[gdal-dev] Issue with Custom Transformation Pipeline in GDALReprojectImage

[Even Rouault]

Martin,

GDALReprojectImage() expects that a correct geotransform is already set 
on the target dataset.

You may use GDALSuggestedWarpOutput2() to get a guessed geotransform

Otherwise for full automated way, you may also using the C function 
GDALWarp().

By the way, your below pipeline looks wrong

|+proj=pipeline +step +inv +proj=krovak +lat_0=49.5 
+lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999 +x_0=0 +y_0=0 
+ellps=bessel +step +inv +proj=hgridshift 
+grids=Slovakia_JTSK03_to_JTSK.gsb +step +proj=krovak +lat_0=49.5 
+lon_0=24.8333333333333 +alpha=30.2881397527778 +k=0.9999 +x_0=0 +y_0=0 
+ellps=bessel +step +proj=webmerc |

After the 3rd step (+proj=krovak), you are in projected coordinate 
space. Applying +proj=webmerc afterwards doesn't make any sense since 
the later expects geographic coordinates. You probably want to omit the 
3rd step

Even

Le 09/01/2025 à 09:20, Martin Ždila via gdal-dev a écrit :
> Dear GDAL developers and users,
>
> I am facing an issue where a custom transformation pipeline defined 
> using PROJ's +proj=pipeline is not being applied when using 
> GDALReprojectImage. The pipeline appears in the debug logs 
> (PROJ_TRACE), but the output image does not reflect the expected 
> transformation.
>
> I have described the issue in detail on StackOverflow, including my 
> code and debugging observations:
> https://stackoverflow.com/questions/79341829/why-is-my-custom-transformation-pipeline-not-applied-with-gdalreprojectimage
>
> If anyone has insights into what might be going wrong or how to 
> resolve this, I would greatly appreciate your help.
>
> Thank you!
> Best regards,
> -- 
> Martin Ždila
>
>
> _______________________________________________
> gdal-dev mailing list
> gdal-dev at lists.osgeo.org
> https://lists.osgeo.org/mailman/listinfo/gdal-dev

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