Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

Hi Springer.Have fun and your questions stimulated a good discussion and 
ideas.If you are collecting gps data on the clock, I would seriously consider 
installing a ground plane on your range pole. This will eliminate zingers and 
you can reduce your observation time. A electrical junction box cover works 
well.Waas currently is good to 0.9 m horizontal and 1.3 m vertical 95% of the 
time. It helps but is not a stand alone solution for high precision work.Kirk 
SchmidtSent from my Galaxy
 Original message From: Springfield Harrison 
 Date: 2021-03-10  4:30 a.m.  (GMT-04:00) To: Kirk 
Schmidt , qgis-user@lists.osgeo.org Subject: Re: 
[Qgis-user] Trimble GeoXT 2005 Accuracy Hi Kirk,OK, I'll rule out the PPP for 
now, although it doesn't seem to be practical for production mapping anyway.I 
think my antennas are probably OK, none of them have a ground plane, not 
practical for field mapping.  I've only seen them in geodetic applications.  Of 
course, the aircraft installation is free of multipath except while on the 
ground.  Longer observing periods should minimize the impact of multipath 
zingers.The tight clustering of the GeoXT points in Map A doesn't smell of 
multipath to me.Earlier you noted the possibility of antenna shielding by the 
operator.  With that in mind, I use a tripod or a range pole with the antenna 
above head height.  WAAS is actually quite accurate, good for certain (lower 
order?) precision approaches.I'm still digesting all this helpful feedback and 
will work on a summary shortly.  Thanks again . . . .-Cheers, SpringOn 
09/Mar/2021 12:14, Kirk Schmidt wrote:> Hi Springfield:>> PPP requires long 
observation times in the order of hours and > therefore a new field survey.  I 
would try post processing from a high > precision site with your existing 
data.>> Another issue may be the aviation antennae you mentioned.  These are > 
usually mounted on the top of a fuselage and therefore the aluminum > acts as a 
ground plane to effectively filter out multipath.  If you > use a metal disk or 
plate and a ground plane on your antennae and > mount it on a tripod, you may 
find you end up with better results.  > You will notice survey grade antennae's 
have a large diameter plastic > case since the contain an internal 10 cm metal 
disk.>> Kirk Schmidt>> On 3/9/2021 1:36 PM, Springfield Harrison wrote:>> Hello 
Garth,>>>> Thanks very much for that reference.  I have used the service in the 
>> past.>>>> I'm in the middle of other work but may try to re-process some Map 
A >> files using PPP to see what changes.>>>> Your work sounds more like 
surveying than mapping, interesting.>>>> I do use the GPS reception planning 
tools but SV availability is >> certainly better than in the early days.>>>> 
Thanks again . . . .>>>> ->> Cheers, Spring>>>>>>>> On 09/Mar/2021 09:01, 
Garth Fletcher wrote:>>> Nicolas Cadieux wrote:>>>> Kirk could be on the right 
track.  You could try PPP using this >>>> site.  You will need to create a user 
name and password.  Then, you >>>> upload the Rinex file. I am 99% sure you can 
process point from >>>> outside of Canada. >>>>>> I routinely use CSRS PPP to 
post process RINEX files from Southern New>>> Hampshire (43°N, 72°W).>>>>>> 
Using an iGage iG3s (L1/L2 dual frequency, GPS + GLONASS) recording at>>> 5 
second epochs in forested areas, from post processing I get>>>  30 minute 
recordings, 95% error ellipses < 1 meter>>>  10 hour recordings,   95% error 
ellipses < 2 cm>>>>>> CSRS-PPP site is>>> 
<https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php?locale=en>>>> enter 
your email address>>> select Static and which NAD 83 epoch you want, or ITRF>>> 
Submit a RINEX file (.zip compressing the file is encouraged)>>> they will 
email back a detailed report>>>>>> You can submit for 1 of 3 levels of post 
processing>>>  ultra-rapid : submit > 90 minutes after end of recording>>>  
rapid: submit > 24 hours after end of recording>>>  final:  submit ~ 3 weeks 
after end of recording>>>>>> Major part of corrections are in ultra-rapid, the 
higher levels provide>>> further refinements.>>>>>>>>> FYI: Trimble provides 
occupation planning aids at>>> <https://www.gnssplanning.com/#/charts>>>> just 
enter your location and date and it shows you the DOP as>>> a function of the 
hour of day.>>>>>> Cordially,>> 
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hi Kirk,

OK, I'll rule out the PPP for now, although it doesn't seem to be 
practical for production mapping anyway.


I think my antennas are probably OK, none of them have a ground plane, 
not practical for field mapping.  I've only seen them in geodetic 
applications.  Of course, the aircraft installation is free of multipath 
except while on the ground.  Longer observing periods should minimize 
the impact of multipath zingers.


The tight clustering of the GeoXT points in Map A doesn't smell of 
multipath to me.


Earlier you noted the possibility of antenna shielding by the operator.  
With that in mind, I use a tripod or a range pole with the antenna above 
head height.  WAAS is actually quite accurate, good for certain (lower 
order?) precision approaches.


I'm still digesting all this helpful feedback and will work on a summary 
shortly.  Thanks again . . . .


-
Cheers, Spring



On 09/Mar/2021 12:14, Kirk Schmidt wrote:

Hi Springfield:

PPP requires long observation times in the order of hours and 
therefore a new field survey.  I would try post processing from a high 
precision site with your existing data.


Another issue may be the aviation antennae you mentioned.  These are 
usually mounted on the top of a fuselage and therefore the aluminum 
acts as a ground plane to effectively filter out multipath.  If you 
use a metal disk or plate and a ground plane on your antennae and 
mount it on a tripod, you may find you end up with better results.  
You will notice survey grade antennae's have a large diameter plastic 
case since the contain an internal 10 cm metal disk.


Kirk Schmidt

On 3/9/2021 1:36 PM, Springfield Harrison wrote:

Hello Garth,

Thanks very much for that reference.  I have used the service in the 
past.


I'm in the middle of other work but may try to re-process some Map A 
files using PPP to see what changes.


Your work sounds more like surveying than mapping, interesting.

I do use the GPS reception planning tools but SV availability is 
certainly better than in the early days.


Thanks again . . . .

-
Cheers, Spring



On 09/Mar/2021 09:01, Garth Fletcher wrote:

Nicolas Cadieux wrote:
Kirk could be on the right track.  You could try PPP using this 
site.  You will need to create a user name and password.  Then, you 
upload the Rinex file. I am 99% sure you can process point from 
outside of Canada. 


I routinely use CSRS PPP to post process RINEX files from Southern New
Hampshire (43°N, 72°W).

Using an iGage iG3s (L1/L2 dual frequency, GPS + GLONASS) recording at
5 second epochs in forested areas, from post processing I get
 30 minute recordings, 95% error ellipses < 1 meter
 10 hour recordings,   95% error ellipses < 2 cm

CSRS-PPP site is

enter your email address
select Static and which NAD 83 epoch you want, or ITRF
Submit a RINEX file (.zip compressing the file is encouraged)
they will email back a detailed report

You can submit for 1 of 3 levels of post processing
 ultra-rapid : submit > 90 minutes after end of recording
 rapid: submit > 24 hours after end of recording
 final:  submit ~ 3 weeks after end of recording

Major part of corrections are in ultra-rapid, the higher levels provide
further refinements.


FYI: Trimble provides occupation planning aids at

just enter your location and date and it shows you the DOP as
a function of the hour of day.

Cordially,

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hi Kirk,

Right, that could be the case although the GeoXT is not set up for RTCM, 
only WAAS. The ProXR has an RTCM antenna though. Too many variables!


But I see that WAAS is fairly accurate:

"The WAAS specification requires it to provide a position accuracy of 
7.6 metres (25 ft) or less (for both lateral and vertical measurements), 
at least 95% of the time.^[2] 
<https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System#cite_note-WASSspec-2> 
Actual performance measurements of the system at specific locations have 
shown it typically provides better than 1.0 metre (3 ft 3 in) laterally 
and 1.5 metres (4 ft 11 in) vertically throughout most of thecontiguous 
United States 
<https://en.wikipedia.org/wiki/Contiguous_United_States>and large parts 
ofCanada <https://en.wikipedia.org/wiki/Canada>andAlaska 
<https://en.wikipedia.org/wiki/Alaska>.^[3] 
<https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System#cite_note-WAAS_NSTB_PAN_Report_Jul06-3> 
With these results, WAAS is capable of achieving the required Category I 
precision approach accuracy of 16 metres (52 ft) laterally and 4.0 
metres (13.1 ft) vertically.^[4] 
<https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System#cite_note-faa.gov-4>" 
-Wikipedia


-
Cheers, Spring



On 09/Mar/2021 04:32, kirk wrote:

Hi Springer

I just looked up the marine beacon specs and they are designed for 10m 
accuracy. This may explain why your non dgps data is closer to your 
survey corner.




Sent from my Galaxy


 Original message 
From: Springfield Harrison 
Date: 2021-03-08 3:17 p.m. (GMT-04:00)
To: Nicolas Cadieux 
Cc: kirk , Jorge Gustavo Rocha 
, qgis-user@lists.osgeo.org, Greg Troxel 
, Dan <19dm...@gmail.com>

Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

I'm resending this without the map as there is a size limit. The 
moderator may let it through, I hope . . . .


Hi Nicolas, thanks for your observations.  I'll try to answer your 
questions, please see the attached map, especially Map A:


Note that my previous email contained information for Map B; Map A is 
based on the Municipal Cadastre (NAD83 UTM zone 10N) and illustrates 
the problem as well. Other locations based on Provincial Monuments 
and/or the Municipal cadastre (not illustrated here) have yielded 
similar results.


