<div dir="ltr"><div dir="ltr"><div dir="ltr"><div>Updated list with area calculations for</div><div><a href="https://gist.github.com/kbevers/207b5bcb9be20e7554abe5f56742ec2c" rel="noreferrer" target="_blank">https://gist.github.com/kbevers/207b5bcb9be20e7554abe5f56742ec2c</a></div><div><span style="font-family:monospace,monospace"><br></span></div><div><span style="font-family:monospace,monospace">PROJ [1]: 14,737.935 km^2<br>Caris LOTS: 14,737 km^2<br>ArcMap: 14,727.446 km^2<br>MapInfo: 14,727.352 km^2<br>GeoMedia: 14,726.443 km^2<br>Planimeter: 14,722.522 km^2<br>GRASS GIS: 14.718.098 km^2<br><br>EU LAEA [2]: 14,718.098 km^2<br>UTM 33 N: 14,707.742 km^2<br><br>QGIS 3.2: 14,652.181 km^2<br>QGIS 2.8: 14,652.181 km^2 <br><br>[1] geodesic.h:geod_polygonarea()<br>[2] EPSG:3035<br></span></div></div><span style="font-family:monospace,monospace"></span><div><br></div><div>In this case, GRASS GIS provides the best match of geodesic area to metric area.</div><div><br></div><div>@Kristian: are the metric area measurements in "EU LAEA" and "UTM 33 N" suitable as reference?</div><div><br></div><div>Discussion started on</div><div><a href="http://osgeo-org.1560.x6.nabble.com/Re-Qgis-user-New-Features-in-Shape-Tools-3-2-0-td5378898.html">http://osgeo-org.1560.x6.nabble.com/Re-Qgis-user-New-Features-in-Shape-Tools-3-2-0-td5378898.html</a><br></div><div><br></div><div>Markus M</div><div><br></div><div><br></div><div class="gmail_quote"><div dir="ltr">On Mon, Oct 1, 2018 at 2:56 PM Markus Metz <<a href="mailto:markus.metz.giswork@gmail.com">markus.metz.giswork@gmail.com</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"><div dir="ltr"><div dir="ltr"><div dir="ltr"><br><br>On Tue, Sep 25, 2018 at 7:38 PM Helmut Kudrnovsky <<a href="mailto:hellik@web.de" target="_blank">hellik@web.de</a>> wrote:<br>><br>> fyi see<br>> <a href="https://lists.osgeo.org/pipermail/qgis-developer/2018-September/054644.html" target="_blank">https://lists.osgeo.org/pipermail/qgis-developer/2018-September/054644.html</a><br>><br>> with GRASS mentioned<br>> ------------------<br>> Kristian Evers:<br>><br>> Right, here are the calculated areas as returned by a number of different<br>> GIS applications and the planimeter app of GeographicLib for reference:<br>><br>> Caris LOTS: 14.737 km^2<br>> ArcMap: 14.727,446 km^2<br>> MapInfo: 14.727,352 km^2<br>> GeoMedia: 14.726,443 km^2<br>> Planimeter: 14.722,522 km^2<br>> QGIS 3.2: 14.652,181 km^2<br>> QGIS 2.8: 14.652,181 km^2<br><div><br></div><div><div>adding to the confusion:</div><div><br></div><div>I used the geographiclib API as included in PROJ 5.2.0 following the example for geod_polygonarea() in geodesic.h and get</div><div>geographiclib: 14,737.935 km^2<br></div><div>quite different from</div><div>Planimeter: 14,722.522 km^2</div><div><br></div><div>GRASS native gives 14,718.097679</div><div>as also reported by Helmut and Stefan</div><div><br></div><div>Markus M<br></div></div><div>></div>> The polygon that I have used to get the numbers above can be found here:<br>> <a href="https://gist.github.com/kbevers/207b5bcb9be20e7554abe5f56742ec2c" target="_blank">https://gist.github.com/kbevers/207b5bcb9be20e7554abe5f56742ec2c</a><br>><br>> I am quite confident that GeographicLib delivers the most accurate result<br>> (if you have doubts, this reference [0] should convince you). As can be seen<br>> from the table above all but QGIS come fairly close. I expect some variation<br>> in the results as these are numerical approximations, although I think QGIS<br>> is too far of the mark. My suspicion is that the geodesic algorithm used by<br>> QGIS (and apparently GRASS) is to blame here.<br>><br>> /Kristian<br>><br>> [0] <a href="https://arxiv.org/pdf/1102.1215.pdf" target="_blank">https://arxiv.org/pdf/1102.1215.pdf</a><br>> -----------------<br>><br>><br>><br>><br>><br>> -----<br>> best regards<br>> Helmut<br>> --<br>> Sent from: <a href="http://osgeo-org.1560.x6.nabble.com/Grass-Dev-f3991897.html" target="_blank">http://osgeo-org.1560.x6.nabble.com/Grass-Dev-f3991897.html</a><br>> _______________________________________________<br>> grass-dev mailing list<br>> <a href="mailto:grass-dev@lists.osgeo.org" target="_blank">grass-dev@lists.osgeo.org</a><br>> <a href="https://lists.osgeo.org/mailman/listinfo/grass-dev" target="_blank">https://lists.osgeo.org/mailman/listinfo/grass-dev</a></div></div></div>
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