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Calibrating Height at Ground

  • 1.  Calibrating Height at Ground

    Posted 12-14-2019 23:12

    Monday I did a job with GCP's that has already been surveyed by a Trimble R8. The BM that they shot was 979.469 ft on NAD83 (2011). I set the Catalyst to the same in TMM. But I was 111.8 ft off. Has anyone put in a negative number in for the Antenna Height and it work? Or has anyone compared numbers to a calibrated system? 



  • 2.  Re: Calibrating Height at Ground
    Best Answer

    Posted 01-06-2020 01:40

    Hi Austin, 

     

    sorry for the delay here - the holiday season...

    The survey you performed with the Trimble R8 - which software did you use here?

    A height offset of 111.8 sounds like an applied geoid. 

     

    GCP (and/ via) TMM apply a time dependent datum transformation which adjust for stuff like tectonic plate movement - TMM does not apply geoids at the moment. 

    Those adjustments are important if you mix correction sources - like SBAS and/ or Trimble RTX and/ or VRS/ RTK stuff. 

     

    The system NAD83 is a composition of things - if you go here: EPSG Geodetic Parameter Registry  and search for 'NAD83' you'll find a whole lot of matches plus. If you open one of those (say EPSG::6319) you'll see a section about 'Geodetic Datum' and potentially (depending on the epsg) an applied geoid. 

    I'd guess you have an applied geoid while GCP provides ellipsoidal heights.

     

    Regards

    Nico