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<p>Javier,</p>
<p>PROJ is not smart enough to use datum transformations involving a
projected CRS when doing datum transformations between geographic
CRS, without an explicit record in the database. So here you would
need to add a concatenated transformation record chaining
PROJ:ETRS89_3D_TO_S_JTSK_E_N_BALTIC_HEIGHT with the inverse map
projection of S-JTSK / Krovak East North EPSG:5514</p>
<p>Looking at the cuzk online transformer at
<a class="moz-txt-link-freetext" href="https://geoportal.cuzk.cz/(S(aipi30p34gvo5u3w1xywxga3))/Default.aspx?lng=EN&mode=TextMeta&text=wcts&menu=19">https://geoportal.cuzk.cz/(S(aipi30p34gvo5u3w1xywxga3))/Default.aspx?lng=EN&mode=TextMeta&text=wcts&menu=19</a>
, coordinates in S-JTSK can only be given/returned with the
projected CRS. Perhaps it is not "idiomatic" to use geographic
coordinates in that system.</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 06/10/2025 à 21:29, Javier Jimenez
Shaw via PROJ a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CADRrdKs30B6ygydHj64mnr01YAYTSqJvVwqYAgHs=P2xjthzSw@mail.gmail.com">
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<div dir="ltr">
<div>Hi</div>
<div><br>
</div>
<div>Playing with the latest master in the Czech Republic, I
noticed something strange.</div>
<div>The new grid file cz_cuzk_table_-y-x_3_v1710.tif is used
only if the projected CRS EPSG:5514 is used, but not with its
geographic "parent", S-JTSK EPSG:4156. Well, it is at position
13 on the list of operations.</div>
<div><br>
</div>
<div>Just compare</div>
<div><span style="font-family:monospace">PROJ_NETWORK=ON
./projinfo -o proj --3d EPSG:4258 EPSG:5514+8357
--spatial-test intersects</span></div>
<div><br>
</div>
<div>with</div>
<div><br>
</div>
<div><span style="font-family:monospace">PROJ_NETWORK=ON
./projinfo -o proj --3d EPSG:4258 EPSG:4156+8357
--spatial-test intersects</span></div>
<div><br>
</div>
<div>Doing only 2D transformation, it is even more clear. The
grid file is never used with EPSG:4156</div>
<div><br>
</div>
<div>Does it make sense?</div>
<div><br>
</div>
<div>I know that the grid file is defined in EPSG:5514. But I
assume that the correction applies to the geographic system
transformation, not to the Krovak projection itself.</div>
<div><br>
</div>
<div>Cheers</div>
<div>Javier.</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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</pre>
</blockquote>
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My software is free, but my time generally not.</pre>
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