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Transformations between various NAD83 and WGS84 realizations

Question asked by henrymogs on Feb 16, 2017
Latest reply on Mar 15, 2018 by joel_cusick

I realize there are already many questions and answers out there related to this issue.  However, I continue having a difficult time pinpointing exactly which transformations I should use. 


Essentially, I have GPS data that was post processed against the local CORS stations in Pathfinder Office using the reference position from base provider option, which depending on the date and station would be ITRF00 or ITRF08 and exported as NAD83 CORS96 and in later years as NAD83 (2011).  Now, I have a Collector app that is using SBAS corrections, so the data is in ITRF 2008 (essentially equal to WGS84 within 10cm/4"), if I'm not mistaken.  This means that I have data in 3 different datums or realizations in regards to the NAD83 GPS points. 


I'm using ArcGIS Desktop 10.3.1, and by looking at the transformations list published with each release of desktop, it appears that the transformations between NAD_1983_HARN, NAD_1983_CORS96, and NAD_1986 (original/1986) are equivalent or simply "bookkeeping".  If this is the case, then there's really no method or transformation in the Project geoprocessing tool that would enable me to reproject my NAD_1983_CORS96 GPS data into NAD_1983_2011, correct?


As far as Collector goes, if the data is coming in as ITRF 2008 based on the SBAS correction source, if I overlay it with NAD_1983_CORS96 or NAD_1983_HARN, etc., what's the best transformation to use? Or does it really not make a difference if they're all treated as equal as far as ArcGIS is concerned? 


Finally, maybe I just haven't come across the details on this yet, but when ESRI references GCS_WGS_1984, which WGS 1984 are they referring to?  Is the reference to G1762, which is the latest realization, or is this in reference to G1674 or G1150? I realize that these are all based on ITRF and should all be within 10cm/4", but I'd like to #1 understand what ESRI is referring to and #2 be able to select the most accurate transformation settings for the data.


Thank you in advance,

Henry M.