 1. How many “known” points have you tested?
 1. 2 in this case, Maps A and B
 2. Also several other locations with similar results
 2. How where those point position calculated.
 1. From the Municipal cadastre, visible in Map A
 3. Make sure the coordinates are in the right CRS
 1. NAD 83 UTM 10N used throught.  See workflow in previous email
 4. When converting from the monument’s CRS to NAD83 UTM zone 10N, are
you using the correct grid files?
 1. [No monuments in this example] These were brought into QGIS
from the Municipal GCM database CSV (NAD83(CSRS)
3.0.0.BC.1.CRD) and reprojected by QGIS to EPSG:26910 - NAD83
/ UTM zone 10N
 2. Presumably QGIS would choose the correct grid files
 3. Municipal Cadastre is NAD83 UTM zone 10N
 5. Find a geodesic point that is in the middle of a field or on the
side of a highway with no obstacles.
 1. Map A is open sky
 6. Make sur your observations will be done when the constellation is
well distributed in the sky
 1. As you probably know, TerraSync provides for PDOP, HDOP, SNR
and Horizon masks to preclude collecting poor quality
positions. These were set towards the "Precision" end of the
scale
 7. What post processing techniques are you using? How far is the base
station from your unit?
 1. Real time was SBAS or RTCM; Post processing using the
Pathfinder Office differential correction engine, baseline
about 30 km
 8. How long are the observations? Have you tried other methods of
post processing like PPP?
 1. Logging interval is 5 sec; 33 to 2037 positions per point
 2. Did not use PPP. This is a test of mapping best practices, not
geodesy
 9. Have you contacted Trimble?
 1. Yes, no response
10. Have you looked on there site to see if there is a software update
(firmware) for the unit or the post processing software?
 1. Yes, receiver firmware is the latest, PFO and Terrasync are
older but compatible

Thanks Nicolas. If I have missed something, I hope someone can point 
it out, I've tried to cover all the bases based on my training and 
experience.


-
Cheers, Spring



On 08/Mar/2021 06:40, Nicolas Cadieux wrote:

Hi Harrison,

How many “known” points have you tested? How where those point 
position calculated. They could be off.  If you are using state 
geodesic monuments, try to find the documented precision of the 
monument. States have different types of monuments, some are very old 
and have different standards.  Make sure the geodesic point is not 
the problem.  M

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Kirk Schmidt]

Hi Springfield:

PPP requires long observation times in the order of hours and therefore 
a new field survey.  I would try post processing from a high precision 
site with your existing data.


Another issue may be the aviation antennae you mentioned.  These are 
usually mounted on the top of a fuselage and therefore the aluminum acts 
as a ground plane to effectively filter out multipath.  If you use a 
metal disk or plate and a ground plane on your antennae and mount it on 
a tripod, you may find you end up with better results.  You will notice 
survey grade antennae's have a large diameter plastic case since the 
contain an internal 10 cm metal disk.


Kirk Schmidt

On 3/9/2021 1:36 PM, Springfield Harrison wrote:

Hello Garth,

Thanks very much for that reference.  I have used the service in the 
past.


I'm in the middle of other work but may try to re-process some Map A 
files using PPP to see what changes.


Your work sounds more like surveying than mapping, interesting.

I do use the GPS reception planning tools but SV availability is 
certainly better than in the early days.


Thanks again . . . .

-
Cheers, Spring



On 09/Mar/2021 09:01, Garth Fletcher wrote:

Nicolas Cadieux wrote:
Kirk could be on the right track.  You could try PPP using this 
site.  You will need to create a user name and password.  Then, you 
upload the Rinex file.   I am 99% sure you can process point from 
outside of Canada. 


I routinely use CSRS PPP to post process RINEX files from Southern New
Hampshire (43°N, 72°W).

Using an iGage iG3s (L1/L2 dual frequency, GPS + GLONASS) recording at
5 second epochs in forested areas, from post processing I get
 30 minute recordings, 95% error ellipses < 1 meter
 10 hour recordings,   95% error ellipses < 2 cm

CSRS-PPP site is

enter your email address
select Static and which NAD 83 epoch you want, or ITRF
Submit a RINEX file (.zip compressing the file is encouraged)
they will email back a detailed report

You can submit for 1 of 3 levels of post processing
 ultra-rapid : submit > 90 minutes after end of recording
 rapid: submit > 24 hours after end of recording
 final:  submit ~ 3 weeks after end of recording

Major part of corrections are in ultra-rapid, the higher levels provide
further refinements.


FYI: Trimble provides occupation planning aids at

just enter your location and date and it shows you the DOP as
a function of the hour of day.

Cordially,

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--
Kirk Schmidt, MScF, BScF, RPF
General Manager
Nortek Resource Solutions Inc.
RR # 1
Thorburn, NS
B0K 1W0
Tel (902) 922.3607
Email: k...@nortekresources.com
Web: www.nortekresources.com

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hello Garth,

Thanks very much for that reference.  I have used the service in the past.

I'm in the middle of other work but may try to re-process some Map A 
files using PPP to see what changes.


Your work sounds more like surveying than mapping, interesting.

I do use the GPS reception planning tools but SV availability is 
certainly better than in the early days.


Thanks again . . . .

-
Cheers, Spring



On 09/Mar/2021 09:01, Garth Fletcher wrote:

Nicolas Cadieux wrote:
Kirk could be on the right track.  You could try PPP using this 
site.  You will need to create a user name and password.  Then, you 
upload the Rinex file.   I am 99% sure you can process point from 
outside of Canada. 


I routinely use CSRS PPP to post process RINEX files from Southern New
Hampshire (43°N, 72°W).

Using an iGage iG3s (L1/L2 dual frequency, GPS + GLONASS) recording at
5 second epochs in forested areas, from post processing I get
 30 minute recordings, 95% error ellipses < 1 meter
 10 hour recordings,   95% error ellipses < 2 cm

CSRS-PPP site is

enter your email address
select Static and which NAD 83 epoch you want, or ITRF
Submit a RINEX file (.zip compressing the file is encouraged)
they will email back a detailed report

You can submit for 1 of 3 levels of post processing
 ultra-rapid : submit > 90 minutes after end of recording
 rapid: submit > 24 hours after end of recording
 final:  submit ~ 3 weeks after end of recording

Major part of corrections are in ultra-rapid, the higher levels provide
further refinements.


FYI: Trimble provides occupation planning aids at

just enter your location and date and it shows you the DOP as
a function of the hour of day.

Cordially,

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Garth Fletcher]

Nicolas Cadieux wrote:
Kirk could be on the right track.  You could try PPP using this site.  You will need to create a user name and password.  Then, you upload the Rinex file.   I am 99% sure you can process point from outside of Canada.  


I routinely use CSRS PPP to post process RINEX files from Southern New
Hampshire (43°N, 72°W).

Using an iGage iG3s (L1/L2 dual frequency, GPS + GLONASS) recording at
5 second epochs in forested areas, from post processing I get
 30 minute recordings, 95% error ellipses < 1 meter
 10 hour recordings,   95% error ellipses < 2 cm

CSRS-PPP site is

enter your email address
select Static and which NAD 83 epoch you want, or ITRF
Submit a RINEX file (.zip compressing the file is encouraged)
they will email back a detailed report

You can submit for 1 of 3 levels of post processing
 ultra-rapid : submit > 90 minutes after end of recording
 rapid: submit > 24 hours after end of recording
 final:  submit ~ 3 weeks after end of recording

Major part of corrections are in ultra-rapid, the higher levels provide
further refinements.


FYI: Trimble provides occupation planning aids at

just enter your location and date and it shows you the DOP as
a function of the hour of day.

Cordially,
--
Garth Fletcher
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Nicolas Cadieux]

Hi,

Kirk could be on the right track.  You could try PPP using this site.  You will 
need to create a user name and password.  Then, you upload the Rinex file.   I 
am 99% sure you can process point from outside of Canada.  

https://webapp.geod.nrcan.gc.ca/geod/tools-outils/ppp.php?locale=en

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 9 mars 2021 à 07:32, kirk  a écrit :
> 
> 
> Hi Springer
> 
> I just looked up the marine beacon specs and they are designed for 10m 
> accuracy. This may explain why your non dgps data is closer to your survey 
> corner.
> 
> 
> 
> Sent from my Galaxy
> 
> 
>  Original message 
> From: Springfield Harrison 
> Date: 2021-03-08 3:17 p.m. (GMT-04:00)
> To: Nicolas Cadieux 
> Cc: kirk , Jorge Gustavo Rocha , 
> qgis-user@lists.osgeo.org, Greg Troxel , Dan 
> <19dm...@gmail.com>
> Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy
> 
> I'm resending this without the map as there is a size limit. The moderator 
> may let it through, I hope . . . .
> 
> Hi Nicolas, thanks for your observations.  I'll try to answer your questions, 
> please see the attached map, especially Map A:
> 
> Note that my previous email contained information for Map B; Map A is based 
> on the Municipal Cadastre (NAD83 UTM zone 10N) and illustrates the problem as 
> well. Other locations based on Provincial Monuments and/or the Municipal 
> cadastre (not illustrated here) have yielded similar results.
> 
> How many “known” points have you tested?
> 2 in this case, Maps A and B
> Also several other locations with similar results
> How where those point position calculated.
> From the Municipal cadastre, visible in Map A
> Make sure the coordinates are in the right CRS
> NAD 83 UTM 10N used throught.  See workflow in previous email
> When converting from the monument’s CRS to NAD83 UTM zone 10N, are you using 
> the correct grid files?
> [No monuments in this example] These were brought into QGIS from the 
> Municipal GCM database CSV (NAD83(CSRS) 3.0.0.BC.1.CRD) and reprojected by 
> QGIS to EPSG:26910 - NAD83 / UTM zone 10N
> Presumably QGIS would choose the correct grid files
> Municipal Cadastre is NAD83 UTM zone 10N
> Find a geodesic point that is in the middle of a field or on the side of a 
> highway with no obstacles.
> Map A is open sky
> Make sur your observations will be done when the constellation is well 
> distributed in the sky
> As you probably know, TerraSync provides for PDOP, HDOP, SNR and Horizon 
> masks to preclude collecting poor quality positions. These were set towards 
> the "Precision" end of the scale
> What post processing techniques are you using? How far is the base station 
> from your unit?
> Real time was SBAS or RTCM; Post processing using the Pathfinder Office 
> differential correction engine, baseline about 30 km
> How long are the observations? Have you tried other methods of post 
> processing like PPP?
> Logging interval is 5 sec; 33 to 2037 positions per point
> Did not use PPP. This is a test of mapping best practices, not geodesy
> Have you contacted Trimble?
> Yes, no response
> Have you looked on there site to see if there is a software update (firmware) 
> for the unit or the post processing software?
> Yes, receiver firmware is the latest, PFO and Terrasync are older but 
> compatible
> Thanks Nicolas. If I have missed something, I hope someone can point it out, 
> I've tried to cover all the bases based on my training and experience.
> 
> -
> Cheers, Spring
> 
> 
> 
> On 08/Mar/2021 06:40, Nicolas Cadieux wrote:
>> Hi Harrison,
>> 
>> How many “known” points have you tested? How where those point position 
>> calculated. They could be off.  If you are using state geodesic monuments, 
>> try to find the documented precision of the monument. States have different 
>> types of monuments, some are very old and have different standards.  Make 
>> sure the geodesic point is not the problem.  Make sure the coordinates are 
>> in the right CRS.  As an example, if the coordinates are published in NAD83 
>> original but you are assuming NAD83(CSRS), then you have a problem. When 
>> converting from the monument’s CRS to NAD83 UTM zone 10N, are you using the 
>> correct grid files?  What is the published precision for this reprojection?
>> 
>> You say you have houses and trees.  This could be the problem.  Find a 
>> geodesic point that is in the middle of a field or on the side of a highway 
>> with no obstacles. Make sur your observations will be done when the 
>> constellation is well distributed in the sky.  I believe Trimble has a 
>> observation planing software that can help you fi

