[PROJ] Seeking clarification on PROJ support for temporal transformations

[Even Rouault]

> 
> A global plate motion model is part of ITRF2014 [0]. It comes in the form of
> 
 Euler pole rotation parameters. They can be used in a time-dependent
> Helmert Transformation. Some time ago I included all the parameters in the
> ITRF2014 init file [1]. I use them to transform data from ITRF2014 to the
> local Greenlandic frame GR96 (effectively ITRF94 at 1996.623). I've defined a
> pipeline like this: 
> proj = pipeline ellps = GRS80
>             step inv init = ITRF2014:ITRF94 t_obs = 1996.623
>             step inv init = ITRF2014:NOAM   t_epoch=1996.623
> 

That's interesting !

I believe there's a small mistake in the ITRF2014 file (or the IGN page might 
have been updated in the meantime) for the ITRF2014:ITRF94 entry. It lacks a 
+drz=0.00002 (the ITRF96 entry as well). I can see it in http://itrf.ign.fr/
doc_ITRF/Transfo-ITRF2014_ITRFs.txt and it is also there in the EPSG dataset:

$ projinfo -s ITRF2014 -t ITRF94 -o PROJ -q
+proj=pipeline +step +proj=axisswap +order=2,1 +step +proj=unitconvert 
+xy_in=deg +xy_out=rad +step +proj=cart +ellps=GRS80 +step +inv +proj=helmert 
+x=-0.0074 +y=0.0005 +z=0.0628 +rx=0 +ry=0 +rz=-0.00026 +s=-0.0038 +dx=-0.0001 
+dy=0.0005 +dz=0.0033 +drx=0 +dry=0 +drz=-2e-05 +ds=-0.00012 +t_epoch=2010 
+convention=position_vector +step +inv +proj=cart +ellps=GRS80 +step 
+proj=unitconvert +xy_in=rad +xy_out=deg +step +proj=axisswap +order=2,1

(the signs are different due to EPSG having ITRF94 to ITRF2014 natively, and 
thus PROJ applying a +inv)

Another detail: the pipeline you mention above is from GR96 to ITRF2014, right 
(due to the 'inv' of ITRF2014:ITRF94) ?
And the last step which I assume is for the northamerica plate motion doesn't 
seem to have any effect as you forced t_obs in the previous step to the 
t_epoch of that step, so the time difference is 0.


$ echo " 2768773.7909  -1598552.2935  5500477.1338" | src/cct +proj=pipeline 
+ellps=GRS80 +step +inv +init=ITRF2014:ITRF94 +t_obs=1996.623
 2768773.7710  -1598552.2904  5500477.1757 

$ echo " 2768773.7909  -1598552.2935  5500477.1338" | src/cct +proj=pipeline 
+ellps=GRS80 +step +inv +init=ITRF2014:ITRF94 +t_obs=1996.623 +step +inv 
+init=ITRF2014:NOAM +t_epoch=1996.623
 2768773.7710  -1598552.2904  5500477.1757 

Even

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