with my GPS kit, but I imagine it's pretty expensive -- anyone happen to know what getting that kind of thing done actually ends up costing?)
-j
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Tim Lister
2018-04-30 00:45:51 UTC
Permalink
Post by Tim Lister
Post by Tom Van Baak
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.
Hi Tom, list, as another researcher who is also interested in
telescope positions (!) I have done this for personal use at home with
a ublox 6T and 53532A antenna to see what I got. I was logging in the
UBX binary format with the raw (carrier phase) measurements turned on
and then converting it to RINEX and using the NRC's CSRS-PPP online
service which is one of the few that will take single frequency L1
only data. The results based on approx. 41.5 hours of data and which
were post-processed 21 days later (so that they used the IGS Final
products rather than the Rapids or Ultra Rapids) were Sigmas(95%) of
0.105 m, 0.089 m, 0.217 m in latitude, longitude and ellipsoidal
height respectively. I was quite impressed with the results without
use of the L2 frequency to correct for the ionosphere etc.
It has taken me quite a bit longer that I had hoped but I have finally
published a writeup and howto of collecting raw ublox data, converting
it to RINEX and how to do (or get the NRC experts to do) the
post-processing. It's at a new website I have setup:
https://adventuresinprecision.space/howtos/precise-gps-positions/
Please let me know any comments or suggestions you have to improve it
or make it more comprehensible and comprehensive.

I have also been doing some experiments with RTK solutions with local
precise base stations and receiving NTRIP correction messages over
RTCM. This is looking very promising but I need to do some more
experiments (and as detailed in the howto, wait for some more precise
products to be available to compare it with...)

Cheers,
Tim
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Achim Gratz
2018-04-30 18:41:32 UTC
Permalink
Post by Tim Lister
It has taken me quite a bit longer that I had hoped but I have finally
published a writeup and howto of collecting raw ublox data, converting
it to RINEX and how to do (or get the NRC experts to do) the
https://adventuresinprecision.space/howtos/precise-gps-positions/
Please let me know any comments or suggestions you have to improve it
or make it more comprehensible and comprehensive.
Thanks for taking the time to write that up. Out of curiosity, how far
away from the RINEX coordinates is an RMS or median of the original
coordinates as recorded by the GPS and how does the convergence curve
look like? I'm trying to gauge how long I need to run my timing module
in survey mode…


Regards,
Achim.
--
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+

Wavetables for the Waldorf Blofeld:
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables
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Bob kb8tq
2018-04-30 19:34:47 UTC
Permalink
Hi

If you are looking at doing a self survey on a timing module, there is a lot
of information in the archives. It turns out that (like it or not) there is very
likely to be a ~24 hour periodicity in your self survey data. Therefor something
like a two, three, or four day survey will enhance your position estimate.

Again - for all get gory details dig into the archives.

Since the timing is done against the module’s “best estimate” of it’s position,
there isn’t a lot of benefit in having a surveyed correct position instead. More
or less, the same errors that goofed the position also goof the timing in the
same direction. Again, info in the archives.

Bob
Post by Achim Gratz
Post by Tim Lister
It has taken me quite a bit longer that I had hoped but I have finally
published a writeup and howto of collecting raw ublox data, converting
it to RINEX and how to do (or get the NRC experts to do) the
https://adventuresinprecision.space/howtos/precise-gps-positions/
Please let me know any comments or suggestions you have to improve it
or make it more comprehensible and comprehensive.
Thanks for taking the time to write that up. Out of curiosity, how far
away from the RINEX coordinates is an RMS or median of the original
coordinates as recorded by the GPS and how does the convergence curve
look like? I'm trying to gauge how long I need to run my timing module
in survey mode…
Regards,
Achim.
--
+<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+
http://Synth.Stromeko.net/Downloads.html#BlofeldUserWavetables
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Bob kb8tq
2018-04-25 16:06:45 UTC
Permalink
Hi

That sort of accuracy is pretty normal for a survey device. He needs to find a local surveyor who
likes to look at stars :). I assume the telescope is not mobile and it’s a one time sort of thing. If
he likes to romp around the question becomes how quickly he needs the location information.
Post processing is very much part of getting this done. That takes a while (like days .. weeks … months).

