[Qgis-user] Trimble GeoXT 2005 Accuracy

kirk kirk at nortekresources.com
Tue Mar 9 04:32:25 PST 2021


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 <stellargps at gmail.com> Date: 2021-03-08  3:17 p.m.  (GMT-04:00) To: Nicolas Cadieux <njacadieux.gitlab at gmail.com> Cc: 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> 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 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:
            
              Site is open sky but with house and trees adjacent
              Antenna is static, occupation periods long (5 sec logging
        interval)
              32 observations 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 <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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