Discussion:
nuts about position (cheap receiver)
(too old to reply)
Mark Sims
2018-05-02 02:00:15 UTC
Permalink
There are some sellers on Ebay LEA-5T receivers on Ebay for cheap. They are pin and layout compatible with the Trimble Resolution-T devices. I bought a couple from this guy ($24 each) and they do output the RAW and SFRB messages. He also has LEA-4T and Trimble boards. There are also other sellers that are more expensive... search for LEA-5T

https://www.ebay.com/itm/Ublox-LEA-5T-GPS-MODULE-BOARD/253584793155?hash=item3b0ad4de43:g:6CEAAOSwEZdZ7Z-7

I have not tried to post-process the data yet. I currently have Heather doing a raw data capture...
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Mark Sims
2018-05-02 21:54:47 UTC
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Well, I processed the Lady Heather .raw capture file from the $24 LEA-5T through RTKCONV and submitted it to CSRS-PPP and it worked. Using the less precise instant orbits it says the 95% sigma errors are: lat: 0.169m lon:0.148m alt: 0.399m

My antenna is that Chinese L1/L2/Glonass/etc antenna from ebay. I'll re-submit the data next week and see how it changes.

Also, I now sort-of have Heather outputting a RINEX 3.02 format .OBS file.

Oh, and Bob... Heather can run an external program at a given time or after a specified interval, so could be set up to automatically submit the file... you lazy bastard ;-)
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Tim Lister
2018-05-02 22:16:16 UTC
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Post by Mark Sims
Well, I processed the Lady Heather .raw capture file from the $24 LEA-5T through RTKCONV and submitted it to CSRS-PPP and it worked. Using the less precise instant orbits it says the 95% sigma errors are: lat: 0.169m lon:0.148m alt: 0.399m
My antenna is that Chinese L1/L2/Glonass/etc antenna from ebay. I'll re-submit the data next week and see how it changes.
Was the solution using the NRCan hourly's or the IGS Rapid products ?
(It should say in the email response or the <foo>.sum file: the
'Satellite orbits/clocks' lines seem to have 'emu', 'emr' or 'igs' for
the NRCan hourly/UltraRapid, Rapid and Final solutions respectively).
Submittals less than a day after the observations in the RINEX file
seem to result in the use of the Hourly/UltraRapids solutions.

Cheers,
Tim
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Mark Sims
2018-05-03 00:07:23 UTC
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For the orbits is says "Precise", so maybe not even the hourly ones. I could not find any mention of emu, emr, or igs.

Heather can now spit out Rinex 3.02 files (at least for GPS/SBAS sats). I am currently feeding Heather the .raw capture file I sent to Canada and outputting a RINEX .OBS file. I'll send that off to them and see if there is any difference in the results from the one from RTKCONV. The RTKCONV processed values for pseudo ranges and carrier phase values seems to have been tweaked from what the receiver sent... they differ by a fractional amount.

---------------------
Post by Tim Lister
Was the solution using the NRCan hourly's or the IGS Rapid products ?
(It should say in the email response or the <foo>.sum file: the
'Satellite orbits/clocks' lines seem to have 'emu', 'emr' or 'igs' for
the NRCan hourly/UltraRapid, Rapid and Final solutions respectively).
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Mark Sims
2018-05-03 01:40:44 UTC
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Grrrr... Canada lives in the dark ages and does not accept RINEX version 3... I'm now trying Australia...

Version 3 is cleaner and easier to write than Version 2...
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Gabs Ricalde
2018-05-03 03:35:00 UTC
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Post by Mark Sims
Grrrr... Canada lives in the dark ages and does not accept RINEX version 3... I'm now trying Australia...
Version 3 is cleaner and easier to write than Version 2...
RTKLIB's RTKCONV can convert between RINEX versions.
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Mark Sims
2018-05-03 03:26:30 UTC
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I tried submitting Version 3 files to several services... none support Version 3! Heather now creates the uglier/less readable Version 2.10 RINEX,
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Mark Sims
2018-05-03 04:36:32 UTC
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The goal is to make it as simple as possible and have Heather do all the receiver configuring, data capture, and RINEX making... with none of that tedious mucking about in RTKLIB Currently all I have to do is fire up Heather and tell it to write a log file with the .obs extension.

------------------
Post by Gabs Ricalde
RTKLIB's RTKCONV can convert between RINEX versions.
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Chris Caudle
2018-05-03 14:17:19 UTC
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Post by Mark Sims
have Heather do all the receiver configuring, data
capture, and RINEX making...
I have been following along with the update messages, and this seems like
really cool improvements to the underlying infrastructure pieces that a
lot of us use (Lady Heather, support for more GPS modules, etc.), but I
am having trouble putting all the pieces together.

