[PROJ] Seeking clarification on PROJ support for temporal transformations

[Nyall Dawson]

Hi Proj list!

I'm seeking some clarification on the current status in PROJ regarding
handling of 4d time-based coordinate transformations. My understanding
is that PROJ v6 supports this (at least for some transformation
types), but I'm unsure to what level.

So, my initial questions are:

- are you aware of any client applications (outside of those provided
with PROJ) which are currently utilising 4d transformations?

- how complete is PROJ's implemention of ISO 19111? If I have a WKT2
definition including epoch information, is PROJ able to read this and
utilise it to perform 4d transforms? Does current PROJ c api allow
retrieval of epoch information from a CRS object? (I can't see which
method would do this in the API reference). And conversely, if you
wanted to create a CRS object coinciding to a particular epoch, would
you need to manually hand-craft a WKT2 string encapsulating this?

- (more on the gdal side, but..) does any existing data format support
WKT2, and in particular, would allow a dataset to be referenced with
an epoch based CRS definition?

Cheers,
Nyall