[Proj] Proj4 and Epoch

Greg Troxel gdt at ir.bbn.com
Mon Mar 7 20:58:49 EST 2016

barronian <ian at roqc.no> writes:

> Is there support for Epoch in Proj4 ? 
> If so could you please give me a pointer as to how to access the
> functionality? 

That's a really good question.  I've been on this list for a long time
and haven't seen any.

proj4 uses EPSG codes.   I think a question to answer first is how EPSG
codes represent epoch.

For example (US centric :-), NAD 83 has many incarnations, but arguably
the standard one is "NAD83(2011)":

However this doesn't talk about epoch at all.  Arguably coordinates in
EPSG 6318 are epoch 2010.0, following:

But, it's not clear to me how to represent a different epoch, or to talk
about velocities in EPSG or proj4 at all.

So, I suspect you have to transform to the standard epoch in some frame,
and then to another frame, and then to the epoch you want.
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