Having submitted the files to some post-processing server, do you only get
back information showing your position to some small number of
centimeters, or does it send back a stream of values showing the
corrections to the full position + time equations at each reading?
Can you use this data to go back to, for example, a stream of timestamps
and add a correction factor to the timestamps to get improved time
accuracy on historical data?
--
Chris Caudle




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Bob kb8tq
2018-05-03 15:09:05 UTC
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Hi

The sites are aimed at improving position information. To the degree that having an
accurate location for your antenna improves timing, simply doing that is a step forward
for your GPSDO.

Most sites also will give you information that shows the timing solution at a given point
in time. To the degree that you can connect that to prior data it could be useful. There
are more than a few steps involved in getting this to work.

Bob
Post by Chris Caudle
Post by Mark Sims
have Heather do all the receiver configuring, data
capture, and RINEX making...
I have been following along with the update messages, and this seems like
really cool improvements to the underlying infrastructure pieces that a
lot of us use (Lady Heather, support for more GPS modules, etc.), but I
am having trouble putting all the pieces together.
Having submitted the files to some post-processing server, do you only get
back information showing your position to some small number of
centimeters, or does it send back a stream of values showing the
corrections to the full position + time equations at each reading?
Can you use this data to go back to, for example, a stream of timestamps
and add a correction factor to the timestamps to get improved time
accuracy on historical data?
--
Chris Caudle
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jimlux
2018-05-03 15:34:52 UTC
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Post by Bob kb8tq
Hi
The sites are aimed at improving position information. To the degree that having an
accurate location for your antenna improves timing, simply doing that is a step forward
for your GPSDO.
Most sites also will give you information that shows the timing solution at a given point
in time. To the degree that you can connect that to prior data it could be useful. There
are more than a few steps involved in getting this to work.
The JPL processing chain gives not only more accurate positions vs time,
but also estimates of clock error vs time, if that's in the data stream
being processed.
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Artek Manuals
2018-05-03 15:12:44 UTC
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To further Chris' question if I took data say on the same day every year
can I measure which way my tectonic plate is moving and how far?

-DC
Post by Chris Caudle
Post by Mark Sims
have Heather do all the receiver configuring, data
capture, and RINEX making...
I have been following along with the update messages, and this seems like
really cool improvements to the underlying infrastructure pieces that a
lot of us use (Lady Heather, support for more GPS modules, etc.), but I
am having trouble putting all the pieces together.
Having submitted the files to some post-processing server, do you only get
back information showing your position to some small number of
centimeters, or does it send back a stream of values showing the
corrections to the full position + time equations at each reading?
Can you use this data to go back to, for example, a stream of timestamps
and add a correction factor to the timestamps to get improved time
accuracy on historical data?
--
Dave
***@ArtekManuals.com
www.ArtekManuals.com


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Bob kb8tq
2018-05-03 15:28:38 UTC
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Hi

If you have a very good survey grade receiver and take a long enough data set, yes you can
watch your location drift in some parts of the world. In most locations, fixes a few years apart
would be a better bet.

Indeed this does get a bit far from the world of timing …… The distances involved are nasty
small. Even for the location of your telescope when doing astronomical timing observations,
they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” ….

Bob
To further Chris' question if I took data say on the same day every year can I measure which way my tectonic plate is moving and how far?
-DC
Post by Chris Caudle
Post by Mark Sims
have Heather do all the receiver configuring, data
capture, and RINEX making...
I have been following along with the update messages, and this seems like
really cool improvements to the underlying infrastructure pieces that a
lot of us use (Lady Heather, support for more GPS modules, etc.), but I
am having trouble putting all the pieces together.
Having submitted the files to some post-processing server, do you only get
back information showing your position to some small number of
centimeters, or does it send back a stream of values showing the
corrections to the full position + time equations at each reading?
Can you use this data to go back to, for example, a stream of timestamps
and add a correction factor to the timestamps to get improved time
accuracy on historical data?
--
Dave
www.ArtekManuals.com
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jimlux
2018-05-03 15:36:18 UTC
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Post by Bob kb8tq
Hi
If you have a very good survey grade receiver and take a long enough data set, yes you can
watch your location drift in some parts of the world. In most locations, fixes a few years apart
would be a better bet.
Indeed this does get a bit far from the world of timing …… The distances involved are nasty
small. Even for the location of your telescope when doing astronomical timing observations,
they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” ….
Bob
Unless you live on a plate boundary and have to keep repairing your
fences and foundations <grin>

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jimlux
2018-05-03 15:38:37 UTC
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Post by Bob kb8tq
Hi
If you have a very good survey grade receiver and take a long enough data set, yes you can
watch your location drift in some parts of the world. In most locations, fixes a few years apart
would be a better bet.
Indeed this does get a bit far from the world of timing …… The distances involved are nasty
small. Even for the location of your telescope when doing astronomical timing observations,
they are unlikely to matter on a yearly basis. At some point the error is “to small to matter” ….
Bob
Hit send too quick..

