On 30/11/16 09:40, Paulo van Breugel wrote:
On Tue, Nov 29, 2016 at 5:44 PM, Moritz Lennert
> An area() function in r.mapcalc would be nice...
Would indeed be a nice addition, but it isn't too difficult to compute,
|export `g.region -g`|
|export `g.proj -j`|
This doesn't work for me as the output is
and +a is not acceptable as variable name.
|r.mapcalc "rcs = (sin(y()+$nsres/2) - sin(y()-$nsres/2)) * ($ewres *
$PI/180) * float($a)^2";|
I tested this approach as well. I.e.
area = above formula
pop_density = pop / area
pop = pop_density * (ewres*nsres)
It is faster than the r.in.xyz approach. But it does not seem to be as
I still lost about 100.000 inhabitants, and more when I smooth more (the
"loss" increases from nearest neighbor to bilinear to bicubic).
In order to avoid precision issues, I tried with both density by m2 and
density by km2, but results are similar.
I don't know which part of the error comes from the use of spheroid
approximation and which part comes from the resampling at reprojection.
But I do think that if it is important to maintain exact totals, then
the r.to.vect - v.proj - v.out.ascii - r.in.xyz solution seems to be
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