<div dir="ltr">Thanks for your prompt and detailed reply!</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Feb 19, 2021 at 5:32 PM Andrea Giudiceandrea <<a href="mailto:andreaerdna@libero.it">andreaerdna@libero.it</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">dr wrote<br>
> So I would say it seems like an error in the area calculation algorithm in<br>
> QGIS.<br>
<br>
Hi,<br>
there is no unique way to calculate the geodesic area.<br>
<br>
For example, PROJ use a C implementation of the GeographicLib algorithm,<br>
while QGIS uses the same algorithm used by GRASS, SpatiaLite 5 uses RTTOPO<br>
library and PostGIS uses GeographicLib.<br>
<br>
See this recent threed<br>
<a href="http://osgeo-org.1560.x6.nabble.com/Confusion-with-ellipsoidal-method-of-area-td5454013.html" rel="noreferrer" target="_blank">http://osgeo-org.1560.x6.nabble.com/Confusion-with-ellipsoidal-method-of-area-td5454013.html</a><br>
on the same topic.<br>
There are two feature requests for QGIS and GRASS:<br>
<a href="https://github.com/qgis/QGIS/issues/40888" rel="noreferrer" target="_blank">https://github.com/qgis/QGIS/issues/40888</a><br>
<a href="https://github.com/OSGeo/grass/issues/1235" rel="noreferrer" target="_blank">https://github.com/OSGeo/grass/issues/1235</a><br>
and a Pull Request in GRASS <a href="https://github.com/OSGeo/grass/pull/1283" rel="noreferrer" target="_blank">https://github.com/OSGeo/grass/pull/1283</a>.<br>
<br>
So it look like there is the possibility that GRASS will switch to use the<br>
same C implementation of the GeographicLib algorithm used by PROJ.<br>
<br>
Regards.<br>
<br>
Andrea<br>
<br>
<br>
<br>
--<br>
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</blockquote></div>