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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?<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?<o:p></o:p></span></li><li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span lang="EN-GB">Can I add a recommended_interpolation_method with the Python scripts?<o:p></o:p></span></li><li class="MsoPlainText" style="mso-list:l0 level1 lfo3"><span lang="EN-GB">How should I supply the corrected GeoTIFF files to PROJ?<o:p></o:p></span></li><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?<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">
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">
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">
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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