[PROJ] Helmet transform between 2 ITRF sets of coordinates

[Alain Orsoni]

Hello,

I’m trying to convert ITRF92 (epoch 93.0) coordinates to ITRF2014 epoch 2023.0.
Having some 8 cms per year movement I expect some 2.4m difference in the coordinates.

I tried some syntaxes but did not understand clearly how (where) to indicate the epochs (initial and final) in my tests :

One test applied was :

echo -139.57736536  -8.95162075     2.234 2023.0 | cct +proj=pipeline +step +proj=cart +ellps=GRS80 +step +proj=helmert +x=-0.0154 +y=-0.0015 +z=0.0708 +rx=0 +ry=0 +rz=-0.00026 +s=-0.00309 +dx=-0.0001 +dy=0.0005 +dz=0.0033 +drx=0 +dry=0 +drz=-2e-05 +ds=-0.00012 +t_epoch=1993 +convention=position_vector +step +inv +proj=cart +ellps=GRS80

Which gave me 
-139.5773658008   -8.9516192265        2.1701     2023.0000

As result. Difference much lower than expected representing some 20 cm variation from one epoch to the other.

I indicated the final epoch desired in my input and the initial epoch in the helmert transform.
This is probably false, but I did not encounter this kind of indication in the documentation.

Where is the misunderstanding?

Thank you for any help,

Alain Orsoni
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