On Thu, May 18, 2017 at 4:22 PM, James Duffy <james.philip.du...@gmail.com>
> I'm trying to calculate the area of a polygon using v.to.db as follows
> execGRASS("v.to.db", flags = c("p","quiet"), parameters = list(map =
"test", units = "meters", option = "area", separator = "comma"),intern =
> 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.
> Can anyone shed some light on how v.to.db calculates area and why it
might be going wrong please?
> Thank you
> James Duffy
> PhD Researcher
> Environment and Sustainability Institute
> Penryn Campus
> University of Exeter
> TR10 9FE
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