Bob
Post by Tom Van Baak
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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Dan Kemppainen
2018-04-25 17:07:07 UTC
Permalink
Hi,

Anecdotal response.

A few years back we played with using handheld garmin units (GPSMAP
62st) for locating property lines and corners. We averaged for 6 to 12
hours at known standards (section corners). This data was used to
subdivide the section for property corner locations, and these corners
were marked.

The method for marking was to park the GPS close to the calculated
corner location in Lat/Lon. Then we let the GPS survey for the same 6-12
hour period, corrected the GPS position and repeated until the desired
corner was located.

A year or two later due to a power line upgrade, many of the properties
were surveyed professionally. We're in a small community and we got
chatting with the surveyors. We helped them find roads/trails to get to
section corners they needed to get to. They in turn helped us by marking
the property corners in question with survey grade equipment (They said
accurate to within an inch). The handheld GPS units were within about a
foot or so of the professional units.

Obvious concerns aside, what we were really doing was dividing
relatively short distances (1 mile) between existing point into even
shorter distances between the points. The limiting factor was really
number of digits in the average reported Lat/Lon positions from the GPS.

That said, with a few good reference points (section corners, or other
standards) near the telescope and some time using a good handheld GPS
and some careful math you should be able to drill down close to 0.3m
level of accuracy.

We did want to repeat the tests with timing mode receivers set to
average for 48 hours, but haven't got around to it yet.

Dan
Message: 6
Date: Wed, 25 Apr 2018 07:56:14 -0700
To: "Discussion of precise time and frequency measurement"
Subject: [time-nuts] nuts about position
Content-Type: text/plain; charset="iso-8859-1"
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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Bob kb8tq
2018-04-25 19:08:13 UTC
Permalink
Hi

One of the “interesting features” of the ongoing bridge rebuilding process around here is the
destruction of most of the benchmark locations. They were built into the old bridges and went
away when the new ones went up. Now there are cute little brass disks on the new bridges.
There is no information on the disk and no obvious plan to generate that data ….. When one
asks about it, the answer is: “nobody does it that way anymore”.

Bob
Post by Dan Kemppainen
Hi,
Anecdotal response.
A few years back we played with using handheld garmin units (GPSMAP 62st) for locating property lines and corners. We averaged for 6 to 12 hours at known standards (section corners). This data was used to subdivide the section for property corner locations, and these corners were marked.
The method for marking was to park the GPS close to the calculated corner location in Lat/Lon. Then we let the GPS survey for the same 6-12 hour period, corrected the GPS position and repeated until the desired corner was located.
A year or two later due to a power line upgrade, many of the properties were surveyed professionally. We're in a small community and we got chatting with the surveyors. We helped them find roads/trails to get to section corners they needed to get to. They in turn helped us by marking the property corners in question with survey grade equipment (They said accurate to within an inch). The handheld GPS units were within about a foot or so of the professional units.
Obvious concerns aside, what we were really doing was dividing relatively short distances (1 mile) between existing point into even shorter distances between the points. The limiting factor was really number of digits in the average reported Lat/Lon positions from the GPS.
That said, with a few good reference points (section corners, or other standards) near the telescope and some time using a good handheld GPS and some careful math you should be able to drill down close to 0.3m level of accuracy.
We did want to repeat the tests with timing mode receivers set to average for 48 hours, but haven't got around to it yet.
Dan
Message: 6
Date: Wed, 25 Apr 2018 07:56:14 -0700
To: "Discussion of precise time and frequency measurement"
Subject: [time-nuts] nuts about position
Content-Type: text/plain; charset="iso-8859-1"
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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Brooke Clarke
2018-04-25 18:18:30 UTC
Permalink
Hi Tom:

I have a friend who bought a house on a hill so that he could build an observatory with an excellent view of the sky. 
The telescope mount is the Paramount by Software Bisque.  This mount is capable of pointing accuracy measured in a small
number of arc seconds.  That implies the control software knows the time to a high precision. But there's no "time nuts"
clock involved.  The control PC computer only has the stock NTP function turned on the in the clock.

