On Tue, Sep 25, 2018 at 7:38 PM Helmut Kudrnovsky <hel...@web.de> wrote: > > fyi see > https://lists.osgeo.org/pipermail/qgis-developer/2018-September/054644.html > > with GRASS mentioned > ------------------ > 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
adding to the confusion: I used the geographiclib API as included in PROJ 5.2.0 following the example for geod_polygonarea() in geodesic.h and get geographiclib: 14,737.935 km^2 quite different from Planimeter: 14,722.522 km^2 GRASS native gives 14,718.097679 as also reported by Helmut and Stefan Markus M > > 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 > ----------------- > > > > > > ----- > best regards > Helmut > -- > Sent from: http://osgeo-org.1560.x6.nabble.com/Grass-Dev-f3991897.html > _______________________________________________ > grass-dev mailing list > grass-dev@lists.osgeo.org > https://lists.osgeo.org/mailman/listinfo/grass-dev
_______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-dev