Replies

• 

  Arnel M. Domag June 13, 2011 at 9:33pm

  Hi ASIF!

  You can find it in many Satellite Positioning System (GPS/GNSS) literatures that vertical accuracy is always twice the horizontal accuracy. If your GPS/GNSS sensors is capable to hit 5mm accuracy in horizontal position, then your vertical accuracy shall be 10mm.

  Hope this helps.

  Regards,

  Arnel M. Domag

  nth geographics and geometrics
  • 

    joseph Uy > Arnel M. Domag June 17, 2011 at 2:45am

    HI Guys, Far distance from reference stn is not a matter for the accuracy of elevation it depends always the accuracy of the instruments used and the procedure applied. For GPS survey of static method of observation, usually error in plane coordinates is doubled in vertical accuracy. Survey grade GPS instruments is capable of 1-5 cms accuracy in horizontal accuracy. GPS elevations are in ellipsoidal height reference but for me I prefered the Mean sea level datum.Usually differential leveling is run to the control stns, this will eliminate corrections in curvature. IM still not convince on the accuracy of GPS elevations thats why I always use Mean sea level as the vertical datum.For planning and design, Civil engineers will always use levels instrument for elevations observation.I do not know if some used GPS elevations.
    • 

      Arnel M. Domag > joseph Uy June 18, 2011 at 11:55am

      To my opinion, mean sea level datum is only good if geoid model for the place you are surveying is available at your disposal. Employing the universal geoid model (EGM96) does not necessarily provide same as or similar to the local geoid model. Yes, I agree that providing vertical control using levels is good for civil engineering requirements but pardon me if I don't get the idea of providing level grade elevation values to control points eliminating curvature correction requirement. Curvature correction is a way of life in survey/mapping work in any discipline you are involved in particularly the civil engineering domain of huge area coverage. 

      I am pretty convinced with my Leica GS09 GNSS ellipsoidal height output values. I can get elevation accuracy of 6mm + 0.5ppm. I don't think this can be beaten easily by levels on long routes granting you are able to perform Laplace correction for the undulations to get the relationship between geoid and ellipsoid models you are employing.