[PROJ] GRS80 ellipsoid off-center

[Brian Shaw]

As others of stated it is the same ellipsoid, only the origin of the 
ellipsoid is being shifted 2.2 meters to what is considered the center 
of mass today (what ITRF determines).  While NAD 83 and the original 
WGS84 were off center, 2.2 meters was not bad considering this was 
mostly determined using Doppler and other measurements prior to GPS.

As for your projection parameters I believe you are referencing SPCS 
changes coming with NSRS Modernization.   Assuming so you would be 
interested to know that SPCS2022 will now develop the projections based 
on the surface of land where SPCS83 was developed on the ellipsoid.  
Many states are planning to develop (or already have) Low Distortion 
Projections for their states in addition to the zones NGS will develop.

Addition resources about SPCS:

Home page with links to many maps and data:
https://geodesy.noaa.gov/SPCS/index.shtml

The State Plane Coordinate System History, Policy, and Future Directions
https://geodesy.noaa.gov/library/pdfs/SP_NOS_NGS_13.pdf

2 most recent Recorded Webinars on SPCS
https://geodesy.noaa.gov/web/science_edu/webinar_series/guide-customizing-spcs-2022.shtml
https://geodesy.noaa.gov/web/science_edu/webinar_series/state-plane-coordinates-3.shtml

Cheers
Brian

On 2/7/2020 3:10 PM, Even Rouault wrote:
> On vendredi 7 février 2020 19:44:23 CET Clifford J Mugnier wrote:
>> No.  Same ellipsoid, same name.  Different DATUMS, different names.
> Indeed. And those will be time-dependent datums.
>
> All details in
> https://geodesy.noaa.gov/library/pdfs/NOAA_TR_NOS_NGS_0062.pdf
> https://geodesy.noaa.gov/library/pdfs/NOAA_TR_NOS_NGS_0064.pdf
> https://geodesy.noaa.gov/PUBS_LIB/NOAA_TR_NOS_NGS_0067.pdf
>

-- 
*************************************
Brian Shaw
Geodesist
NOAA/NOS/National Geodetic Survey
Phone # 240-533-9522