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<p>Jochem,<br>
</p>
<div class="moz-cite-prefix">Le 24/01/2022 à 20:09, Lesparre, Jochem
via PROJ a écrit :<br>
</div>
<blockquote type="cite"
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<p class="MsoPlainText"><span lang="EN-GB">Dear list,<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">I'm from Netherlands
Partnership Geodetic Infrastructure (NSGI). We published
NTv2 (.gsb) and VDatum (.gtx) grid files for the national
CRS of the Netherlands (RD coordinates with NAP height) in
2019. PROJ converted these to GeoTIFF (.tif) in 2020 [1].
Unfortunately, some wrong information was stored in the
metadata of the GeoTIFF files in the conversion. We are now
creating new GeoTIFF files with corrected metadata, using
the Python scrips ntv2_to_gtiff.py [2] and
vertoffset_grid_to_gtiff.py [3]. <o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">For most changes in
the metadata this is straightforward, but there is one more
difficult issue:<o:p></o:p></span></p>
<p class="MsoPlainText" style="margin-left:35.4pt"><span
lang="EN-GB">We have two variants of the horizontal
transformation:
<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="margin-left:35.4pt;mso-list:l4
level1 lfo5"><span lang="EN-GB">Conventional 1-step
transformation (variant 2): geographic coordinates of
national CRS ---[nl_nsgi_rdtrans2018.tif]---> ETRS89
<o:p></o:p></span></li>
<li class="MsoPlainText" style="margin-left:35.4pt;mso-list:l4
level1 lfo5"><span lang="EN-GB">Better 2-step transformation
(variant 1): geographic coordinates of national CRS
---[nl_nsgi_rdcorr2018.tif]---> corrected geographic
coordinates of national CRS
---[7_parameter_transformation]---> ETRS89<o:p></o:p></span></li>
</ul>
<p class="MsoPlainText" style="margin-left:35.4pt"><span
lang="EN-GB">Since there is no separate EPSG code for the
corrected geographic coordinates of the national CRS, we
want to use the same EPSG code for both corrected and
uncorrected coordinates. Or will it give problems when the
source and target CRS of a GeoTIFF file are the same?</span></p>
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</blockquote>
<p>Instead of the target_crs_code metadata item, you could include a
target_crw_wkt with a WKT2 string. That can be done through the
ntv2_to_gtiff.py script as it can accept a WKT2 CRS string as the
value for --target-crs.<br>
</p>
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cite="mid:AM0P192MB0482A6AD0F1ADD46EEA1312AEF5E9@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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<p class="MsoPlainText" style="margin-left:35.4pt"><span
lang="EN-GB"><o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">Next to this, I have
some other questions:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span
lang="EN-GB">Shouldn't a GeoTIFF grid file for a vertical
transformation have an accuracy band like a grid for a
horizontal transformation? Is it possible with the Python
script to create an accuracy band in the GeoTIFF from a
VDatum grid file?</span></li>
</ul>
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</blockquote>
<p>You could possibly add with GDAL standard tools (gdal_translate,
etc) a band with the accuracy and a description of
"geoid_undulation_accuracy" (you may need to go through a VRT to
manually add the Units to the band). The
validate_vertical_offset_geographic_to_vertical() method of the
check_gtiff_grid.py script would likely have to be updated so that
it doesn't emit an information message about the new band not
being recognized. And the spec at
<a class="moz-txt-link-freetext" href="https://proj.org/specifications/geodetictiffgrids.html">https://proj.org/specifications/geodetictiffgrids.html</a> as well<br>
</p>
<p><br>
</p>
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cite="mid:AM0P192MB0482A6AD0F1ADD46EEA1312AEF5E9@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span
lang="EN-GB"><o:p></o:p>Can I add a
recommended_interpolation_method with the Python scripts?</span></li>
</ul>
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</blockquote>
Not currently. Either enhance them or add the metadata item
manually through GDAL tools (gdal_translate -mo <span lang="EN-GB">recommended_interpolation_method=foo
in.tif out.tif -co COMPRESS=DEFLATE -co INTERLEAVE=BAND -co
PREDICTOR=3</span>). Note that PROJ itself will ignore that item
and always apply bilinear interpolation.<br>
<blockquote type="cite"
cite="mid:AM0P192MB0482A6AD0F1ADD46EEA1312AEF5E9@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span
lang="EN-GB"><o:p></o:p>How should I supply the corrected
GeoTIFF files to PROJ?</span></li>
</ul>
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</blockquote>
Pull request against <span lang="EN-GB"><a
href="https://github.com/OSGeo/PROJ-data/tree/master/nl_nsgi">https://github.com/OSGeo/PROJ-data</a></span>
<blockquote type="cite"
cite="mid:AM0P192MB0482A6AD0F1ADD46EEA1312AEF5E9@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span
lang="EN-GB">Is it necessary for PROJ to use new files
names to distinguish them from the old version with
incorrect metadata?</span></li>
</ul>
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</blockquote>
No<br>
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cite="mid:AM0P192MB0482A6AD0F1ADD46EEA1312AEF5E9@AM0P192MB0482.EURP192.PROD.OUTLOOK.COM">
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<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span
lang="EN-GB"><o:p></o:p></span></li>
</ul>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">Regards, Jochem <o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">[1] <a
href="https://github.com/OSGeo/PROJ-data/tree/master/nl_nsgi"
moz-do-not-send="true">
https://github.com/OSGeo/PROJ-data/tree/master/nl_nsgi</a>
<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">[2] <a
href="https://github.com/OSGeo/PROJ-data/blob/master/grid_tools/ntv2_to_gtiff.py"
moz-do-not-send="true">
https://github.com/OSGeo/PROJ-data/blob/master/grid_tools/ntv2_to_gtiff.py</a><o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">[3] <a
href="https://github.com/OSGeo/PROJ-data/blob/master/grid_tools/vertoffset_grid_to_gtiff.py"
moz-do-not-send="true">
https://github.com/OSGeo/PROJ-data/blob/master/grid_tools/vertoffset_grid_to_gtiff.py</a><o:p></o:p></span></p>
<p class="MsoPlainText"><b><span lang="EN-GB"><o:p> </o:p></span></b></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">J. Lesparre<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB">Netherlands
Partnership Geodetic Infrastructure (NSGI.nl)<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
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<pre class="moz-signature" cols="72">--
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My software is free, but my time generally not.</pre>
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