[PROJ] Seeking clarification on PROJ support for temporal transformations

[Joel Haasdyk]

Indeed, 

Any regular tectonic plate motion can be expressed as a 3 parameter Euler Pole, which can in turn be expressed in the familiar Helmert 14 (15) parameter transformation format, as three Cartesian axial rotation rates (all other components equal 0).
See https://geodesy.noaa.gov/PUBS_LIB/NOAA_TR_NOS_NGS_0062.pdf
See http://www.quickclose.com.au/StanawayetalREFAGppt.pdf 

Case in point are these:
EPSG:: 8049 GDA2020 <=> ITRF2014, with reference epoch 2020.0)
EPSG::8448 GDA2020 <=> WGS84(G1792), with 'parameter reference epoch' @2020.0)
Where GDA2020 is essentially a snapshot of ITRF2014 at 2020.0.

So EPSG can and does publish time-dependent transformations... 
(this is not new, e.g. EPSG::8078 ITRF2000 <=> ITRF2014 for example)
...just not (yet) explicitly from CRS_A(@epoch1) to CRS_A(@epoch2). I could be wrong. 
However... EPSG::8049 gives you all the info you need to transform from 
ITRF2014(@epoch1) <=> ITRF2014(@2020.0) <=> ITRF2014(@epoch2)

Joel Haasdyk

------------------------------

Message: 5 from Digest 20
Date: Wed, 28 Aug 2019 00:50:14 +0300
From: Even Rouault <even.rouault at spatialys.com>
To: Kristian Evers <kreve at sdfe.dk>
Cc: Nyall Dawson <nyall.dawson at gmail.com>, PROJ <proj at lists.osgeo.org>
Subject: Re: [PROJ] Seeking clarification on PROJ support for temporal
	transformations
Message-ID: <2096164.pDk9JYgsY7 at even-i700>
Content-Type: text/plain; charset="us-ascii"

> 
> A global plate motion model is part of ITRF2014 [0]. It comes in the form of
> 
 Euler pole rotation parameters. They can be used in a time-dependent
> Helmert Transformation. Some time ago I included all the parameters in the
> ITRF2014 init file [1]. I use them to transform data from ITRF2014 to the
> local Greenlandic frame GR96 (effectively ITRF94 at 1996.623). I've defined a
> pipeline like this: 
> proj = pipeline ellps = GRS80
>             step inv init = ITRF2014:ITRF94 t_obs = 1996.623
>             step inv init = ITRF2014:NOAM   t_epoch=1996.623
> 

----
Also copied from Archive:
>Even Rouault even.rouault at spatialys.com 
>Tue Aug 27 08:26:57 PDT 2019
>
>That would probably be the best solution.
>
>> Is this being blocked by
>> the EPSG registry itself and lack of means of encapsulating the
>> transformation parameters?
>
>Good questions. I dont't have definite answers.
>The EPSG registry doesn't publish time-dependent transformations for CRS A to 
>CRS A currently, except for the Canadian NAD83(2011) CRS. Not sure if this is 
>a lack of interest, or data, or just that this isn't yet done, but will come 
>in future releases of the database.

>I've heard there are global plate motions models, but haven't investigated 
>what they look like (grids, parametric models... ?) and if they are available 
>for "free". Otherwise you could also have models using methods like Helmert on 
>a per-area basis.

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