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

Hi SpringerI just looked up the marine beacon specs and they are designed for 
10m accuracy. This may explain why your non dgps data is closer to your survey 
corner.Sent from my Galaxy
 Original message From: Springfield Harrison 
 Date: 2021-03-08  3:17 p.m.  (GMT-04:00) To: Nicolas 
Cadieux  Cc: kirk , 
Jorge Gustavo Rocha , qgis-user@lists.osgeo.org, Greg Troxel 
, Dan <19dm...@gmail.com> Subject: Re: [Qgis-user] Trimble 
GeoXT 2005 Accuracy 
I'm resending this without the map as there is a size limit.  The moderator 
may let it through, I hope . . . .


Hi Nicolas, thanks for your observations.  I'll try to answer your 
questions, please see the attached map, especially Map A:
Note that my previous email contained information for Map B; Map A is based 
on the  Municipal Cadastre  (NAD83 UTM zone 10N) and illustrates the problem as 
well.  Other locations based on Provincial Monuments and/or the Municipal 
cadastre (not illustrated here) have yielded similar results.

  How many “known” points have you tested?
  
2 in this case, Maps A and B
Also several other locations with similar results

  
   How where those point position calculated.
  
From the Municipal cadastre, visible in Map A

  
  Make sure the coordinates are in the right CRS
  
NAD 83 UTM 10N used throught.  See workflow in previous email

  
   When converting from the monument’s CRS to NAD83 UTM zone 10N, are you 
using the correct grid files?
  
[No monuments in this example] These were brought into QGIS from the 
Municipal GCM database CSV (NAD83(CSRS) 3.0.0.BC.1.CRD) and reprojected by QGIS 
to EPSG:26910 - NAD83 / UTM zone 10N
Presumably QGIS would choose the correct grid files

Municipal Cadastre is  NAD83 UTM zone 10Np, li { white-space: pre-wrap; 
}
  
  Find a geodesic point that is in the middle of a field or on the side of 
a highway with no obstacles.
  
Map A is open sky

  
  Make sur your observations will be done when the constellation is well 
distributed in the sky
  
As you probably know, TerraSync provides for PDOP, HDOP, SNR and 
Horizon masks to preclude collecting poor quality positions.  These were set 
towards the "Precision" end of the scale

  
  What post processing techniques are you using? How far is the base 
station from your unit?
  
Real time was SBAS or RTCM; Post processing using the Pathfinder Office 
differential correction engine, baseline about 30 km

  
  How long are the observations? Have you tried other methods of post 
processing like PPP? 

  
Logging interval is 5 sec; 33 to 2037 positions per point
Did not use PPP.  This is a test of mapping best practices, not geodesy

  
  Have you contacted Trimble? 

  
Yes, no response

  
  Have you looked on there site to see if there is a software update 
(firmware) for the unit or the post processing software?
  
Yes, receiver firmware is the latest, PFO and Terrasync are older but 
compatible

  

Thanks Nicolas.  If I have missed something, I hope someone can point it 
out, I've tried to cover all the bases based on my training and experience.
-
Cheers, Spring






On 08/Mar/2021 06:40, Nicolas Cadieux
  wrote:


  
  Hi Harrison,
  
  
  How many “known” points have you tested? How where those
point position calculated. They could be off.  If you are using
state geodesic monuments, try to find the documented precision
of the monument. States have different types of monuments, some
are very old and have different standards.  Make sure the
geodesic point is not the problem.  Make sure the coordinates
are in the right CRS.  As an example, if the coordinates are
published in NAD83 original but you are assuming NAD83(CSRS),
then you have a problem. When converting from the monument’s CRS
to NAD83 UTM zone 10N, are you using the correct grid files?
 What is the published precision for this reprojection?
  
  
  You say you have houses and trees.  This could be the
problem.  Find a geodesic point that is in the middle of a field
or on the side of a highway with no obstacles. Make sur your
observations will be done when the constellation is well
distributed in the sky.  I believe Trimble has a observation
planing software that can help you figure out the best time for
observation. This could explain why the GEoTX are to the east
unless the  observations where made at the same time and same
conditions (ex leaf off).
  
  
  What post processing techniques are you using? How far is the
base station from your unit? If you a

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

Hi Springer.Thanks for providing the high level of detail.I assume the 
comparison of field units occurred at separate times or even days?In map 1, 
where were you standing in relation to the internal antenae. Your body will 
block and or distort radio signals.  It is good practice to set the field unit 
on a tripod or rock and move away from the unit while observing. Additionally, 
how did you set up the external antenae when you used it (tripod, pack pack?).I 
am not sure what the marine beacon accuracy is as we used them in eastern 
Canada during the days of selective availability.  WAAS may be totally useless 
in this application as the system is designed for coarse aircraft navigation to 
get down to 200' of a runway.Have a look at the Canadian Active Control system. 
Perhaps you are close to one if the federal or western deformation array  
sites. You can download the historical data for these sites which can include 
broadcast emphemerifes and clock corrections. I do not know if these sites are 
implemented in PFO. I assume you can import into PFO and DGPS. Kirk SchmidtSent 
from my Galaxy
 Original message From: Springfield Harrison 
 Date: 2021-03-08  3:17 p.m.  (GMT-04:00) To: Nicolas 
Cadieux  Cc: kirk , 
Jorge Gustavo Rocha , qgis-user@lists.osgeo.org, Greg Troxel 
, Dan <19dm...@gmail.com> Subject: Re: [Qgis-user] Trimble 
GeoXT 2005 Accuracy 
I'm resending this without the map as there is a size limit.  The moderator 
may let it through, I hope . . . .


Hi Nicolas, thanks for your observations.  I'll try to answer your 
questions, please see the attached map, especially Map A:
Note that my previous email contained information for Map B; Map A is based 
on the  Municipal Cadastre  (NAD83 UTM zone 10N) and illustrates the problem as 
well.  Other locations based on Provincial Monuments and/or the Municipal 
cadastre (not illustrated here) have yielded similar results.

  How many “known” points have you tested?
  
2 in this case, Maps A and B
Also several other locations with similar results

  
   How where those point position calculated.
  
From the Municipal cadastre, visible in Map A

  
  Make sure the coordinates are in the right CRS
  
NAD 83 UTM 10N used throught.  See workflow in previous email

  
   When converting from the monument’s CRS to NAD83 UTM zone 10N, are you 
using the correct grid files?
  
[No monuments in this example] These were brought into QGIS from the 
Municipal GCM database CSV (NAD83(CSRS) 3.0.0.BC.1.CRD) and reprojected by QGIS 
to EPSG:26910 - NAD83 / UTM zone 10N
Presumably QGIS would choose the correct grid files

Municipal Cadastre is  NAD83 UTM zone 10Np, li { white-space: pre-wrap; 
}
  
  Find a geodesic point that is in the middle of a field or on the side of 
a highway with no obstacles.
  
Map A is open sky

  
  Make sur your observations will be done when the constellation is well 
distributed in the sky
  
As you probably know, TerraSync provides for PDOP, HDOP, SNR and 
Horizon masks to preclude collecting poor quality positions.  These were set 
towards the "Precision" end of the scale

  
  What post processing techniques are you using? How far is the base 
station from your unit?
  
Real time was SBAS or RTCM; Post processing using the Pathfinder Office 
differential correction engine, baseline about 30 km

  
  How long are the observations? Have you tried other methods of post 
processing like PPP? 

  
Logging interval is 5 sec; 33 to 2037 positions per point
Did not use PPP.  This is a test of mapping best practices, not geodesy

  
  Have you contacted Trimble? 

  
Yes, no response

  
  Have you looked on there site to see if there is a software update 
(firmware) for the unit or the post processing software?
  
Yes, receiver firmware is the latest, PFO and Terrasync are older but 
compatible

  

Thanks Nicolas.  If I have missed something, I hope someone can point it 
out, I've tried to cover all the bases based on my training and experience.
-
Cheers, Spring






On 08/Mar/2021 06:40, Nicolas Cadieux
  wrote:


  
  Hi Harrison,
  
  
  How many “known” points have you tested? How where those
point position calculated. They could be off.  If you are using
state geodesic monuments, try to find the documented precision
of the monument. States have different types of monuments, some
are very old and have different standards.  Make sure the
geodesic point is not the problem.  Make sure the coordinates
are in the right CRS.  As an example, if the coordinates are
published in NAD83 original but you are assuming NAD83(CSRS),
 

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

 a tablet based tree inventory using SW Maps with a Total 
Station survey as many of the trees are near the property boundary.  
Some of the tablet errors are quite large. Due to the tree canopy, 
GPS quality is variable.


I know that many people use tablets and hiking GPS as mapping tools 
but I have little faith in them for that purpose.


