No subject

lution must be to include time dependent coordinates systems and epoch tran=
sformation within the software stack, but that is a far reaching change.  I=
 guess it must start in the definition and conversion software.

In the meantime it is possible to use workarounds such as defining custom c=
oordinate systems for specific epochs,  as in the http://proj4.org/htpd.htm=
l approach.

Cheers
Chris

> -----Original Message-----
> From: proj-bounces at lists.maptools.org [mailto:proj-
> bounces at lists.maptools.org] On Behalf Of Greg Troxel
> Sent: Tuesday, 8 March 2016 2:59 p.m.
> To: barronian
> Cc: proj at lists.maptools.org
> Subject: Re: [Proj] Proj4 and Epoch
>
>
> 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 an=
d 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 t=
he
> standard one is "NAD83(2011)":
>   http://epsg.io/6318
>
> However this doesn't talk about epoch at all.  Arguably coordinates in EP=
SG
> 6318 are epoch 2010.0, following:
>   http://geodesy.noaa.gov/CORS/coords.shtml
>
> 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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