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<div class="moz-cite-prefix">Le 17/03/2023 à 15:44, Lesparre, Jochem
a écrit :<br>
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cite="mid:AM6P192MB0488DAC40BFF06A0CA6858E7EFBD9@AM6P192MB0488.EURP192.PROD.OUTLOOK.COM">
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<p class="MsoPlainText" style="margin-left:70.8pt"><span
lang="EN-GB">I wrote:<o:p></o:p></span></p>
<p class="MsoPlainText" style="margin-left:70.8pt"><span
lang="EN-GB">> To prevent users to make different choices
in similar use cases, the documentation should indicate what
to do for Lowest Astronomical Tide (LAT) or other Chart
Datum grids.<o:p></o:p></span></p>
<p class="MsoPlainText"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoPlainText" style="margin-left:35.4pt"><span
lang="EN-GB">ER wrote:<o:p></o:p></span></p>
<p class="MsoPlainText" style="margin-left:35.4pt"><span
lang="EN-GB">> Cf <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ/pull/3668">https://github.com/OSGeo/PROJ/pull/3668</a>
+ <a class="moz-txt-link-freetext" href="https://github.com/OSGeo/PROJ-data/pull/97">https://github.com/OSGeo/PROJ-data/pull/97</a><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">Thanks! This means
that the Geodetic TIFF Grid for Chart Datum of Norway (and
possibly also the one of Denmark that Kristian Evers is
working on) wrongly use type
VERTICAL_OFFSET_VERTICAL_TO_VERTICAL instead of
VERTICAL_OFFSET_GEOGRAPHIC_TO_VERTICAL. But as that works
too, it’s not a big deal.<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 have two questions:<o:p></o:p></span></p>
<ul style="margin-top:0cm" type="disc">
<li class="MsoPlainText"
style="margin-left:-18.0pt;mso-list:l0 level1 lfo1"><span
lang="EN-GB">Are you sure about the tag “hydroid_height”?
A Google search (<a
href="https://www.google.com/search?q=%22hydroid+height%22"
moz-do-not-send="true" class="moz-txt-link-freetext">https://www.google.com/search?q=%22hydroid+height%22</a>)
gives only 1 relevant hit. I have no opinion on this, as
it is not my expertise. I’m just helping the people at our
hydrographic service. <br>
</span></li>
</ul>
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</blockquote>
This is borrowed from the GGXF draft
(<a class="moz-txt-link-freetext"
href="https://raw.githubusercontent.com/opengeospatial/CRS-Gridded-Geodetic-data-eXchange-Format/master/specification/GGXF%20v1-0%20OGC-22-051r2_2023-01-09.pdf">https://raw.githubusercontent.com/opengeospatial/CRS-Gridded-Geodetic-data-eXchange-Format/master/specification/GGXF%20v1-0%20OGC-22-051r2_2023-01-09.pdf</a>).
I assume they are right, as they are much smarter people than me.
They have a slightly different naming convention "hydroidHeight"
which I modified to match our convention.<br>
<blockquote type="cite"
cite="mid:AM6P192MB0488DAC40BFF06A0CA6858E7EFBD9@AM6P192MB0488.EURP192.PROD.OUTLOOK.COM">
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<li class="MsoPlainText"
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lang="EN-GB"><o:p></o:p></span><br>
</li>
<li class="MsoPlainText"
style="margin-left:-18.0pt;mso-list:l0 level1 lfo1"><span
lang="EN-GB">Why limit the description to only predefined
options? I can imagine that one could want to use a
reference surface that is not a geoid nor a hydroid, for
example an ellipsoidal DTM grid to transform to/from Above
Ground Level heights. So it might be easier to allow any
description to prevent future problems.</span></li>
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</blockquote>
<p>Well, no, we must have a predefined and limited list. Otherwise
PROJ grid interpolation code, when inspecting a GeoTIFF dataset,
will not know in which channel to find the information.</p>
<br>
<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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