[GRASS-dev] area calculations in several GIS

[Helmut Kudrnovsky]

fyi see 
https://lists.osgeo.org/pipermail/qgis-developer/2018-September/054644.html

with GRASS mentioned
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Kristian Evers:

Right, here are the calculated areas as returned by a number of different
GIS applications and the planimeter app of GeographicLib for reference:

Caris LOTS: 14.737 km^2
ArcMap:     14.727,446 km^2
MapInfo:    14.727,352 km^2
GeoMedia:   14.726,443 km^2
Planimeter: 14.722,522 km^2
QGIS 3.2:   14.652,181 km^2
QGIS 2.8:   14.652,181 km^2

The polygon that I have used to get the numbers above can be found here:
https://gist.github.com/kbevers/207b5bcb9be20e7554abe5f56742ec2c

I am quite confident that GeographicLib delivers the most accurate result
(if you have doubts, this reference [0] should convince you). As can be seen
from the table above all but QGIS come fairly close. I expect some variation
in the results as these are numerical approximations, although I think QGIS
is too far of the mark. My suspicion is that the geodesic algorithm used by
QGIS (and apparently GRASS) is to blame here.

/Kristian

[0] https://arxiv.org/pdf/1102.1215.pdf 
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best regards
Helmut
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