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<div class="moz-cite-prefix">Le 10/11/2021 à 19:12, Javier Jimenez
Shaw a écrit :<br>
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<div>Hi</div>
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<div>In proj.db there is a table "geoid_model" with the list of
accepted GEOIDMODEL tags, like GEOID18, GEOID12B, OSGM15 or
GGM10 (I added that last one because because it is used with
NAVD88 height, for consistency)<br>
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<div><a
href="https://github.com/OSGeo/PROJ/blob/04928472dbee772b6b31c78352dc486fb6543a91/data/sql/customizations.sql#L241"
moz-do-not-send="true">https://github.com/OSGeo/PROJ/blob/04928472dbee772b6b31c78352dc486fb6543a91/data/sql/customizations.sql#L241</a></div>
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<div>However there are many geoid grid files in PROJ-data that
do not have a geoid model name there.<br>
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<div>What is the policy to set geoid models there in that table?</div>
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That's a good question... I guess when there's a well accepted name
for the geoid.<br>
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cite="mid:CADRrdKsQvE-DY02N0WjmSFB8a9bEmTg22gMMhgZOR3_H=2i04Q@mail.gmail.com">
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<div>I already have a patch for that table with many of them,
like AUSGeoid2020, DNN, EGM08-REDNAP, RAF09, RAF18,
NZGeoid2016 or SAGEOID2010. By the way, we use them to "know"
that there is a grid file for a vertical CRS using <a
href="https://proj.org/development/reference/functions.html#c.proj_get_geoid_models_from_database"
moz-do-not-send="true">https://proj.org/development/reference/functions.html#c.proj_get_geoid_models_from_database</a></div>
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This is a bit fragile. I'm not sure I have a solution with the
existing API to propose though. You could issue a raw query to the
database in the grid_transformation table with the source/target CRS
being your vertical CRS.<br>
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<div>Does it make sense to add that to the PROJ repository? If
yes, would it make sense that any new geoid grid file added in
PROJ-data adds a geoid model there?<br>
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Not a big fan of this<br>
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<div>See that this is the tag GEOIDMODEL in WKT2 (if I
understood correctly) so it should not change "so often".<br>
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<div>I do not know how sensible it would be to changes in EPSG
database.<br>
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<p>We're actually using the GEOIDMODEL node of WKT2 differently from
what EPSG does (I think I realized that after it was already
implemented in PROJ)</p>
<p>In EPSG, GEOIDMODEL is just a reference to one or several
transformations between the vertical CRS and geographic CRS. So
the names are the ones of the transformations, like "<a>WGS 84 to
EGM2008 height (1)". The GEOIDMODEL[] node was initially
included in the WKT2 output, but EPSG changed their policy, and
it is no longer in the output on epsg.org(I've already forgotten
the reason). See https://epsg.org/crs_3855/EGM2008-height.html
that references 2 geoid models but
https://epsg.org/crs/wkt/id/3855 doesn't include them.</a></p>
<p><a><br>
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<div>Thanks.<br>
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<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">.___ ._ ..._ .. . ._.
.___ .. __ . _. . __.. ... .... ._ .__<br>
Entre dos pensamientos racionales <br>
hay infinitos pensamientos irracionales.<br>
<br>
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