To get that pointing accuracy he uses TPoint software that models the mechanical errors in the mount.  As part of the
start up procedure he points to a know star or stars and that sets the clock.  I expect that the location of the
telescope is determined as part of the TPoint alignment process that looks at a large number of stars.

PS We used the gun laying function of the DAGR GPS receiver when laying out the observatory to get a North-South line.
http://prc68.com/I/DAGR.shtml#GLS

As part of a FireWise community mapping process I'd like to get GPS coordinates of the fire hydrants (Lat, Lon, Ele). 
Is there a civilian GPS receiver that makes use of WAAS and/or DGPS corrections?
--
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html

-------- Original Message --------
Post by Tom Van Baak
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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jimlux
2018-04-26 01:21:10 UTC
Permalink
Post by Brooke Clarke
As part of a FireWise community mapping process I'd like to get GPS
coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian
GPS receiver that makes use of WAAS and/or DGPS corrections?
I think almost all handheld receivers these days use WAAS for improved
performance. WAAS should give you 1 meter kind of accuracy,
particularly if you compare a known location in the area.

DGPS was a thing back in the 90s (I fooled with a Trimble Scout with a
pod that received corrections over FM broadcast SCA) - I'm not sure it's
widely used today.

The USCG DGPS transmits corrections on MF beacons, but is being
decommissioned. Most of the inland stations have been shutdown.


If you're a surveyor, you get corrections from a network (CORS or
something similar), or you're primarily interested in "relative"
position - you set up your base station and your RTK rover tells you
where it is within 1 mm + 1ppm of distance from base.

http://www.xyht.com/ has regular features on the latest GPS survey gear.

You might be able to convince the local survey equipment rental house to
come out and demo the gear (or give you a good price on a rental)

Or, why not just do the survey optically (!) - none of this new fangled
GPS stuff. Rod, level, theodolite. If Everest could do it in the 19th
century in India, you can do it too.

If you can find a couple benchmarks to work from, you can get accuracy
of 1 part in 1000 with a decent 200 foot tape measure and something to
sight with (a cheap laser level at night works pretty good to keep your
line straight). You're doing a series of triangles - SSS completely
defines it, so no angles need be measured.

With decent survey gear 1 part in 10,000 or so is straightforward.

1 ppm is hot stuff with conventional optical gear - you're going to be
making multiple measurements, compensating for refraction, etc. It's
like GPS at 10cm accuracy - lots of things cause errors of that magnitude.

A nice theodolite (like a Wild T2) is readable to 1 second of arc.
That's about 5 microradian. At 100 meters, the horizontal uncertainty
would be 0.5mm. Yeah, not quite 1ppm, although you could probably do
multiple setups and average in on 1ppm.

Of course, you'll then need to go out and get a decent tripod, a rod and
target, and a rod person to wave the rod, etc.

But another poster did comment on "why not use the telescope" you could
precision point to a series of stars and calculate using celestial nav
where you are. Although, that might be painful to the 1 meter sort of
accuracy - the "tables" probably don't really account for deviations
from ellipsoid and so forth.

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Dana Whitlow
2018-04-26 04:24:44 UTC
Permalink
It is true that most handheld GPS receivers have WAAS capability these
days; however the accuracy is more like 3 to 4 meters even with several
minutes of averaging. I've always been puzzled by why it is so much
worse than good professional equipment can apparently achieve with
similar "features". Perhaps it has something to do with the simple antennas
that handheld units use.

