[PROJ] Plate motion models

[Steve Riddell]

Thanks, Kristian. And the user application is responsible for deciding which plate is to be used, right? That is, there is currently no code in PROJ to identify the plate model for a particular point, right?
Best,
steve

From: Kristian Evers <kreve at sdfe.dk>
Sent: Monday, February 7, 2022 8:43 AM
To: Steve Riddell <sriddell at geocue.com>; proj at lists.osgeo.org
Subject: RE: Plate motion models

Steve,

This is the original commit message [0] from when the plate motion models were introduced:

Parameters for the plate motion models (PMM) for ITRF2008 and ITRF2014
are added to the ITRF2008/2014 init-files. The PMMs allow coordinates
to be moved back and forward in time in plate fixed reference frames
such as GR96 in Greenland which is defined as ITRF94 at 1996.623<mailto:ITRF94 at 1996.623>.
Transforming an ITRF2014-coordinate to GR96 is done with:

+proj=pipeline +step +init=ITRF2014:NOAM   +t_epoch=1996.623 +t_obs=2017.584
               +step +init=ITRF2014:ITRF94 +t_obs=1996.623

where the first step transforms the coordinate back in time to
ITRF2014 at 1996.632<mailto:ITRF2014 at 1996.632> by using the ITRF2014 PMM. The second step transforms
the ITRF2014 coordinate to ITRF94.

And here's a concrete example using cct:

echo 3496746.5664 743256.4272 5264477.0556 2014.0 | cct +init=ITRF2014:EURA +t_epoch=2022.0

My memory fails me regarding how to set +t_epoch and the coordinate epoch but if you play around with them you should quickly be able to figure out how to set them. Check to see if your output coordinate moves in the direction you expect.

/Kristian

[0] https://github.com/OSGeo/PROJ/commit/403f930355926aced5caba5bfbcc230ad152cf86

From: PROJ <proj-bounces at lists.osgeo.org<mailto:proj-bounces at lists.osgeo.org>> On Behalf Of Steve Riddell
Sent: 7. februar 2022 14:49
To: proj at lists.osgeo.org<mailto:proj at lists.osgeo.org>
Subject: [PROJ] Plate motion models

The data for the ITFR2008 & ITRF2014 plate motion models are delivered with PROJ as init files. From the documentation, 8.7, I think I see how an +init proj string can be used for changing epochs between ITFR frames (e.g. ITRF2000 to ITRF2005), but can someone please give an example of using the plate models? For example, if I have a point in ITRF2000 epoch 2022.1 and I want to use the NOAM plate model to move it to 2010.0, what would be the +init string? I'm assuming cct would be an appropriate application for processing this string?
Thanks for any assistance!
Steve
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20220207/7e544cfe/attachment-0001.html>