[Qgis-user] Trimble GeoXT 2005 Accuracy
Springfield Harrison
stellargps at gmail.com
Mon Mar 8 11:16:59 PST 2021
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 <stellargps at 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 <stellargps at gmail.com>
>>> Date: 2021-03-07 5:57 a.m. (GMT-04:00)
>>> To: kirk <kirk at nortekresources.com>, Jorge Gustavo Rocha
>>> <jgr at geomaster.pt>, qgis-user at lists.osgeo.org, Greg Troxel
>>> <gdt at lexort.com>, Dan <19dmb83 at gmail.com>, Nicolas Cadieux
>>> <njacadieux.gitlab at 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 <jgr at geomaster.pt>
>>>> Date: 2021-03-06 6:41 p.m. (GMT-04:00)
>>>> To: qgis-user at 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<stellargps at 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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>>>>> Qgis-user at lists.osgeo.org
>>>>> List info:https://lists.osgeo.org/mailman/listinfo/qgis-user
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>>>> --
>>>> Email Signature
>>>> Logo <https://www.geomaster.pt>
>>>> *Geomaster*
>>>> *Jorge Gustavo Rocha* | Software Engineer
>>>> *e:*jgr at geomaster.pt | *m:*+351 910 333 888
>>>> *g:*41.54094,-8.40490 | *v: *510 906 109
>>>> *a: * Rua António Cândido Pinto, 67, 4715-400 Braga
>>>>
>>>>
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