[PROJ] Right way to do this transformation/projection : ITRF2014 -> WGS84 UTM

[Greg Troxel]

Even Rouault <even.rouault at spatialys.com> writes:

. On lundi 30 décembre 2019 13:04:50 CET Julien Schroder wrote:
> Hum, doesn't make sense to me. Can you demonstrate this with PROJ command line 
> utilities ?
>
>> Which surprised me as I thought that going from ITRF2014 to WGS84 involved
>> a step through ITRF2000.

Careful - I think you mean "from ITRF2014 to WGS84(G1762)".  Each WGS84
realization has a separate relationship to various ITRF and NAD83.   I
am not clear if this link is fully correct (although I suspect it is):

  https://www.e-education.psu.edu/geog862/node/1804

One of the earlier WGS84 realizations seems equivalent to ITRF2000.

> How did you see that ? In the above, the first result, which has worldwide 
> validity, goes from ITRF2014 to WGS 84 (G1762) through ITRF2008. Because there 
> is no direct transformation between ITRF2014 and WGS 84 (G1762) in the EPSG 
> dataset (I presume the reason is that WGS 84 (G1762) must have been defined 
> from ITRF2008)

It seems that WGS84(G1762) is defined by station coordinates at a number
of sites that also help to define ITRF2008.  This paper has the details
(and a reference that I have not looked for yet, but seems interesting).

  https://www.unoosa.org/pdf/icg/2016/icg11/wgd/02wgd.pdf

> (*) well, this isn't completely true. If you try
> projinfo -s ITRF2014 -t WGS84 --spatial-test intersects --summary
> with latest PROJ 6.3, you'll get not-null transformations in the USA in the 
> Gulf of Mexico, but I think they are questionable as they involve a lot of 
> hoops through other CRS such as ITRF2008, NAD83(2011), NAD83 and NAD27 ! This 
> is due to latest EPSG database having a complex NAD27->ITRF2014 concatenated 
> operation for Gulf of Mexico (using the NAD83, NAD83(2011) and ITRF2008 
> intermediates), and thus it is chained with transformations from NAD27 to 
> WGS84...

Wow!