[Proj] Understanding deformation model usage

stevejking stevejking at talktalk.net
Wed Mar 7 02:44:43 EST 2018

Yes, that makes sense to me now. But that means those ETRF00 velocities
(with a slight adjustment of position for epoch 2010.00 to 2000.00 should
come close to the realigned NKG velocity grids you have?
But although the z is reasonable, the xy don't look so good. Is it possible
the velocity components have accidentally been transformed (ie. grid values
treated as heights in gdalwarp GDAL 2.2.1 and above)?

I've transformed the Cartesian EPN Stations ETRF00 to long lats at epoch
2000.00 here 


Kristian Evers-2 wrote
> 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
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> Sendt: 28. februar 2018 12:29
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> 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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