For many years my work flow has been: Trimble Receiver + RTCM/SBAS -> 
Pathfinder Office [+ RINEX Post Processing] -> SHP files -> GIS (QGIS 
or Manifold GIS).  The CRS is NAD83 UTM 10N throughout, for my home 
area at least.


None of these steps offer any option to choose or modify the Base 
Station CRS so I don't think that would be the culprit in my NW data 
offset, although maybe I've missed something.


Last fall I collected quite a few points in an attempt to quantify 
the problem, if that's what it is.  Here are some summaries:


*Average distance from "Known" point (m)*

Location

*Receiver*  *Correction**Corner**IP NW* *Grand Total*
GeoXT   Post1.441.44
SBAS1.371.261.33
Uncorr  0.73
0.73
GeoXT Total *1.34*  *1.26*  *1.32*
ProXR   RTCM0.380.610.49
ProXR Total *0.38*  *0.61*  *0.49*
Grand Total *1.17*  *0.97*  *1.12*



LocationData



*Count of Feature Points and Positions*

Corner  IP NW   Total Count of Point_ID Total 
Sum of Filt_Pos
*Receiver* 	*Correction* 	*Count of Point_ID* 	*Filt_Pos* 	*Count of 
Point_ID* 	*Filt_Pos* 	** 	**

GeoXT   Post9   14929   1492
SBAS8   12805   905 13  2185
Uncorr  2   2836
2   2836
GeoXT Total *19**5608*  *5* *905*   *24**6513*
ProXR   RTCM4   25414   683 8   3224
ProXR Total *4* *2541*  *4* *683*   *8* *3224*
Grand Total *23**8149*  *9* *1588*  *32**9737*

Corrected test Points and separation from the antenna location.



As above but with 2 uncorrected GeoXT points overlaid, including the 
individual positions that were averaged.




Notes and findings:

 1. Site is open sky but with house and trees adjacent
 2. Antenna is static, occupation periods long (5 sec logging interval)
 3. 32 observations averaged from 9737 positions
 4. some observations are with the GeoXT internal antenna, others are
with a Trimble aircraft antenna (intended for SBAS)
 5. Work flow as outlined above
 6. The GeoXT uncorrected results are better than either of the
corrected results!?
 7. The corrected ProXR results are better than any of the GeoXT
results, although biased to the east
 8. The uncorrected GeoXT readings exhibit the NW bias but to a
lesser extent which seems to indicate that the correction does
not create the problem but may exacerbate it, if that makes any
sense.
 9. I have probably missed something but my reaction remains that the
receiver may be defective (?)

Thanks again for your help and patience . . . . .

-
Cheers, Spring


On 07/Mar/2021 03:54, kirk wrote:

Hi Springer.

I assume your raw data files are being converted to gpx on  a 
computer since the raw terrasync files are proprietary binary files. 
If you are using trimble pathfinder, you can post process 
differentialy correct the data if you have access to  base station 
logged at the same time you captured your field data. Having a base 
station 100 miles away will not improve your results as the baseline 
is too long.


I do not know if you can write a gpx file directly from pathfinder 
but I would not bother. I would write a shapefile which will contain 
the coordinate system you specify.  Simply open in qgis and you 
should be good to go. If your older unit works better, I would 
expect it may be an issue with the setup within pathfinder or 
perhaps the software version.


I think your consistent offset is a direct result of how you are 
converting your data from trimble to gpx.


As I mentioned in my previous comments, there are many issues which 
affect accuracy.  Just because the box says it is accurate  you will 
rarely replicate that in the field.


In terms of WAAS dataframes, these are processed internally on your 
field unit.


Kirk Schmidt



Sent from my Galaxy


 Original message 
From: Springfield Harrison 
Date: 2021-03-07 5:57 a.m. (GMT-04:00)
To: kirk , Jorge Gustavo Rocha 
, qgis-user@lists.osgeo.org, Greg Troxel 
, Dan <19dm...@gmail.com>, Nicolas Cadieux 


Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

Hello All, Thanks for the comments, I'll reply more fully tomorrow. 
The receiver is Trimble mapping grade: "The GeoExplorer 2005 series 
consists of: • The GeoXH™ handheld, providing subfoot (30 cm) 
accuracy, or eve

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hi Greg,

The cadastre is a provincial entity:

https://www2.gov.bc.ca/gov/content/data/geographic-data-services/land-use/integrated-cadastral-fabric

A quick search didn't reveal accuracy specs but because these are legal 
entities they have to be tight.  Just talked to someone who manged this 
for our municipality.  He says 10 cm, 30 at the worst and the orthophoot 
tie in to the cadastre also very good, at least at ground level.


"Or does your jurisdiction have a requirement for coordinates good to
<10cm to be submitted on transfer, and there really is a survey tied to
CSRS?"

This does seem to be the case here. How is it done in Massachusetts?

I've checked several other points, see previous posts.

Thanks Greg . . . . .

-
Cheers, Spring



On 08/Mar/2021 10:10, Greg Troxel wrote:

I don't konw why you believe the cadastre to be sub-meter:
   What is the published accuracy spec?
   How many other points have you checked?

Perhaps you can answer those on-thread.



Or does your jurisdiction have a requirement for coordinates good to
<10cm to be submitted on transfer, and there really is a survey tied to
CSRS?  This would very surprising to me, but Massachusetts doesn't work
that way at all.

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hi Greg,

Comments inserted below -

-
Cheers, Spring


On 08/Mar/2021 08:36, Greg Troxel wrote:

[I'm not sure how on-topic this is for qgis-user, but I'm guessing it's
relevant enough, at least until a Moderator comment otherwise.]
You're right but I took my que from other GPS related threads and lack 
of response from Trimble.

Springfield Harrison  writes:

To figure out what's going on this description needs to be tightened up,
which is probably going to require trimble documentation or support to
clearer (maybe the docs are fine; I haven't looked).

I'm familiar with the docs and no help from Trimble.

For many years my work flow has been:
Trimble Receiver + RTCM/SBAS ->

This is unusual phrasing.  SBAS is a class of things, not a particular
corrections source.  I'm guessing you are in North America and this
really means WAAS.

RTCM is a family of protocols for transporting corrections.  I am
unclear on whether the WAAS format uses RTCM but I don't remember seeing
it.  Within RTCM there is RTCM2, usually used for pseuorange
corrections, and RTCM3, usually used for carrier phase reference data.

So I wonder if the ProXR is doing RTK, what the correction source is,
and what the distance to the base station is (or if it's VRS).

To me the most important thing to be precise about is pseudorange
solutions (often called navigation solutions) vs carrier phase solutions
(post processed or RTK).  Then, there's PPP which is harder to
understand.

So I think you mean that while you were collecting points the receiver
was calculating pseudorange solutions and using the pseudorange
corrections delivered by WAAS.


Yes!  I use SBAS because Trimble does in TerrasSync but it does mean 
WAAS in southern BC, I think.  They don't use WAAS because the SBAS may 
use a different correction source elsewhere in the world.  I enable 
carrier measurements in TerraSync most of the time.


Again, following Trimble terminology, RTCM in this case is a marine 
beacon.  I have no source for RTK.



Pathfinder Office [+ RINEX Post Processing] -> SHP files -> GIS (QGIS
or Manifold GIS).

You say "RINEX Post Processing" but that leaves out a ton of important
details.   I am guessing you mean that the receiver records carrier
phase observables, and then there was a double-differenced carrier phase
solution for each ooccupation.   The obvious question is where the
reference station data is coming from, how far away it is (or is it some
VRS), and what datum the reference station coordiantes are in.

Or maybe this is doing PPP.  There, similar questions apply about where
the orbit data is coming from and what frame that is in.
I use the Pathfinder Office Post Processing engine which looks after the 
technical details.  I select a base station from their provided list, 
sorted by distance and it fetches the (RINEX?) files and applies the 
corrections.  I think the distance was about 30km.  PFO makes no 
provision for specifying or modifying the base station CRS.  It is 
encoded in the RINEX files.  It will utilize carrier phase data if it 
available in the rover file.

  The CRS is NAD83 UTM 10N throughout, for my home area at least.

There are many realizations of NAD83.  Anything you did last year is
likely in "NAD83(2011) epoch 2010.0" if you are in the US and firmly on
the North American plate, and in Canada likely in NAD83(CSRS) apparently
in a province-dependent epoch.  The recent realizations are close enough
that neglecting this won't hurt too much, but if you are going to call
1m an error rather than a match, you should be careful about this.
My concern is not the absolute error but the systematic shift of all the 
points to the NW; the precision seems quite good, it is the accuracy 
that I question.  I think the different flavours of NAD83 UTM zone 10N 
differ by centimeters at most (?)

If you are in an area with ground motion (e.g. Pacific Plate) then you
have a lot more to do.

I am but how is this relevant, this is mm per year?

The other big thing that's missing is what the trimble software is doing
about datum transformations (or not, if the reference station
coordinates are in NAD83(2011) as I'd expect).
Datum transformations where?  Their post processing process is "under 
the hood", QGIS datum transformations are much the same.  I have some 
faith (but not total) that they are being handled correctly.  This is 
supposed to be mapping, not geodesy.

 None of these steps offer any option to choose or modify the Base
   Station CRS so I don't think that would be the culprit in my NW
   data offset, although maybe I've missed something.

I think it's necessary to understand what's going on inside the software.
Maybe, but that would be Trimble proprietary stuff, presumably. Their 
intent is to provide a streamlined workflow that incorporates all the 
myriad technical gymnastics but only exposes me to the NECESSARY 
details.  I'm sure that research grade differential software would 
reveal most of the 

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Greg Troxel]

[I'm not sure how on-topic this is for qgis-user, but I'm guessing it's
relevant enough, at least until a Moderator comment otherwise.]

Springfield Harrison  writes:

To figure out what's going on this description needs to be tightened up,
which is probably going to require trimble documentation or support to
clearer (maybe the docs are fine; I haven't looked).

> For many years my work flow has been:
> Trimble Receiver + RTCM/SBAS ->

This is unusual phrasing.  SBAS is a class of things, not a particular
corrections source.  I'm guessing you are in North America and this
really means WAAS.