But more realistically, this is kind of a time-nutty sort of goal - to
be able to make measurements to a precision where you can match your
measurements to a nearby geodetic station with "official" measurements.

All the usual time measurement with GPS issues come into it - multipath,
the diurnal variations, solid earth tides.

It's what everyone says - getting to meters or 10s of ns - easy -
getting to tenths of ns or cm, significantly harder.
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Mark Sims
2018-05-03 07:56:56 UTC
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Woohoo! Success! I sent a RINEX 2.10 formatted .obs file generated by Heather from a Ublox 5 to Canada for post-processing. The results matched those from RTKLIB processing to within 1mm. Oh, and on noth cases the post-processing used the "emu" orbit info.

I haven't heard back from Australia, but I think the file that I sent down under has some duplicate data block errors.
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Bob kb8tq
2018-05-03 13:27:49 UTC
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Hi

Thank goodness it now is almost all self contained. Typing three or for lines of a script is *so* last century :)

Sounds very cool !!!!!!

LH continues to do amazing things. She is an impressive lady. Do you ever have time to sleep?

My guess is that some sort of write up for doing the submittal to each of the “likely victim” agencies will be
needed. Then of course there is the data reduction and plotting on the returned file …… hmmm …… :)

Bob
Post by Mark Sims
Woohoo! Success! I sent a RINEX 2.10 formatted .obs file generated by Heather from a Ublox 5 to Canada for post-processing. The results matched those from RTKLIB processing to within 1mm. Oh, and on noth cases the post-processing used the "emu" orbit info.
I haven't heard back from Australia, but I think the file that I sent down under has some duplicate data block errors.
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Mark Sims
2018-05-03 16:26:35 UTC
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To give an idea about the possible improvement in antenna location available by post-processing the data, I first did a 2 hour self-survey and that put the receiver into position hold mode. Then I collected RINEX data for 16 hours. The post-processed lat/lon/alt values differed around 1/1/3 meters better than the self-survey values (with estimated error ellipses of 0.17/0.15/0.4 meters). Those results were with the "ultra rapid" orbits. It will be interesting to see what they look like when the final precise orbits are available in a couple of weeks.

I also need to see how those values compare to Lady Heather's precision survey results.
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Ole Petter Ronningen
2018-05-03 17:03:19 UTC
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In my experience, there is little difference between the Final and Rapid,
which will be out just about now (for yesterdays observations)

Ole
Post by Mark Sims
To give an idea about the possible improvement in antenna location
available by post-processing the data, I first did a 2 hour self-survey
and that put the receiver into position hold mode. Then I collected RINEX
data for 16 hours. The post-processed lat/lon/alt values differed around
1/1/3 meters better than the self-survey values (with estimated error
ellipses of 0.17/0.15/0.4 meters). Those results were with the "ultra
rapid" orbits. It will be interesting to see what they look like when the
final precise orbits are available in a couple of weeks.
I also need to see how those values compare to Lady Heather's precision survey results.
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J Grizzard
2018-05-03 17:13:47 UTC
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Post by Mark Sims
Those results were with the "ultra rapid" orbits. It will be interesting to see what they look like when the final precise orbits are available in a couple of weeks.
I also need to see how those values compare to Lady Heather's precision survey results.
FWIW, a dual-frequency PPP run I did late last year has the following
uncertainties, when processed with the various IGS precision
ephemerides, via AUSPOS:

                longitude           latitude          altitude
IGS UltraRapid     0.004m 0.003m            0.013m
IGS Rapid          0.004m 0.003m            0.012m
IGS Final          0.004m             0.003m 0.012m

The computed ECEF coordinates change by 0.003m(X) and 0.001m(Z) between
UltraRapid and Final.

...so really not much of a difference between UltraRapid and Final, at
least for a dual-frequency survey at my location.

*digs through old stuff*

Okay, found a single-frequency survey from mid-last-year, processed by CSRS:

                longitude           latitude          altitude
NRCan Rapid        0.103m            0.121m 0.253m
IGS Final          0.103m             0.121m 0.252m

...not much difference there, either.

Both of these were with a roof-mounted antenna and a good skyview,
running 24 hours. The first was one measurement every 15 seconds, the
latter one measurement per second. (I think for these purposes, one
measurement every 15 seconds is more than sufficient and makes the files
process *so* much faster).

-j
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