A day or two ago I had related the story of our survey at the Arecibo
observatory done with professional equipment. Soon after that was
done, I took my handheld Garmin GPS60CX up on the roof and used it
to make the same measurement with WAAS corrections turned on and
about 10 min of averaging. I don't remember the exact numbers for
the discrepancies between the two measurements, but they were in the
neighbor hood of 4 meters. In fairness to the handheld, I should mention
that the position involved did not offer complete sky visibility- it was in
sort of a canyon such that the sky was visible only down to about 30
or 40 deg elevation to the east and west but with excellent low-elevation
visibility to the north and south.

Incidentally, Puerto Rico does have a WAAS ground station fairly close
to the observatory site, just off the San Juan airport roughly 50 miles
away from the observatory.

Dana
Post by jimlux
Post by Brooke Clarke
As part of a FireWise community mapping process I'd like to get GPS
coordinates of the fire hydrants (Lat, Lon, Ele). Is there a civilian GPS
receiver that makes use of WAAS and/or DGPS corrections?
I think almost all handheld receivers these days use WAAS for improved
performance. WAAS should give you 1 meter kind of accuracy, particularly
if you compare a known location in the area.
DGPS was a thing back in the 90s (I fooled with a Trimble Scout with a pod
that received corrections over FM broadcast SCA) - I'm not sure it's widely
used today.
The USCG DGPS transmits corrections on MF beacons, but is being
decommissioned. Most of the inland stations have been shutdown.
If you're a surveyor, you get corrections from a network (CORS or
something similar), or you're primarily interested in "relative" position -
you set up your base station and your RTK rover tells you where it is
within 1 mm + 1ppm of distance from base.
http://www.xyht.com/ has regular features on the latest GPS survey gear.
You might be able to convince the local survey equipment rental house to
come out and demo the gear (or give you a good price on a rental)
Or, why not just do the survey optically (!) - none of this new fangled
GPS stuff. Rod, level, theodolite. If Everest could do it in the 19th
century in India, you can do it too.
If you can find a couple benchmarks to work from, you can get accuracy of
1 part in 1000 with a decent 200 foot tape measure and something to sight
with (a cheap laser level at night works pretty good to keep your line
straight). You're doing a series of triangles - SSS completely defines it,
so no angles need be measured.
With decent survey gear 1 part in 10,000 or so is straightforward.
1 ppm is hot stuff with conventional optical gear - you're going to be
making multiple measurements, compensating for refraction, etc. It's like
GPS at 10cm accuracy - lots of things cause errors of that magnitude.
A nice theodolite (like a Wild T2) is readable to 1 second of arc. That's
about 5 microradian. At 100 meters, the horizontal uncertainty would be
0.5mm. Yeah, not quite 1ppm, although you could probably do multiple
setups and average in on 1ppm.
Of course, you'll then need to go out and get a decent tripod, a rod and
target, and a rod person to wave the rod, etc.
But another poster did comment on "why not use the telescope" you could
precision point to a series of stars and calculate using celestial nav
where you are. Although, that might be painful to the 1 meter sort of
accuracy - the "tables" probably don't really account for deviations from
ellipsoid and so forth.
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Peter Monta
2018-04-26 04:43:47 UTC
Permalink
Post by jimlux
But another poster did comment on "why not use the telescope" you could
precision point to a series of stars and calculate using celestial nav
where you are. Although, that might be painful to the 1 meter sort of
accuracy - the "tables" probably don't really account for deviations from
ellipsoid and so forth.
I took a shot at this recently, using the optical signal available from
GPS, Project Echo style:

http://fer3.com/arc/m2.aspx/Navigating-with-GPS-optically-PeterMonta-jan-2018-g41217

It would be difficult to get to 0.3 meter, though. More like 15 meter
single shot, maybe 5 meter with averaging.