RTCM is a family of protocols for transporting corrections.  I am
unclear on whether the WAAS format uses RTCM but I don't remember seeing
it.  Within RTCM there is RTCM2, usually used for pseuorange
corrections, and RTCM3, usually used for carrier phase reference data.

So I wonder if the ProXR is doing RTK, what the correction source is,
and what the distance to the base station is (or if it's VRS).

To me the most important thing to be precise about is pseudorange
solutions (often called navigation solutions) vs carrier phase solutions
(post processed or RTK).  Then, there's PPP which is harder to
understand.

So I think you mean that while you were collecting points the receiver
was calculating pseudorange solutions and using the pseudorange
corrections delivered by WAAS.

> Pathfinder Office [+ RINEX Post Processing] -> SHP files -> GIS (QGIS
> or Manifold GIS).

You say "RINEX Post Processing" but that leaves out a ton of important
details.   I am guessing you mean that the receiver records carrier
phase observables, and then there was a double-differenced carrier phase
solution for each ooccupation.   The obvious question is where the
reference station data is coming from, how far away it is (or is it some
VRS), and what datum the reference station coordiantes are in.

Or maybe this is doing PPP.  There, similar questions apply about where
the orbit data is coming from and what frame that is in.

>  The CRS is NAD83 UTM 10N throughout, for my home area at least.

There are many realizations of NAD83.  Anything you did last year is
likely in "NAD83(2011) epoch 2010.0" if you are in the US and firmly on
the North American plate, and in Canada likely in NAD83(CSRS) apparently
in a province-dependent epoch.  The recent realizations are close enough
that neglecting this won't hurt too much, but if you are going to call
1m an error rather than a match, you should be careful about this.

If you are in an area with ground motion (e.g. Pacific Plate) then you
have a lot more to do.

The other big thing that's missing is what the trimble software is doing
about datum transformations (or not, if the reference station
coordinates are in NAD83(2011) as I'd expect).


> None of these steps offer any option to choose or modify the Base
>   Station CRS so I don't think that would be the culprit in my NW
>   data offset, although maybe I've missed something.

I think it's necessary to understand what's going on inside the software.

> Last fall I collected quite a few points in an attempt to
>   quantify the problem, if that's what it is.  Here are some
>   summaries:

As Nicolas said, you are talking about "known" but have not explained
where those coordinates came from and their expected errors.   I also
can't figure out your color scheme, and whether you are measuring 2
marks or one, etc.

Data from the receiver in no-differential pseudorange solutio mode (not
sure what "uncorrected" means) is going to be in WGS84(G1762), probably
labeled as WGS84, which is different than NAD83(2011), and that needs a
datum transform.  In QGIS, that often ends up with a null transform,
which is wrong.  So there's a good question about what is going on
within Pathfinder Office with datum transforms, which you need to find
out from Trimble docs or support.


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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Nicolas Cadieux]

 averaged from 9737 positions
> some observations are with the GeoXT internal antenna, others are with a 
> Trimble aircraft antenna (intended for SBAS)
> Work flow as outlined above
> The GeoXT uncorrected results are better than either of the corrected 
> results!?
> The corrected ProXR results are better than any of the GeoXT results, 
> although biased to the east
> The uncorrected GeoXT readings exhibit the NW bias but to a lesser extent 
> which seems to indicate that the correction does not create the problem but 
> may exacerbate it, if that makes any sense.
> I have probably missed something but my reaction remains that the receiver 
> may be defective (?)
> Thanks again for your help and patience . . . . .
> 
> -
> Cheers, Spring
> 
> 
>> On 07/Mar/2021 03:54, kirk wrote:
>> Hi Springer.
>> 
>> I assume your raw data files are being converted to gpx on  a computer since 
>> the raw terrasync files are proprietary binary files. If you are using 
>> trimble pathfinder, you can post process differentialy correct the data if 
>> you have access to  base station logged at the same time you captured your 
>> field data.  Having a base station 100 miles away will not improve your 
>> results as the baseline is too long.
>> 
>> I do not know if you can write a gpx file directly from pathfinder but I 
>> would not bother. I would write a shapefile which will contain the 
>> coordinate system you specify.  Simply open in qgis and you should be good 
>> to go. If your older unit works better, I would expect it may be an issue 
>> with the setup within pathfinder or perhaps the software version.
>> 
>> I think your consistent offset is a direct result of how you are converting 
>> your data from trimble to gpx.
>> 
>> As I mentioned in my previous comments, there are many issues which affect 
>> accuracy.  Just because the box says it is accurate  you will rarely 
>> replicate that in the field.  
>> 
>> In terms of WAAS dataframes, these are processed internally on your field 
>> unit.
>> 
>> Kirk Schmidt 
>> 
>> 
>> 
>> Sent from my Galaxy
>> 
>> 
>>  Original message 
>> From: Springfield Harrison 
>> Date: 2021-03-07 5:57 a.m. (GMT-04:00)
>> To: kirk , Jorge Gustavo Rocha 
>> , qgis-user@lists.osgeo.org, Greg Troxel 
>> , Dan <19dm...@gmail.com>, Nicolas Cadieux 
>> 
>> Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy
>> 
>> Hello All,
>> 
>> Thanks for the comments, I'll reply more fully tomorrow.
>> 
>> The receiver is Trimble mapping grade:
>> 
>> "The GeoExplorer 2005 series consists of:
>> • The GeoXH™ handheld, providing subfoot (30 cm) accuracy, or even 8-inch 
>> (20 cm) accuracy
>> with the optional Zephyr™ antenna.
>> • The GeoXT™ handheld offering submeter accuracy for GIS data collection and 
>> data
>> maintenance.
>> • The GeoXM™ handheld with 1–3 meter GPS accuracy for mobile GIS 
>> applications."
>> 
>> "Post processed carrier accuracy: 1-30cm".  This receiver was probably 
>> $5-8000 (?) new.
>> 
>> Data collection was stationary, open sky, good satellite coverage, several 
>> minutes of 5 sec observations, good PDOP
>> SBAS and/or post processed
>> The concern is not the accuracy as such, but the systematic NW shift.  This 
>> has been observed over several months, consistently.  My old Trimble ProXR 
>> (1994?, $20K new!) is actually better in this regard than the GeoXT!
>> 
>> The Trimble manuals make no mention of the SBAS CRS, implying "turn it on 
>> and go, the receiver will integrate the SBAS into the rover file."  
>> 
>> More tomorrow, thanks . . . . .
>> 
>> -
>> Cheers, Spring
>> 
>> 
>> 
>>> On 06/Mar/2021 15:56, kirk wrote:
>>> A few notes.
>>> 
>>> sbas which is waas in north America is based on equatorial satellites which 
>>> will get you in the 1 m range in southern Canada. 
>>> 
>>> you can achieve sub decimeter accuracy consistently using rtk ,either 
>>> through a ntrip  caster (base station) broadcasting over the intenet or 
>>> with your own base station and a radio link. there are a few chip sets and 
>>> break out boards that you acquire and assemble your own system. This is a 
>>> very inexpensive option.
>>> 
>>> Another option in Canada is to use precise point positioning (PPP) which 
>>> requires 6 to 12 hours of observation data using L1, L2 or L1 and L2

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

Hi Springer.I assume your raw data files are being converted to gpx on  a 
computer since the raw terrasync files are proprietary binary files. If you are 
using trimble pathfinder, you can post process differentialy correct the data 
if you have access to  base station logged at the same time you captured your 
field data.  Having a base station 100 miles away will not improve your results 
as the baseline is too long.I do not know if you can write a gpx file directly 
from pathfinder but I would not bother. I would write a shapefile which will 
contain the coordinate system you specify.  Simply open in qgis and you should 
be good to go. If your older unit works better, I would expect it may be an 
issue with the setup within pathfinder or perhaps the software version.I think 
your consistent offset is a direct result of how you are converting your data 
from trimble to gpx.As I mentioned in my previous comments, there are many 
issues which affect accuracy.  Just because the box says it is accurate  you 
will rarely replicate that in the field.  In terms of WAAS dataframes, these 
are processed internally on your field unit.Kirk Schmidt Sent from my Galaxy
 Original message From: Springfield Harrison 
 Date: 2021-03-07  5:57 a.m.  (GMT-04:00) To: kirk 
, Jorge Gustavo Rocha , 
qgis-user@lists.osgeo.org, Greg Troxel , Dan 
<19dm...@gmail.com>, Nicolas Cadieux  Subject: Re: 
[Qgis-user] Trimble GeoXT 2005 Accuracy 
Hello All,
  
  Thanks for the comments, I'll reply more fully tomorrow.
  
  The receiver is Trimble mapping grade:
  
  "The GeoExplorer 2005 series consists of:
  • The GeoXH™ handheld, providing subfoot (30 cm) accuracy, or even
  8-inch (20 cm) accuracy
  with the optional Zephyr™ antenna.
  • The GeoXT™ handheld offering submeter accuracy for GIS data
  collection and data
  maintenance.
  • The GeoXM™ handheld with 1–3 meter GPS accuracy for mobile GIS
  applications."
  
  "Post processed carrier accuracy: 1-30cm".  This receiver was
  probably $5-8000 (?) new.


  Data collection was stationary, open sky, good satellite
coverage, several minutes of 5 sec observations, good PDOP
  SBAS and/or post processed
  

The concern is not the accuracy as such, but the systematic NW
  shift.  This has been observed over several months, consistently. 
  My old Trimble ProXR (1994?, $20K new!) is actually better in this
  regard than the GeoXT!
  
  The Trimble manuals make no mention of the SBAS CRS, implying
  "turn it on and go, the receiver will integrate the SBAS into the
  rover file."  
  
  More tomorrow, thanks . . . . .

-
Cheers, Spring






On 06/Mar/2021 15:56, kirk wrote:


  
  A few notes.
  
  
  sbas which is waas in north America is based on
equatorial satellites which will get you in the 1 m range in
southern Canada. 
  
  
  you can achieve sub decimeter accuracy
consistently using rtk ,either through a ntrip  caster (base
station) broadcasting over the intenet or with your own base
station and a radio link. there are a few chip sets and break
out boards that you acquire and assemble your own system. This
is a very inexpensive option.
  
