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<p>Hi,</p>
<p>good question. To the best of my knowledge, in the official WKT /
WKB spec, it is a "everything or nothing" logic. Either all the
vertices have a well defined Z value and then you use LINESTRING
Z, POLYGON Z, etc.. Or none of them have, and you use the 2D
versions: LINESTRING, POLYGON, etc.</p>
<p>I believe QGIS has standardized using not-a-number NaN number for
that purpose, but officially, you can't export that to WKT... That
said, for the sake of interoperability with QGIS or other software
using NaN, the OGR WKT importer and exporter also supports its:</p>
<p>$ python -c "from osgeo import ogr; g =
ogr.CreateGeometryFromWkt('POINT Z (1 2 nan)');
print(g.ExportToIsoWkt())"<br>
POINT Z (1 2 nan)<br>
</p>
<p>but I'm not sure if I'd recommend using that convention. I can
imagine exporting NaN to some formats could produce invalid
content.</p>
<p>The good old shapefile uses a similar convention to the -1e300
trick you propose.
<a class="moz-txt-link-freetext" href="https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf">https://www.esri.com/content/dam/esrisites/sitecore-archive/Files/Pdfs/library/whitepapers/pdfs/shapefile.pdf</a>
, page 2 : "Any floating point number smaller than –10^38 is
considered by a shapefile reader to represent a "no data" value"</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 25/01/2024 à 18:07, Abel Pau via
gdal-dev a écrit :<br>
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<p class="MsoNormal"><span lang="EN-US">Hi,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">there is any value in
GDAL for VECTORS that indicates that a concrete value of a Z
is not known (z nodata value)?<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">I couldn’t find it
anywhere.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">In MiraMon format we use
one concrete number documented in our format pdf (</span><span
style="font-size:12.0pt;font-family:"Courier New"">-1.0E+300</span><span
lang="EN-US">) an in the driver it’s planned to translate it
to the same number. I could translate it to the one I am
asking. And the same for detecting nodata Z and translate
them to
</span><span
style="font-size:12.0pt;font-family:"Courier New"">-1.0E+300
</span>
<span lang="EN-US">when reading another format.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks!<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
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