As the other responses point out, this is routine for GNSS surveying. A
few hours of dual-frequency GPS data is enough for accuracy of a few
centimeters. If reference stations such as CORS are available, the "rapid
static" solvers cut the needed session time to 20 or 30 minutes. Set up a
reference mark in a clear area, get its position, then use a total station
to do optical ties to other local marks like the telescope mount.

Cheers,
Peter
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Peter Monta
2018-04-26 05:16:13 UTC
Permalink
Hi Tom,
Post by Tom Van Baak
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?
I suspect just L1 would be fine in areas with dense CORS. I have not tried
it, but how about this ultra-cheap strategy:

1. obtain L1 observables with a cheap board and cheap patch antenna;
convert to RINEX
2. synthesize fake L2 data, using nominal iono conditions, and add it to
the RINEX
3. submit to NOAA's rapid static solver, OPUS-RS, which currently accepts
only dual-frequency data
4. examine the quality report from OPUS-RS to see if the ambiguities were
reliably resolved

But this is a bit of a dicey science project; I'd suggest that the
researcher borrow a survey receiver for a few days (mild learning curve for
the online solver tools) or hire a surveyor (no learning curve).

Cheers,
Peter
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jimlux
2018-04-26 13:03:57 UTC
Permalink
Post by Peter Monta
But this is a bit of a dicey science project; I'd suggest that the
researcher borrow a survey receiver for a few days (mild learning curve for
the online solver tools) or hire a surveyor (no learning curve).
If anyone knows a student at any of the following colleges who would be
interested in doing this, I just got a (small) bucket of money to spend
on it, but I have to get the details turned in today.

(actually any sort of time-nuts project, if it can be done for around
$20-30k to the institution, is fine).

Has to be one of those schools, and I need a contact name to call to set
up the details.


Florida A&M
Howard University
Morgan State University
North Carolina Central University
Southern University
Tennessee State University
Tuskegee University-College of Engineering
UC Riverside
University of Nevada Las Vegas (UNLV)
The University of Texas at El Paso


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Bob kb8tq
2018-04-26 16:20:05 UTC
Permalink
Hi

Having once been very much involved in research grants and all the math that goes in-between
the “zero pay labor” and the amount billed to on high ….. it can be pretty amazing just how little
you can get done for $20K using free labor. :)

====

Do software projects count? An analysis library in C to look at phase data ( more or less the guts
of Stable-32) certainly comes to mind. There are a lot of lumps and bumps trying to deal with the
RINEX outputs from gps modules. We have talked about a “pps output “ module for NTP ….

Lots to do …..

Bob
Post by Peter Monta
But this is a bit of a dicey science project; I'd suggest that the
researcher borrow a survey receiver for a few days (mild learning curve for
the online solver tools) or hire a surveyor (no learning curve).
If anyone knows a student at any of the following colleges who would be interested in doing this, I just got a (small) bucket of money to spend on it, but I have to get the details turned in today.
(actually any sort of time-nuts project, if it can be done for around $20-30k to the institution, is fine).
Has to be one of those schools, and I need a contact name to call to set up the details.
Florida A&M
Howard University
Morgan State University
North Carolina Central University
Southern University
Tennessee State University
Tuskegee University-College of Engineering
UC Riverside
University of Nevada Las Vegas (UNLV)
The University of Texas at El Paso
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Ole Petter Ronningen
2018-04-26 09:11:46 UTC
Permalink
Hi

I just ran a quick test - a Ublox 6T was configured to output the RXM-RAW
messages every second and logging for some 14 hours using U-Center. The
.ubx-file was converted to RINEX using teqc.exe, and uplaoded to NrCAN PPP.
NrCAN PPP will process single frequency observations and correct using
ionospheric maps I *believe*. (If I am wrong, ignore this post!)

I also continously log observations from a Trimble NetRS dual frequency GPS
receiver, hooked up to the same antenna. I trust the PPP-calculated
position accuracy of this receiver to within low double digits to high
single digit millimeters.