  
  Another option in Canada is to use precise point
positioning (PPP) which requires 6 to 12 hours of observation
data using L1, L2 or L1 and L2 data and rinex log files. This
comes in handy if you need to establish a remote base station.
  
  
  A proper antennae with a metal ground plane is
also critical to getting quality results.
  
  
  Observing under a forested canopy is difficult
especially in summer under leaf on conditions,  after a rain
which creates multiparth mayhem.
  
  
  There is a reason survey grade equipment is
relatively expensive. If you require repeatably accurate results
in a variety of conditions this is an option.
  
  
  Kirk Schmidt 
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
Sent from my
  Galaxy
  
  
  
  
  
  
 Original message 
From: Jorge Gustavo Rocha  
Date: 2021-03-06 6:41 p.m. (GMT-04:00) 
To: qgis-user@lists.osgeo.org 
    Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy 


  
  Hi,
  I just jump in this thread to say I'm really impressed with
Ardusimple. I have a RTK Handheld Surveyor Kit [1] for +- 400 €
and it works really well.
  I use the national NTRIP service and I have consistently
precisions around 10 cm with just one receiver

Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hello All,

Thanks for the comments, I'll reply more fully tomorrow.

The receiver is Trimble mapping grade:

"The GeoExplorer 2005 series consists of:
• The GeoXH™ handheld, providing subfoot (30 cm) accuracy, or even 
8-inch (20 cm) accuracy

with the optional Zephyr™ antenna.
• The GeoXT™ handheld offering submeter accuracy for GIS data collection 
and data

maintenance.
• The GeoXM™ handheld with 1–3 meter GPS accuracy for mobile GIS 
applications."


"Post processed carrier accuracy: 1-30cm".  This receiver was probably 
$5-8000 (?) new.


 * Data collection was stationary, open sky, good satellite coverage,
   several minutes of 5 sec observations, good PDOP
 * SBAS and/or post processed

The concern is not the accuracy as such, but the systematic NW shift.  
This has been observed over several months, consistently. My old Trimble 
ProXR (1994?, $20K new!) is actually better in this regard than the GeoXT!


The Trimble manuals make no mention of the SBAS CRS, implying "turn it 
on and go, the receiver will integrate the SBAS into the rover file."


More tomorrow, thanks . . . . .

-
Cheers, Spring




On 06/Mar/2021 15:56, kirk wrote:

A few notes.

sbas which is waas in north America is based on equatorial satellites 
which will get you in the 1 m range in southern Canada.


you can achieve sub decimeter accuracy consistently using rtk ,either 
through a ntrip  caster (base station) broadcasting over the intenet 
or with your own base station and a radio link. there are a few chip 
sets and break out boards that you acquire and assemble your own 
system. This is a very inexpensive option.


Another option in Canada is to use precise point positioning (PPP) 
which requires 6 to 12 hours of observation data using L1, L2 or L1 
and L2 data and rinex log files. This comes in handy if you need to 
establish a remote base station.


A proper antennae with a metal ground plane is also critical to 
getting quality results.


Observing under a forested canopy is difficult especially in summer 
under leaf on conditions,  after a rain which creates multiparth mayhem.


There is a reason survey grade equipment is relatively expensive. If 
you require repeatably accurate results in a variety of conditions 
this is an option.


Kirk Schmidt







Sent from my Galaxy


 Original message 
From: Jorge Gustavo Rocha 
Date: 2021-03-06 6:41 p.m. (GMT-04:00)
To: qgis-user@lists.osgeo.org
Subject: Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

Hi,

I just jump in this thread to say I'm really impressed with 
Ardusimple. I have a RTK Handheld Surveyor Kit [1] for +- 400 € and it 
works really well.


I use the national NTRIP service and I have consistently precisions 
around 10 cm with just one receiver.


I use a free Android application called SW Maps [2]. My survey points, 
tracks and photos are collect in a geopackage that I can read in QGIS. 
I use it mostly to collect ground control points for my drone flights.


Regards,

Jorge Gustavo

[1] https://www.ardusimple.com/product/rtk-handheld-surveyor-kit/

[2] https://play.google.com/store/apps/details?id=np.com.softwel.swmaps

Às 20:12 de 06/03/21, Greg Troxel escreveu:

Springfield Harrison  writes:


Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds
interesting, will have a look.

I have an earlier Emlid Reach (not RS or RS2), which has L1 only, and I
never got it to work well.

Also look at the Ardusimple unit -- but it's more a parts kit than a
system.  You need a way to get RTK reference data in, and a good
antenna.  One approach is Vespucci (OSM editor for Android) as a
datalogger, and the Ardusimple WiFi NTRIP master to get corrections over
the phone's hotspot.

   https://www.ardusimple.com/product/simplertk2b/

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Nicolas Cadieux]

Yes the Emlid unit is quite interesting for the price...

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 6 mars 2021 à 11:04, Dan <19dm...@gmail.com> a écrit :
> 
> 
> Kirk is spot on. That unit is for GIS use and cannot receive RTK GNSS 
> corrections. You will need a survey grade receiver, with RTK corrections (or 
> post processed) for better accuracy.
> 
> Budget option for cm accuracy is the Emlid Reach RS or RS2
> 
>> On Sat, 6 Mar 2021 at 23:53, Greg Troxel  wrote:
>> 
>> Springfield Harrison  writes:
>> 
>> > I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the
>> > results it produces:
>> >
>> > 1. Compared to a variety of "known" points, it consistently records
>> >positions that appear to be in error by 1.2 - 1.5 m NW from the
>> >known point.
>> > 2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
>> > 3. The known points include property survey pins, Government control
>> >survey monuments, Total Station survey points derived from the
>> >above, other GPS results (Trimble ProXRS) and identifiable points on
>> >orthophotos.
>> > 4. I'm using SBAS correction in the GeoXT.
>> >
>> > It appears to be adding a consistent offset to the GPS result although
>> > no offset has been set in TerraSync.
>> >
>> > Many thanks for any thoughts on this situation . . . . .
>> 
>> I'm really not clear on what this particular receiver is purporting to
>> do, but a consistent meter-ish offset smells like an incorrect datum.
>> 
>> If you are using SBAS and in the US, that means WAAS.  So you are
>> getting results that in some CRS that the list hasn't figured out what
>> it is, but "ITRF2008 current epoch" is my best guess.  That's
>> essentially equal to "WGS84(G1762) current epoch".
>> 
>> Those frames are definitely not equal to any flavor of NAD83.
>> 
>> qgis, via proj, will treat "WGS84"  and "NAD83" both as datum ensembles
>> and because each ensemble has a low-accuracy member treat them as equal,
>> and thus choose a null transform.  IMHO this is the wrong thing to do,
>> as WGS84(G1762) and NAD83(2011) are both datums with high intrinsic
>> accuracy and are definitely not  equivalent.
>> 
>> Converting from ITRF2014 to NAD83(2011) will apply a datum shift.
>> 
>> Advice 1 is to shift your project CRS from NAD83 to ITRF2014 and see if
>> the relative position of the observations and controls changes.   If so,
>> you have datum transform trouble.
>> 
>> My real advice 2 is to take the data file from the unit and label it as
>> ITRF2014, and then see how things line up.  If you are talking about a
>> meter you need to really pay very close attention not only to datum
>> labeling but also in understanding the transformations your software is
>> making.
>> 
>> Greg
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

A few notes.sbas which is waas in north America is based on equatorial 
satellites which will get you in the 1 m range in southern Canada. you can 
achieve sub decimeter accuracy consistently using rtk ,either through a ntrip  
caster (base station) broadcasting over the intenet or with your own base 
station and a radio link. there are a few chip sets and break out boards that 
you acquire and assemble your own system. This is a very inexpensive 
option.Another option in Canada is to use precise point positioning (PPP) which 
requires 6 to 12 hours of observation data using L1, L2 or L1 and L2 data and 
rinex log files. This comes in handy if you need to establish a remote base 
station.A proper antennae with a metal ground plane is also critical to getting 
quality results.Observing under a forested canopy is difficult especially in 
summer under leaf on conditions,  after a rain which creates multiparth 
mayhem.There is a reason survey grade equipment is relatively expensive. If you 
require repeatably accurate results in a variety of conditions this is an 
option.Kirk Schmidt Sent from my Galaxy
 Original message From: Jorge Gustavo Rocha  
Date: 2021-03-06  6:41 p.m.  (GMT-04:00) To: qgis-user@lists.osgeo.org Subject: 
Re: [Qgis-user] Trimble GeoXT 2005 Accuracy 
Hi,
I just jump in this thread to say I'm really impressed with
  Ardusimple. I have a RTK Handheld Surveyor Kit [1] for +- 400 €
  and it works really well.
I use the national NTRIP service and I have consistently
  precisions around 10 cm with just one receiver. 

I use a free Android application called SW Maps [2]. My survey
  points, tracks and photos are collect in a geopackage that I can
  read in QGIS. I use it mostly to collect ground control points for
  my drone flights.

Regards,
Jorge Gustavo

[1] https://www.ardusimple.com/product/rtk-handheld-surveyor-kit/
[2]
  https://play.google.com/store/apps/details?id=np.com.softwel.swmaps
Às 20:12 de 06/03/21, Greg Troxel
  escreveu:


  Springfield Harrison  writes:


  
Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds
interesting, will have a look.

  
  I have an earlier Emlid Reach (not RS or RS2), which has L1 only, and I
never got it to work well.

Also look at the Ardusimple unit -- but it's more a parts kit than a
system.  You need a way to get RTK reference data in, and a good
antenna.  One approach is Vespucci (OSM editor for Android) as a
datalogger, and the Ardusimple WiFi NTRIP master to get corrections over
the phone's hotspot.

  https://www.ardusimple.com/product/simplertk2b/

  
  
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Nicolas Cadieux]

Hi,
I don’t currently have enough internet to check out the unit but I imagine this 
is a single band unit with an onboard antenna.  I imagine you are using it in 
“point and shoot mode” or static mode where you are not taking measurements 
over a long period  time, nor are you using a second unit for correction or 
doing any kind of post processing.  If this is the case, you are getting a very 
good reading!

Getting a systematic error in the same area (NW) would indicate you are getting 
a bad satellite coverage or that perhaps, you have a obstacles.

