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 <stellar...@gmail.com>
Date: 2021-03-08 3:17 p.m. (GMT-04:00)
To: Nicolas Cadieux <njacadieux.git...@gmail.com>
Cc: kirk <k...@nortekresources.com>, Jorge Gustavo Rocha
<j...@geomaster.pt>, qgis-user@lists.osgeo.org, Greg Troxel
<g...@lexort.com>, 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. 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 are using a state correction service,
can you select more stations? How long are the observations? Have
you tried other methods of post processing like PPP?
Have you contacted Trimble? Have you looked on there site to see if
there is a software update (firmware) for the unit or the post
processing software?
Nicolas Cadieux
https://gitlab.com/njacadieux
Le 8 mars 2021 à 05:24, Springfield Harrison <stellar...@gmail.com>
a écrit :
Hi Kirk,
Thanks again for the ideas.
Re "I assume your raw data files are being converted to gpx on a
computer since the raw terrasync files are proprietary binary
files". Not sure why you would make this assumption - PFO does not
export GPX files, only GIS files of many kinds, although one could
create a custom format I suppose.
I have always avoided non-GIS formats (Garmin, GPX, GDB, KML, KMZ,
GoogleEarth, iPad/Tablet "mapping", etc.). I'm in the process of
re-mapping 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 Post 1.44 1.44
SBAS 1.37 1.26 1.33
Uncorr 0.73
0.73
GeoXT Total *1.34* *1.26* *1.32*
ProXR RTCM 0.38 0.61 0.49
ProXR Total *0.38* *0.61* *0.49*
Grand Total *1.17* *0.97* *1.12*
Location Data
*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 Post 9 1492 9 1492
SBAS 8 1280 5 905 13 2185
Uncorr 2 2836
2 2836
GeoXT Total *19* *5608* *5* *905* *24* *6513*
ProXR RTCM 4 2541 4 683 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.
<malbiblkchcpcpdh.png>
As above but with 2 uncorrected GeoXT points overlaid, including the
individual positions that were averaged.
<jpbjaanipeilbbgo.png>
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 <stellar...@gmail.com>
Date: 2021-03-07 5:57 a.m. (GMT-04:00)
To: kirk <k...@nortekresources.com>, Jorge Gustavo Rocha
<j...@geomaster.pt>, qgis-user@lists.osgeo.org, Greg Troxel
<g...@lexort.com>, Dan <19dm...@gmail.com>, Nicolas Cadieux
<njacadieux.git...@gmail.com>
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 <j...@geomaster.pt>
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<stellar...@gmail.com> 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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