[Proj] Understanding deformation model usage

[Kristian Evers]

Steve,

> Are the Cartesian deformation grids tied to a particular TRF ? I was not
> expecting them to be.

At least for the use case that I developed this for, yes, the grids are tied to a
particular frame.  In case of the Nordic ITRFyy(yy) -> ETRS89 transformations
that frame is ETRF00. That is, it is co-rotating with the Eurasian continental
plate.

The EPN velocities you have linked to are relative to the various frames
in the list. So the ITRF velocities includes the rotation velocity
of the continent but the ETRF velocities doesn't (since the frame itself is defined
as co-rotating with the continent).

Does that make sense to you?

/Kristian

-----Oprindelig meddelelse-----
Fra: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] På vegne af stevejking
Sendt: 28. februar 2018 12:29
Til: proj at lists.maptools.org
Emne: Re: [Proj] Understanding deformation model usage

Kristian,
A follow up question, related to usage,

Are the Cartesian deformation grids tied to a particular TRF ? I was not
expecting them to be. The reason I ask is that on this website:
http://www.epncb.oma.be/_productsservices/coordinates/index.php
Station positions (I assume Cartesian) and velocities are given using three
different reference frames. Drop down list top right you can select
individual stations. Class A have average velocities (to GPS week 1950). And
although the Cartesian coordinates from each TRF don’t differ that much, the
average velocities do?

In the proj documentation example I think it assumes the deformation grids
are not tied to a particular TRF.

Thanks again

Steve



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