Make sure you have a clear sky, that the unit has been working for 10 to 20 
minutes before the reading, that the satellites are well distributed and that 
you are picking up up 4 or more (8 or more is better).  Take multiple reading 
on the same point over a long period (you can average out the positions) make 
sure you don’t have another unit close by.  Using satellite from other 
constellation (like the Russian gps) can make thing more problematic some 
times.  

This is good for static mode where you just point and shoot and get a instant 
reading.  Anything under 5 m with a 200$ to 1000$ unit is good.  Anything under 
1m with a 1500$ to 4000$ unit is good.

Nicolas Cadieux
https://gitlab.com/njacadieux

> Le 6 mars 2021 à 03:35, Springfield Harrison  a écrit :
> 
> 
> Hello All,
> 
> I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the results 
> it produces:
> 
> Compared to a variety of "known" points, it consistently records positions 
> that appear to be in error by 1.2 - 1.5 m NW from the known point.  
> Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.  
> The known points include property survey pins, Government control survey 
> monuments, Total Station survey points derived from the above, other GPS 
> results (Trimble ProXRS) and identifiable points on orthophotos.  
> I'm using SBAS correction in the GeoXT.
> It appears to be adding a consistent offset to the GPS result although no 
> offset has been set in TerraSync.
> 
> Many thanks for any thoughts on this situation . . . . .
> 
> -
> Cheers, Springfield Harrison
> 
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Jorge Gustavo Rocha]

Hi,

I just jump in this thread to say I'm really impressed with Ardusimple.
I have a RTK Handheld Surveyor Kit [1] for +- 400 € and it works really
well.

I use the national NTRIP service and I have consistently precisions
around 10 cm with just one receiver.

I use a free Android application called SW Maps [2]. My survey points,
tracks and photos are collect in a geopackage that I can read in QGIS. I
use it mostly to collect ground control points for my drone flights.

Regards,

Jorge Gustavo

[1] https://www.ardusimple.com/product/rtk-handheld-surveyor-kit/

[2] https://play.google.com/store/apps/details?id=np.com.softwel.swmaps

Às 20:12 de 06/03/21, Greg Troxel escreveu:
> Springfield Harrison  writes:
>
>> Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds
>> interesting, will have a look.
> I have an earlier Emlid Reach (not RS or RS2), which has L1 only, and I
> never got it to work well.
>
> Also look at the Ardusimple unit -- but it's more a parts kit than a
> system.  You need a way to get RTK reference data in, and a good
> antenna.  One approach is Vespucci (OSM editor for Android) as a
> datalogger, and the Ardusimple WiFi NTRIP master to get corrections over
> the phone's hotspot.
>
>   https://www.ardusimple.com/product/simplertk2b/
>
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Greg Troxel]

Springfield Harrison  writes:

> My assumption (now it seems likely wrong) was that SBAS (WAAS in
> southern BC?) would "adapt" to the CRS designated in the receiver
> (NAD83, UTN 10N) and was also localized to the field location (as in
> Wide Area).  Thus QGIS would see the resulting NAD83, UTM 10N SHP file
> as compatible with the project CRS in QGIS (EPSG:26910, NAD83 UTM
> 10N).

You might be right and this is certainly complicated.

GPS navigation solutions without differential are in WGS84(G1762)
because that's the frame the orbits are expressed in.   When you are in
SBAS mode, control stations receive signals and compare pseudoranges to
the expected ones *given the known ITRF2008 coordinates of the reference
stations*, and then encode deltas so that a receiver can calculate the
error to back out as a function of the current time and the current
position.   After doing that, the receiver's solution is in ITRF2008,
not WGS84(G1762), but they are effectively the same thing.

In Garmin navigation-type receivers, data is logged in the solution
frame (labeled as WGS84) regardless of the display.

I really wonder what bits are recorded when you do this, what bits are
transferred, and then what transformation happens before you get a shapefile.

> I'm not sure why I would need to know or use the SBAS Reference Frame
> although the receiver certainly would.

It really depends on what happens in the receiver.

If you were using a local differential reference that was in
NAD83(2011), then the navigation solution would be in NAD83 but the
receiver might not know that.   This is what happens with RTK.

> Changing the project CRS to ITRF2014 (there are 3!, WTF, I used 7912)
> didn't change anything.

One of them is 2D, and one is XYZ.  7912 is the right call.

> I've since deferentially corrected the data with mixed results, some
> better, some worse, relatively.  I need to look at that further.

?

> Anyway, if Pathfinder Office produces a NAD83 UTM 10N SHP file from my
> SSF file (NAD83 UTM 10N), should that not project happily in QGIS set
> to EPSG:26910?  I think the datum transformations would take place in
> the receiver (in concert with SBAS) and Pathfinder Office.

Yes, if the data is properly transformed to NAD83(2011) before QGIS gets
it and QGIS is using some NAD83(2011) all should be ok.

> Perhaps there is more to this, I certainly appreciate your thoughts . . . .

You said consistently 1.2m ish.   I would go measure the same point
maybe 5 times on different days and look at the spread.


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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

OK, thanks for that.  Lots of options.  I tried the Ardu approach with 
drones (Arducopter) and the tinkering overhead was horrendous, highly 
experimental.  I gave up and got a DJI that was stable out of the box.  
Lots of CrazyGlu for the Arducopter!


I would like a good datalogger for my older Sokkia SET3 Total Station, 
however.  Is there an Ardu option there?


-
Cheers, Spring



On 06/Mar/2021 12:12, Greg Troxel wrote:

Springfield Harrison  writes:


Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds
interesting, will have a look.

I have an earlier Emlid Reach (not RS or RS2), which has L1 only, and I
never got it to work well.

Also look at the Ardusimple unit -- but it's more a parts kit than a
system.  You need a way to get RTK reference data in, and a good
antenna.  One approach is Vespucci (OSM editor for Android) as a
datalogger, and the Ardusimple WiFi NTRIP master to get corrections over
the phone's hotspot.

   https://www.ardusimple.com/product/simplertk2b/

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Greg Troxel]

Springfield Harrison  writes:

> Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds
> interesting, will have a look.

I have an earlier Emlid Reach (not RS or RS2), which has L1 only, and I
never got it to work well.

Also look at the Ardusimple unit -- but it's more a parts kit than a
system.  You need a way to get RTK reference data in, and a good
antenna.  One approach is Vespucci (OSM editor for Android) as a
datalogger, and the Ardusimple WiFi NTRIP master to get corrections over
the phone's hotspot.

  https://www.ardusimple.com/product/simplertk2b/


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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Thanks Dan.  See my relies to Kirk and Greg.  The Emlid sounds 
interesting, will have a look.


Thanks again . . . .

-
Cheers, Spring



On 06/Mar/2021 08:03, Dan wrote:
Kirk is spot on. That unit is for GIS use and cannot receive RTK GNSS 
corrections. You will need a survey grade receiver, with RTK 
corrections (or post processed) for better accuracy.


Budget option for cm accuracy is the Emlid Reach RS or RS2

On Sat, 6 Mar 2021 at 23:53, Greg Troxel > wrote:



Springfield Harrison mailto:stellar...@gmail.com>> writes:

> I recently acquired a Trimble GeoXT 2005 Series and am puzzled
by the
> results it produces:
>
> 1. Compared to a variety of "known" points, it consistently records
>    positions that appear to be in error by 1.2 - 1.5 m NW from the
>    known point.
> 2. Points are collected and then mapped in QGIS as NAD83, UTM
Zone 10 N.
> 3. The known points include property survey pins, Government control
>    survey monuments, Total Station survey points derived from the
>    above, other GPS results (Trimble ProXRS) and identifiable
points on
>    orthophotos.
> 4. I'm using SBAS correction in the GeoXT.
>
> It appears to be adding a consistent offset to the GPS result
although
> no offset has been set in TerraSync.
>
> Many thanks for any thoughts on this situation . . . . .

I'm really not clear on what this particular receiver is purporting to
do, but a consistent meter-ish offset smells like an incorrect datum.

If you are using SBAS and in the US, that means WAAS.  So you are
getting results that in some CRS that the list hasn't figured out what
it is, but "ITRF2008 current epoch" is my best guess.  That's
essentially equal to "WGS84(G1762) current epoch".

Those frames are definitely not equal to any flavor of NAD83.

qgis, via proj, will treat "WGS84"  and "NAD83" both as datum
ensembles
and because each ensemble has a low-accuracy member treat them as
equal,
and thus choose a null transform.  IMHO this is the wrong thing to do,
as WGS84(G1762) and NAD83(2011) are both datums with high intrinsic
accuracy and are definitely not  equivalent.

Converting from ITRF2014 to NAD83(2011) will apply a datum shift.

Advice 1 is to shift your project CRS from NAD83 to ITRF2014 and
see if
the relative position of the observations and controls changes. 
 If so,
you have datum transform trouble.

My real advice 2 is to take the data file from the unit and label
it as
ITRF2014, and then see how things line up.  If you are talking about a
meter you need to really pay very close attention not only to datum
labeling but also in understanding the transformations your
software is
making.

Greg
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hello Greg, thanks for your notes.  I think it involves Datum issues, as 
you say.  It seems to be very murky.


My assumption (now it seems likely wrong) was that SBAS (WAAS in 
southern BC?) would "adapt" to the CRS designated in the receiver 
(NAD83, UTN 10N) and was also localized to the field location (as in 
Wide Area).  Thus QGIS would see the resulting NAD83, UTM 10N SHP file 
as compatible with the project CRS in QGIS (EPSG:26910, NAD83 UTM 10N).


I'm not sure why I would need to know or use the SBAS Reference Frame 
although the receiver certainly would.


Changing the project CRS to ITRF2014 (there are 3!, WTF, I used 7912) 
didn't change anything.


I've since deferentially corrected the data with mixed results, some 
better, some worse, relatively.  I need to look at that further.


Anyway, if Pathfinder Office produces a NAD83 UTM 10N SHP file from my 
SSF file (NAD83 UTM 10N), should that not project happily in QGIS set to 
EPSG:26910?  I think the datum transformations would take place in the 
receiver (in concert with SBAS) and Pathfinder Office.


