[PROJ] Affine transformation in proj < 6?

[Thomas Knudsen]

If the 3x3 matrix describes a pure rotation you could probably use
proj=helmert. If it includes shear, I think you are short of luck

Den tor. 12. dec. 2019 kl. 13.31 skrev Tammo Jan Dijkema <
t.j.dijkema at gmail.com>:

> Hi all,
>
> I'm new to proj, so sorry if this is a trivial question (I've read through
> docs for an hour without finding an answer, so it can't be too trivial).
>
> I have a custom coordinate system, which is defined through an affine
> transformation from ETRS89. All coordinates I care about are in xyz
> Cartesian coordinates. In particular, to get pqr coordinates, I do
>
> coords_pqr = (coords_etrs - pqrorigin_etrs) * (3x3 matrix)
>
> Now I'm generating raster images in PQR, which I would like to store in
> GeoTiff, so if I understand correctly I need to write a proj string into
> the GeoTiff to describe the projection. More background: I'm writing the
> PQR-images in python, and want to export them so that I can load them into
> QGIS, with appropriate coordinates.
>
> I see that an affine transformation is part of proj6, but I cannot expect
> users to have that installed. Is there a way to abuse another projection to
> achieve the same thing?
>
> If there is another channel to ask this question, please let me know.
> Thanks in advance!
>
> Tammo Jan Dijkema
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