[PROJ] bound + compound + derived vertical

[Even Rouault]

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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