(For comparison, the report from NrCAN gives a 95% error ellipse on the
UBlox as semi-major: 2.494dm, semi-minor: 1.760dm. The corresponding
numbers for the NetRS is semi-major: 1.245cm, semi-minor: 0.760cm - the
reports are usually below 10 mm in both axis. Note difference in units.)

Comparing the calculated ECEF coordinates from the ppp-results using
Pythagoras gives me a distance of 76 cm - 53 cm if we simply ignore height.

This is with a survey grade antenna in a good location. It might be
possible to shrink this to 30 cm and still have confidence in the results,
but I think it would not be easy. I would guess a lot more data would be
required, and it is also possible that delaying processing until more
accurate ionospheric maps are available could help.

I will reprocess in a couple of days and see if theres much of a difference.

Ole
Post by Tom Van Baak
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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Joseph Gwinn
2018-04-26 13:57:06 UTC
Permalink
time-nuts Digest, Vol 165, Issue 50
Message: 3
Date: Wed, 25 Apr 2018 10:19:38 -0500
Subject: Re: [time-nuts] nuts about position
Content-Type: text/plain; charset="UTF-8"
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".
It will have been using carrier phase only, not the L2 modulation
(which is encrypted). Although one can do correlation on the L2
modulation from a given satellite in common view as well.

Joe Gwinn
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Martin VE3OAT
2018-04-27 14:03:28 UTC
Permalink
Hi, Pat,

Oh boy, sounds like quite the place! A tour would be wonderful, but I
live even further away than most of you (eastern Ontario, Canada).
Hobbies are time-frequency, astronomy and ham radio. Hat Creek sounds
like heaven so I hope you get lots of takers. Good luck with the
tour. Post more pictures!

73,
... Martin VE3OAT


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Mark Sims
2018-04-30 20:36:33 UTC
Permalink
Coincidentally, yesterday I tweaked up Lady Heather's Ublox code to enable all of the necessary raw data messages. Heather also enables the raw messages from Trimble TSIP speaking receivers, the NVS CSM24 receiver, and the Furuno GT87 receiver (if baud rate is >=115200).

Heather can write a raw data capture file (/dr=filename on the command line or WY from the keyboard). You should be able to convert those raw capture files to RINEX and then post-process those.
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Bob kb8tq
2018-04-30 23:44:20 UTC
Permalink
Hi

You mean that LH does not translate the data to the correct format *and* submit it for post processing ?????

There *is* a lot of data when you turn all this stuff on. If you can get above 115K baud, it’s well worth it.

=====

One important qualifier to re-state. L1 post processing is very dependent on the distance to an “open” source
of correction data. The spacing of those sites over the US is highly variable. If you get outside the US it is very
much a “that depends” sort of thing. Some countries apparently don’t have the same sort of open site network
that we have in the US.

Bob
Post by Mark Sims
Coincidentally, yesterday I tweaked up Lady Heather's Ublox code to enable all of the necessary raw data messages. Heather also enables the raw messages from Trimble TSIP speaking receivers, the NVS CSM24 receiver, and the Furuno GT87 receiver (if baud rate is >=115200).
Heather can write a raw data capture file (/dr=filename on the command line or WY from the keyboard). You should be able to convert those raw capture files to RINEX and then post-process those.
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Mark Sims
2018-05-01 02:48:17 UTC
Permalink
I once spent way too much time trying to get Heather to spit out a RINEX file from a Thunderbolt. I could never get any of the post-processors to accept it. The Thunderbolt's raw data needs to somehow be tweaked to be compatible and I didn't really know what I was doing.

A LEA-6T seems to be able to cope with the data stream at it's default 9600 baud. I just tried a NEO-8N and it drops packets, etc. Even weirder, it does not output any of the requested packets that might be flooding the port, but still drops packets.


