Hi James, QGIS uses a ellipsoidal area measurement, while GRASS (like most of the other GIS) uses a Cartesian measurement (others, please correct me if that is not the case in WGS84).
See amongst others: https://issues.qgis.org/issues/12057 and https://issues.qgis.org/issues/14675 Would you mind comparing area measurement of a third software (SAGA, PostGIS, ...)? Cheers Stefan ________________________________________ Von: grass-user [grass-user-boun...@lists.osgeo.org] im Auftrag von James Duffy [james.philip.du...@gmail.com] Gesendet: Donnerstag, 18. Mai 2017 16:22 An: grass-user Betreff: [GRASS-user] v.to.db area calculations Hello, I'm trying to calculate the area of a polygon using v.to.db as follows (through R): execGRASS("v.to.db", flags = c("p","quiet"), parameters = list(map = "test", units = "meters", option = "area", separator = "comma"),intern = TRUE) I assume that the output of this command will be a meters squared calculation of the area inside the polygon 'test'. However, in QGIS, I manually calculated the area the they do not match. QGIS (which I believe to be true) shows 0.128m2, and the output from v.to.db shows 22.42226m2. I am working in WGS84. Can anyone shed some light on how v.to.db calculates area and why it might be going wrong please? Thank you James -- James Duffy PhD Researcher Environment and Sustainability Institute Penryn Campus University of Exeter Penryn Cornwall TR10 9FE _______________________________________________ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user
