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<div>First question: </div>
<div>Does Proj support this local coordinate grid shift?</div>
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<p>What do you mean by local: a grid that deal with projected
coordinates ? Is it really the case here ? (sorry didn't have time
to read thoroughly your links). We've had instances where the data
producer originally provided grids referenced to projected
coordinates, like the OSGB15 geoid model, and the contributor to
PROJ-data reprojected them to geographic coordinates to make them
more usable by PROJ. Of course this only worked for a geoid model.
If the content of the grid itself is shifts in eastings,
northings, then a more complex transformation has to be done.
Otherwise PROJ would need a few changes to deal with grids that
would operate on projected coordinates.<br>
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<div><br>
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<div>Second question:</div>
<div>The Czech Technical University in Prague has a page about
using Proj to transform to/from S-JTSK <a
href="http://freegis.fsv.cvut.cz/gwiki/S-JTSK_/_Grid"
moz-do-not-send="true">here</a> (<a
href="https://freegis-fsv-cvut-cz.translate.goog/gwiki/S-JTSK_/_Grid?_x_tr_sch=http&_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=en&_x_tr_pto=wapp"
moz-do-not-send="true">English</a>). It suggests using grid
shift files from some CZ researchers with the old `nadgrids`
and `geoidgrids` paradigm. </div>
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OK, so "standard grids" here. Are they the same you referred too
previously ?<br>
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<div>would Proj accept a PR for adding these grid shift files to
get the better accuracy?</div>
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<p>I would strongly suggest that you, or more appropriately the
Czech geodesic authority register those grids with IOGP in the
EPSG dataset. That's the main source of geodesic data for PROJ.
Otherwise we need to add custom entries, and this adds a
maintenance burden to the project. If you'd want those grid(s) to
be included in <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ-data/">https://github.com/OSGeo/PROJ-data/</a>, you'll have
also to make sure that they are licensed under an open data
license such as the ones listed in
<a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ-data/#about-the-data-package">https://github.com/OSGeo/PROJ-data/#about-the-data-package</a>. It can
take some time of discussion with the data producer so 1) they are
aware about the existence of licenses 2) they are willing to
distribute under an open data license.</p>
<p>Even<br>
</p>
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cite="mid:CABG=M1M=7n9xjsTsKvxn++iSc8Dxc7=rhhM2bZBVbReSSZggsQ@mail.gmail.com">
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<div>Thanks for reading, and thanks for any advice you can
offer.</div>
<div>Sincerely,</div>
<div>Erixen Cruz</div>
<div>3D Software Developer, <a href="https://cesium.com/"
moz-do-not-send="true">Cesium</a></div>
<div><a href="mailto:erixen@cesium.com" moz-do-not-send="true"
class="moz-txt-link-freetext">erixen@cesium.com</a></div>
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<pre class="moz-quote-pre" wrap="">_______________________________________________
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<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.</pre>
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