Perhaps there is more to this, I certainly appreciate your thoughts . . . .

-
Cheers, Spring




On 06/Mar/2021 05:53, Greg Troxel wrote:

Springfield Harrison  writes:


I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the
results it produces:

1. Compared to a variety of "known" points, it consistently records
positions that appear to be in error by 1.2 - 1.5 m NW from the
known point.
2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
3. The known points include property survey pins, Government control
survey monuments, Total Station survey points derived from the
above, other GPS results (Trimble ProXRS) and identifiable points on
orthophotos.
4. I'm using SBAS correction in the GeoXT.

It appears to be adding a consistent offset to the GPS result although
no offset has been set in TerraSync.

Many thanks for any thoughts on this situation . . . . .

I'm really not clear on what this particular receiver is purporting to
do, but a consistent meter-ish offset smells like an incorrect datum.

If you are using SBAS and in the US, that means WAAS.  So you are
getting results that in some CRS that the list hasn't figured out what
it is, but "ITRF2008 current epoch" is my best guess.  That's
essentially equal to "WGS84(G1762) current epoch".

Those frames are definitely not equal to any flavor of NAD83.

qgis, via proj, will treat "WGS84"  and "NAD83" both as datum ensembles
and because each ensemble has a low-accuracy member treat them as equal,
and thus choose a null transform.  IMHO this is the wrong thing to do,
as WGS84(G1762) and NAD83(2011) are both datums with high intrinsic
accuracy and are definitely not  equivalent.

Converting from ITRF2014 to NAD83(2011) will apply a datum shift.

Advice 1 is to shift your project CRS from NAD83 to ITRF2014 and see if
the relative position of the observations and controls changes.   If so,
you have datum transform trouble.

My real advice 2 is to take the data file from the unit and label it as
ITRF2014, and then see how things line up.  If you are talking about a
meter you need to really pay very close attention not only to datum
labeling but also in understanding the transformations your software is
making.

Greg

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hi Kirk, thanks for your comments.

Note that the unit is not a Garmin.

My concern is not with the accuracy /per se/ but the systematic 
displacement of the results.  GPS error is usually "random", at least 
over the longer term.


The unit was kept static, 50-60 positions were averaged over 4+ minutes 
and the correction was real time SBAS.  The two readings per site were 
separated in time, code based only.


I've since deferentially corrected the file, results yet to be reviewed.

In a later post, Greg refers to datum issues which I think might be the 
culprit.


Thanks very much . . . .

-
Cheers, Spring



On 06/Mar/2021 03:36, kirk wrote:
That is the limitation of the unit you have. Without using 
differential correction or real time kinematic techniques, that is 
about as good as it gets. You can improve your position a bit by 
keeping the unit static and averaging the 1 hz position data for at 
least 2 minutes. This will give you an average of >120 observations..

A clear view of the sky we also help improve the accuracy.

For post processing work, you will need  unit that records raw rinex 
format data which ghe garmin units typically do not.


Kirk Schmidt



Sent from my Galaxy


 Original message 
From: Springfield Harrison 
Date: 2021-03-06 4:35 a.m. (GMT-04:00)
To: qgis-user 
Subject: [Qgis-user] Trimble GeoXT 2005 Accuracy

Hello All,

I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the 
results it produces:


 1. Compared to a variety of "known" points, it consistently records
positions that appear to be in error by 1.2 - 1.5 m NW from the
known point.
 2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
 3. The known points include property survey pins, Government control
survey monuments, Total Station survey points derived from the
above, other GPS results (Trimble ProXRS) and identifiable points
on orthophotos.
 4. I'm using SBAS correction in the GeoXT.

It appears to be adding a consistent offset to the GPS result although 
no offset has been set in TerraSync.


Many thanks for any thoughts on this situation . . . . .

-
Cheers, Springfield Harrison

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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Dan]

 Kirk is spot on. That unit is for GIS use and cannot receive RTK GNSS
corrections. You will need a survey grade receiver, with RTK corrections
(or post processed) for better accuracy.

Budget option for cm accuracy is the Emlid Reach RS or RS2

On Sat, 6 Mar 2021 at 23:53, Greg Troxel  wrote:

>
> Springfield Harrison  writes:
>
> > I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the
> > results it produces:
> >
> > 1. Compared to a variety of "known" points, it consistently records
> >positions that appear to be in error by 1.2 - 1.5 m NW from the
> >known point.
> > 2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
> > 3. The known points include property survey pins, Government control
> >survey monuments, Total Station survey points derived from the
> >above, other GPS results (Trimble ProXRS) and identifiable points on
> >orthophotos.
> > 4. I'm using SBAS correction in the GeoXT.
> >
> > It appears to be adding a consistent offset to the GPS result although
> > no offset has been set in TerraSync.
> >
> > Many thanks for any thoughts on this situation . . . . .
>
> I'm really not clear on what this particular receiver is purporting to
> do, but a consistent meter-ish offset smells like an incorrect datum.
>
> If you are using SBAS and in the US, that means WAAS.  So you are
> getting results that in some CRS that the list hasn't figured out what
> it is, but "ITRF2008 current epoch" is my best guess.  That's
> essentially equal to "WGS84(G1762) current epoch".
>
> Those frames are definitely not equal to any flavor of NAD83.
>
> qgis, via proj, will treat "WGS84"  and "NAD83" both as datum ensembles
> and because each ensemble has a low-accuracy member treat them as equal,
> and thus choose a null transform.  IMHO this is the wrong thing to do,
> as WGS84(G1762) and NAD83(2011) are both datums with high intrinsic
> accuracy and are definitely not  equivalent.
>
> Converting from ITRF2014 to NAD83(2011) will apply a datum shift.
>
> Advice 1 is to shift your project CRS from NAD83 to ITRF2014 and see if
> the relative position of the observations and controls changes.   If so,
> you have datum transform trouble.
>
> My real advice 2 is to take the data file from the unit and label it as
> ITRF2014, and then see how things line up.  If you are talking about a
> meter you need to really pay very close attention not only to datum
> labeling but also in understanding the transformations your software is
> making.
>
> Greg
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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[Greg Troxel]

Springfield Harrison  writes:

> I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the
> results it produces:
>
> 1. Compared to a variety of "known" points, it consistently records
>positions that appear to be in error by 1.2 - 1.5 m NW from the
>known point.
> 2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
> 3. The known points include property survey pins, Government control
>survey monuments, Total Station survey points derived from the
>above, other GPS results (Trimble ProXRS) and identifiable points on
>orthophotos.
> 4. I'm using SBAS correction in the GeoXT.
>
> It appears to be adding a consistent offset to the GPS result although
> no offset has been set in TerraSync.
>
> Many thanks for any thoughts on this situation . . . . .

I'm really not clear on what this particular receiver is purporting to
do, but a consistent meter-ish offset smells like an incorrect datum.

If you are using SBAS and in the US, that means WAAS.  So you are
getting results that in some CRS that the list hasn't figured out what
it is, but "ITRF2008 current epoch" is my best guess.  That's
essentially equal to "WGS84(G1762) current epoch".

Those frames are definitely not equal to any flavor of NAD83.

qgis, via proj, will treat "WGS84"  and "NAD83" both as datum ensembles
and because each ensemble has a low-accuracy member treat them as equal,
and thus choose a null transform.  IMHO this is the wrong thing to do,
as WGS84(G1762) and NAD83(2011) are both datums with high intrinsic
accuracy and are definitely not  equivalent.

Converting from ITRF2014 to NAD83(2011) will apply a datum shift.

Advice 1 is to shift your project CRS from NAD83 to ITRF2014 and see if
the relative position of the observations and controls changes.   If so,
you have datum transform trouble.

My real advice 2 is to take the data file from the unit and label it as
ITRF2014, and then see how things line up.  If you are talking about a
meter you need to really pay very close attention not only to datum
labeling but also in understanding the transformations your software is
making.

Greg


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Re: [Qgis-user] Trimble GeoXT 2005 Accuracy

[kirk]

That is the limitation of the unit you have. Without using differential 
correction or real time kinematic techniques, that is about as good as it gets. 
You can improve your position a bit by keeping the unit static and averaging 
the 1 hz position data for at least 2 minutes. This will give you an average of 
>120 observations.. A clear view of the sky we also help improve the accuracy. 
For post processing work, you will need  unit that records raw rinex format 
data which ghe garmin units typically do not.Kirk Schmidt Sent from my Galaxy
 Original message From: Springfield Harrison 
 Date: 2021-03-06  4:35 a.m.  (GMT-04:00) To: qgis-user 
 Subject: [Qgis-user] Trimble GeoXT 2005 Accuracy 
Hello All,
I recently acquired a Trimble GeoXT 2005 Series and am puzzled by
  the results it produces:

  Compared to a variety of "known" points, it consistently
records positions that appear to be in error by 1.2 - 1.5 m NW
from the known point.  
  
  Points are collected and then mapped in QGIS as NAD83, UTM
Zone 10 N.  
  
  The known points include property survey pins, Government
control survey monuments, Total Station survey points derived
from the above, other GPS results (Trimble ProXRS) and
identifiable points on orthophotos.  
  
  I'm using SBAS correction in the GeoXT.

It appears to be adding a consistent offset to the GPS result
  although no offset has been set in TerraSync.

Many thanks for any thoughts on this situation . . . . .

-
Cheers, Springfield Harrison


  

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[Qgis-user] Trimble GeoXT 2005 Accuracy

[Springfield Harrison]

Hello All,

I recently acquired a Trimble GeoXT 2005 Series and am puzzled by the 
results it produces:


1. Compared to a variety of "known" points, it consistently records
   positions that appear to be in error by 1.2 - 1.5 m NW from the
   known point.
2. Points are collected and then mapped in QGIS as NAD83, UTM Zone 10 N.
3. The known points include property survey pins, Government control
   survey monuments, Total Station survey points derived from the
   above, other GPS results (Trimble ProXRS) and identifiable points on
   orthophotos.
4. I'm using SBAS correction in the GeoXT.

It appears to be adding a consistent offset to the GPS result although 
no offset has been set in TerraSync.


Many thanks for any thoughts on this situation . . . . .

-
Cheers, Springfield Harrison


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