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Why are my data collector points shifted southwest of my survey point?

Question asked by lmawhinney2175 on Aug 23, 2019
Latest reply on Mar 10, 2020 by mbrady@agreserves.com_AgReserves



Our current process is to use high accuracy Trimble R2 GPS units with a NTRIP connection to local CORS stations here in Tucson, AZ.  The horizontal accuracy is falling anywhere between 1 and 5 inches. We had our Survey team collect a set of data points so that we use this for comparison.  When comparing the Trimble points to the survey points, they are within a range of 1 to 5 inches.  Anything less than 6 inches is acceptable for us.  However, we are also experience lost connections from time to time. 


So, I am testing out Trimble's RTX Field Point product as an alternative.  The fix time is anywhere from 2 to 5 minutes.  The horizontal accuracy reported back is generally 3.9 inches. The mobile device is a samsung galaxy S8.   My web map layers have a WKID projection of 3857.  So I set the collector for ArcGIS (classic) location profile as:


GNSS Receiver Coordinate System: GCS ITRF 2008

Map Coordinate System: WGS 1984 Web Mercator Auxiliary Sphere

Datum Transformation: itrf_2008_to_nad_1983_2011 + wgs_1984_(itrf08)_to_nad_1983-2011


When I bring the points collected while using Trimble's RTX field point product into ArcPro they (green pts) are all consistently shifted west and south to the survey points (yellow).  This leads me to think that I am not doing something right rather than an issue with the unit or the RTX.  Attached is a screen shot of the location profile and of the points compared to the surveyed location with a one foot buffer.  I am thinking it may be the profile, but I am not sure what else to use.


If anyone has an idea of what is going on, I would really appreciate your thoughts, ideas and suggestions.