-----------------------
Post by Bob kb8tq
You mean that LH does not translate the data to the correct format *and* submit it for post processing ?????
There *is* a lot of data when you turn all this stuff on. If you can get above 115K baud, it’s well worth it.
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Gary E. Miller
2018-05-01 03:05:18 UTC
Permalink
Yo Mark!

On Tue, 1 May 2018 02:48:17 +0000
Post by Mark Sims
A LEA-6T seems to be able to cope with the data stream at it's
default 9600 baud. I just tried a NEO-8N and it drops packets,
I think heather is parsing the UBX_RAW_RATE messages for the
raw GPS meansurements. The LEA-6T allows UBX_RAW_RATE, but the
NEO-M8N does not.

RGDS
GARY
---------------------------------------------------------------------------
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***@rellim.com Tel:+1 541 382 8588

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"If you can’t measure it, you can’t improve it." - Lord Kelvin
Bob kb8tq
2018-05-01 13:12:05 UTC
Permalink
Hi

The “drops stuff” problem is exactly what I saw trying to run at lower baud rates.
The port is *not* full of data, there’s plenty of time to get it all out at a lower baud
rate. For some reason (buffers maybe) these modules start dropping data *way*
earlier than you would think they should.

Bob
Post by Mark Sims
I once spent way too much time trying to get Heather to spit out a RINEX file from a Thunderbolt. I could never get any of the post-processors to accept it. The Thunderbolt's raw data needs to somehow be tweaked to be compatible and I didn't really know what I was doing.
A LEA-6T seems to be able to cope with the data stream at it's default 9600 baud. I just tried a NEO-8N and it drops packets, etc. Even weirder, it does not output any of the requested packets that might be flooding the port, but still drops packets.
-----------------------
Post by Bob kb8tq
You mean that LH does not translate the data to the correct format *and* submit it for post processing ?????
There *is* a lot of data when you turn all this stuff on. If you can get above 115K baud, it’s well worth it.
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Mark Sims
2018-05-01 04:32:02 UTC
Permalink
Heather now requests the RAW and RAWX messages... those output carrier phase, doppler, and pseudo ranges. The M8N does not support either, but the M8T supports RAWX.

Heather now requests the SFRB and SFRBX messages... those output the satellite navigation messages. All the M8's output SFRBX.

I cranked up the M8N baud rate to 115200 and the receiver can handle all the various raw messages.... But the bugaboo is requesting the TRK-MEAS and TRK-SFRBX messages. The messages are not officially supported, Ublox forbids talking about them on their forums... they might even dispatch Ninja assassins if you talk about them. If you request those messages on the M8N very bad things seem to happen... you start receiving messages 0x27-0x00 with a length of either 68 bytes or around 1300-1400 bytes. Whatever 0x27-0x00 is, nobody's talking... The 0x27 message group is for security features like chip serial numbers.

I have an M8T on the way from Germany...

------------------
Post by Gary E. Miller
I think heather is parsing the UBX_RAW_RATE messages for the
raw GPS meansurements. The LEA-6T allows UBX_RAW_RATE, but the
NEO-M8N does not.
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Mark Sims
2018-05-01 23:40:21 UTC
Permalink
I added some debug log info that shows how many bytes the receiver sent between time messages. The LEA-6T sends around 500-600 bytes every second. That fits easily into 9600 baud. The M8N tracking all sats and with all the raw messages enabled spews around 4000 bytes. That would require 57,600 baud.

It looks like M8N's with standard firmware are not suitable for precise positioning. They do not output the required RAW data messages:
https://rtklibexplorer.wordpress.com/2017/06/07/newest-u-blox-m8n-receivers-not-usable-with-rtklib/

Various GPS receivers handle transmit buffer overflows in different ways... including various combinations of dropping messages, garbling data, or crashing. Most receivers seem to have transmit/receiver buffers in the 1000 byte range... some are smaller, some are larger.
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