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

[Julien Schroder]

Hello,
First I want to apologize as this is a bit of a beginner question but after
hours of experimentation I am still confused.

I have coordinates in ITRF2014 (both in geocentric and geodetic
coordinates) with an associated EPOCH which I am trying to
transform/project to WGS84 UTM18N using pyproj/PROJ and EPSG codes. I am
working with surveying data, trying to maximize the accuracy. So far my
group made the approximation that coordinates in ITRF2014 were close enough
to WGS84 to not bother with the transformation but I would like to change
that.

I am looking for advice on how to do this properly :

   - Would you preferably use the geocentric coordinates for the
   transformation/projection?
   - Could I just do something like this :

#with EPSG 7789 +> ITRF2014 geocentric and EPSG 32618 WGS84 UTM18N

transformer = Transformer.from_crs(7789,32618)

X2,Y2, Z2, _ = transformer.transform(xx=X, yy=Y,zz=Z, tt=g.epoch)


During my experimentation I noticed that doing EPSG 7789 => EPSG 32618
holds different results (about 4cm diffrence) than  EPSG 7789  => EPSG 4919
=> EPSG 32614
Which surprised me as I thought that going from ITRF2014 to WGS84 involved
a step through ITRF2000.

In the same way converting between ITRF geocentric (EPSG 7789) and ITRF2014
lat long Height (EPSG 7912) gives me some 7cm differences which confused me
a lot and lead me to ask for help.

As a bonus question, do you know of a tool that support those
transformation and could help me validate my results?

Thanks a lot for your help!
Happy end of the year!
Regards
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