[GRASS-user] Grass, Python, mapcalc

Paul Meems bontepaarden at gmail.com
Fri Dec 28 05:08:51 PST 2012

Thanks Sotiris,

I've tried your suggestion but converted it to Python because I'm on
This is my script:
grass.run_command('g.mremove', rast = ('out*'))
grass.mapcalc('sun=global1', quiet=False, verbose=False, overwrite=True)
for x in range(2, 10, 1):
  exp = 'out=sun+global' + str(x)
  print exp
  grass.mapcalc(exp, quiet=False, verbose=False, overwrite=True)
  grass.run_command('g.rename', flag='o', rast = ('out','sun'))

This doesn't result in the expected outcome.
sun is equal to global1 and no values are added
out is global1+global2 but is no more values are added. But mapcalc is
called several times.
I've tested this with:
r.what --v -f -n input=global1 east_north=156287.225281,383024.737026
r.what --v -f -n input=sun east_north=156287.225281,383024.737026
r.what --v -f -n input=out east_north=156287.225281,383024.737026

Not only am I a new user to GRASS but I'm also still a novice in Python.
Most likely it is something in my script.

If somebody has a different approach to get the solar radiation of a whole
year I'm happy to try that.



Date: Fri, 28 Dec 2012 14:36:15 +0200
> From: "S. Koukoulas (lists)" <sotkouklistes at gmail.com>
> To: grass-user at lists.osgeo.org
> Subject: Re: [GRASS-user] Grass, Python, mapcalc
> Message-ID: <50DD923F.806 at gmail.com>
> Content-Type: text/plain; charset=windows-1252
> To my experience with r.mapcalc you cannot do what yo do with
> programming languages... e.g. i=i+1 will not work directly. Instead you
> could try a more indirect way, something like (here is an example with
> bash shell script):
> #g.mremove rast=out* (to remove previous stuff, if needed)
> r.mapcalc sun=global1
> for a in ?seq 2 10?; do
> r.mapcalc out = sun + global$a
> g.rename --o rast=out,sun
> done
> basically the main idea is to use an intermediate map and then before
> the loop ends, pass it (with g.rename) to the map variable you want.
> There might be a more elegant way with python, but hopefully this shell
> script example might help you.
> HTH,
> sotiris
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