[QGIS-Developer] QGIS gives different area calculation result compared to PROJ

[Andrea Giudiceandrea]

dr wrote
> So I would say it seems like an error in the area calculation algorithm in
> QGIS.

Hi,
there is no unique way to calculate the geodesic area.

For example, PROJ use a C implementation of the GeographicLib algorithm,
while QGIS uses the same algorithm used by GRASS, SpatiaLite 5 uses RTTOPO
library and PostGIS uses GeographicLib.

See this recent threed
http://osgeo-org.1560.x6.nabble.com/Confusion-with-ellipsoidal-method-of-area-td5454013.html
on the same topic.
There are two feature requests for QGIS and GRASS:
https://github.com/qgis/QGIS/issues/40888
https://github.com/OSGeo/grass/issues/1235
and a Pull Request in GRASS https://github.com/OSGeo/grass/pull/1283.

So it look like there is the possibility that GRASS will switch to use the
same C implementation of the GeographicLib algorithm used by PROJ.

Regards.

Andrea



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