On Thu, May 18, 2017 at 4:22 PM, James Duffy <james.philip.du...@gmail.com> wrote: > > 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.
This is a large difference. Is it possible that several polygons share the same category? In this case the entry in the attribute table is the sum of all polygons with that category. > > I am working in WGS84. GRASS uses geodesic distance and area calculation for latlon, I believe QGIS as well. Markus M > > 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
_______________________________________________ grass-user mailing list grass-user@lists.osgeo.org https://lists.osgeo.org/mailman/listinfo/grass-user