Hi Javier,
Do you try to transform from that coumpound of bound to MGI 3D ? If
so,that's probably a limitation in the current implementation of
CoordinateOperationFactory::Private::createOperationsCompoundToGeog().
Around line 6026 of coordinateoperationfactory.cpp, there's a case that
deal with a similar beast but only if transforming to "another CRS whose
datum is not the same as the horizontal datum of the source". That
might be "just" a matter of tweaking that code to remove that
restriction. Or something else :-)
Even
Le 13/11/2025 à 17:26, Javier Jimenez Shaw via PROJ a écrit :
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.
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