> So, I agree with you that using the reference epoch, like PROJ does,
is the most reasonable thing to do for the moment.
Just to clarify that if you use a time-dependent Helmert transformation
without specifying an epoch, PROJ will only apply the non-time-dependent
terms. So the "reference epoch" in that situation is the one of the
transformation, not the frame reference epoch of the datum
Cf:
$ echo 1 0 0 | bin/cct +proj=helmert +x=1 +dx=.1 +t_epoch=1234 2.0000
0.0000 0.0000 inf
$ echo 1 0 0 1235 | bin/cct +proj=helmert +x=1 +dx=.1 +t_epoch=1234
2.1000 0.0000 0.0000 1235.0000
PROJ 9.5 has now a new API function,
proj_coordoperation_requires_per_coordinate_input_time(), to indicate
you if a given coordinate operation expects time-dependent terms:
https://github.com/OSGeo/PROJ/pull/4221 .
There's also an explicit error code for the transformations where the
coordinate epoch is really required, so currently +proj=defmodel and
+proj=deformation +t_epoch= . For time-dependent Helmert, this is
considered optional as mentioned above (mostly for backward compatibility)
Even
--
http://www.spatialys.com
My software is free, but my time generally not.
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