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<p>Martin,</p>
<p>GDALReprojectImage() expects that a correct geotransform is
already set on the target dataset.</p>
<p>You may use GDALSuggestedWarpOutput2() to get a guessed
geotransform<br>
</p>
<p>Otherwise for full automated way, you may also using the C
function GDALWarp().</p>
<p>By the way, your below pipeline looks wrong<br>
</p>
<pre><code>+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
</code>
</pre>
<p>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<br>
</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 09/01/2025 à 09:20, Martin Ždila via
gdal-dev a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CAL520RkNCOTpyyJEJtvZ6yz5Ttan-WbwUZg8TD=GuRO+eEcovA@mail.gmail.com">
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<div dir="ltr">
<div>Dear GDAL developers and users,<br>
<br>
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.<br>
<br>
I have described the issue in detail on StackOverflow,
including my code and debugging observations:<br>
<a
href="https://stackoverflow.com/questions/79341829/why-is-my-custom-transformation-pipeline-not-applied-with-gdalreprojectimage"
moz-do-not-send="true" class="moz-txt-link-freetext">https://stackoverflow.com/questions/79341829/why-is-my-custom-transformation-pipeline-not-applied-with-gdalreprojectimage</a><br>
<br>
If anyone has insights into what might be going wrong or how
to resolve this, I would greatly appreciate your help.<br>
<br>
Thank you!<br>
Best regards,</div>
<span class="gmail_signature_prefix">-- </span><br>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">
<div dir="ltr">
<div>Martin Ždila <br>
<br>
</div>
</div>
</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
<a class="moz-txt-link-freetext" href="http://www.spatialys.com">http://www.spatialys.com</a>
My software is free, but my time generally not.
Butcher of all kinds of standards, open or closed formats. At the end, this is just about bytes.</pre>
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