[PROJ] bound + compound + derived vertical

[Javier Jimenez Shaw]

Hi

I want to create a WKT2 to define a CRS with some specific conditions.
For context, it is a horizontal (translation, rotation and scale) and
vertical (offset and slope) transformation over a Gauß-Krugger over MGI,
but MGI is defined by the Helmert transformation, and not by the grid file.

To ensure that the Helmert transformation is done, I am creating a BOUNDCRS
with those parameters.
Inside the SOURCECRS I made a Compound with a derived projected and a
derived vertical.
That would allow me to include a proj pipeline with the horizontal
correction, and use the derived vertical (using the Ellipsoid datum) to
apply a vertical offset and slope.

Not a small WKT2, but doable. I just have to copy the parameters I have in
a json in the proper places, and it should work. But no, the vertical
offset and slope is not applied.

Do you know why?

Ok, I thought that I can add the vertical component inside the
derivingconversion of the baseprojcrs. If I add "+step +proj=affine
+zoff=0.55429" it works fine. But I need to add an slope, something like
"+step +proj=vertoffset +lat_0=48 +lon_0=12 +dh=0.55429 +slope_lat=1.234
+slope_lon=0.234"
But no. vertoffset works over a geodetic system, and the deriving
conversion output is a cartersian projected system.

In other examples have seen that the vertoffset pipeline is applied before
the projection. How can I do it? Any idea why is it failing and how can I
work it around?

I can supply some WKT2s with my trials. They are big.

Thank you
Javier

PS If you reached here, I have a present for you: in vscode or vscodium,
you can format a WKT with "ini" format. The brackets are colored, and it
makes easier to detect mistakes.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/proj/attachments/20251113/60a3d3f4/attachment.htm>