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GNNS position on handheld does not correspond to position in field.

  • 1.  GNNS position on handheld does not correspond to position in field.

    Posted 12-11-2023 19:36

    Hello,

    Having an issue with the Trimble Geo7x where the GNSS location on the screen does not correspond to the position in the field. Moreover, I have selected a background file of a property boundary which appears on the screen. However, the GNSS position appears 6 miles away from the property boundary I am standing on. I am unsure of the issue but believe updates may be necessary? Currently the handheld is running the following.

    Terresync

     Version 5.70

    Geo7x handheld

                  Firmware: 6.7.16 (64960)

    GNSS

                  Firmware: v4.12.2

    Any help is appreciated.

    on the left of the screen is the property boundary and to the right is the GNSS position X. I am standing within the property boundary

     



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    Patrick Pegnato
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  • 2.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-11-2023 21:07

    Hello Patrick,

    This could be a coordinate system/datum vs background file calibration issue.

    What do you have configured in TerraSync - Setup - Coordinate System?

    And what kind of background file have you loaded and how was it calibrated?

    If you wished I could have a look at the background file for you.

    Cheers



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    John Winkler
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    Original Message


  • 3.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-12-2023 06:20
    Hey John,

    the coordinate system/datum nominated is as follows:

    Zone: Pennsylvania North 3701
    Datum: NADCON (Conus)

    pretty sure this is the correct coordinate system considering the background files won't upload if the Zone  changed.

    looking into it further i'm starting to get the impression that it is a calibration issue. In the compass app the compass disturbance is high and in the red. I have tried to run a full calibration however I cannot get a tone and it wont allow me to finish a full ration step.

    attached are the background files.

    Thanks for the help!



    Original Message


  • 4.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-12-2023 12:24

    Quote "I'm starting to get the impression that it is a calibration issue. In the compass app the compass disturbance is high and in the red. I have tried to run a full calibration however I cannot get a tone and it wont allow me to finish a full ration step."

    Compass calibration will only affect positions captured using Distance / Bearing Offset workflows (typically using the Laser Rangefinder accessory), compass calibration will not make any difference to GNSS positions - unless you are using LASER, don't bother trying magnetic calibration, it won't affect anything (unless you're trying to use the compass to find a known feature)!



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    Norman Smart
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    Original Message


  • 5.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-12-2023 05:55

    I am just curious, have you tried to do a fast or full calibration on the unit?



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    David Hames
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    Original Message


  • 6.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-18-2023 13:41

    I have tried both calibrations. Now the compass disturbance is in good standing.  However, not sure how to tell if the calibration helped make the GNSS position more accurate as I'm not on the project site anymore. Which leads me to my next question. How can I tell if the files are working and the Geo7x is accurate without being on-site to see if the GNSS position is on the boundary background file. In other words, is there a way to test the files at the office before heading to site? 



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    Patrick Pegnato
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    Original Message


  • 7.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-18-2023 13:52

    Compass calibration will only affect positions which are captured using Distance / Bearing Offset workflows (typically using the Laser Rangefinder accessory), compass calibration will not make any difference to GNSS positions!  And even if your compass calibration was faulty and you did use Distance / Bearing offset, the worst error this could give (assuming the compass bearing is wrong by 180°) is 2 times the rangefinder distance, i.e. a few hundred metres at most.

    Forget about compass calibration, a 6 mile error is likely to be reference frames / coordinate systems or similar, as suggested by Joel and by John



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    Norman Smart
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    Original Message


  • 8.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-12-2023 07:36

    You have the current OS, and TerraSync is a bit outdated (5.7 should be up to 5.86) but you have a bigger problem.

    You don't want to use NADCON at all.  That maybe a carry over if your land status layers are in NAD27, but you'll want to do some projecting before you create background data for a modern handheld like this.

    Best to use GIS, and convert your survey data to "WGS84" datum.   Project tools in ESRI will use NADCON from 27 to 84 (not great conversion, but your only choice).  Then once your data is converted, create background (vectors) in PFO (suspect your using that right?).   Switch TerraSync to the default Setup/coordinate system.    I also surmise, you enabled WAAS (SBAS). Thats your best shot at navigating to data in the background.  Message me if you want.



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    Joel Cusick
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    Original Message


  • 9.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-13-2023 01:37
    Hi Patrick,
    For some reason I can't see your background files, another option could be to send them direct to the email address in my profile.
     
    As it's quite possible the files are positioning in the wrong place you might need to also give me some detailed data to locate the actual property. 
     
    I can have a go at reprojecting the file for you - including to WGS84 as Joel has suggested or NAD83 if you wanted to configure that in your PFO & Geo7X - but as already mentioned the NADCOM transformation is going to be a bit rubbery right away and potentially far more so if either the background files and/or property are lost in space.
     
    Cheers


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    John Winkler
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    Original Message


  • 10.  RE: GNNS position on handheld does not correspond to position in field.

    Posted 12-21-2023 04:05
    Hello Patrick,
     
    Confirming I did experience some strange datum / .prj file issues (in my case ending up in the ocean) and I've sent back to your email address the details & files for 3 options that at least for me will now position fine on your property. If any further issues just go for the WGS84 Lat Lon reprojected set, it should be bulletproof.
     
    Cheers


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    John Winkler
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    Original Message