[GRASS-user] Grass, Python, mapcalc

[Paul Meems]

Thanks again Daniel for your help.

When I do the calculation in the GUI instead of in the Python shell I get
these results:
r.mapcalc sun = global1 at temp+ global2 at temp
(Fri Dec 28 12:26:10 2012) Command finished (1 sec)
r.mapcalc sun = sun at temp+ global3 at temp
ERROR: Unable to close raster map

When I Google on the error message I find this post from 2010
http://lists.osgeo.org/pipermail/grass-user/2010-October/058463.html saying:

>* Why am I obtaining this error? and How can I avoid it?*
Because you're using the same map as both input and output, which
won't work. Either use a temporary name for the intermediate map, or
replace the second grass.mapcalc call with r.null.

I'll have a look in using a temp file. This will make my script more
complicated ;)

Thanks,

Paul

 *Paul Meems *
Release manager, configuration manager
and forum moderator of MapWindow GIS.
www.mapwindow.org

Owner of MapWindow.nl - Support for
Dutch speaking users.
www.mapwindow.nl

*
*


2012/12/28 Daniel Lee <lee at isi-solutions.org>

> Hi there,
>
> I'm now trying to use r.sun and r.mapcalc with Python to create my annual
>> solar radiation map.
>> I'm using the Python shell inside GRASS.
>>
>> For testing purposes I start with 9 days.
>> The r.sun part seems to be working:
>> for x in range(1, 10, 1):
>>     print "Working on day %d" % (x)
>>     glob_rad = 'global' + str(x)
>>     grass.run_command('r.sun', flags = 's', elevin = 'w001001 at temp',
>> aspin = 'aspect at temp', slopein = 'slope at temp', glob_rad = glob_rad, day
>> = x)
>> I do have a question about parsing the --overwrite flag. How to do that.
>> Adding flags='s, --overwrite' or flags='s, -overwrite' gives a compile
>> error.
>>
>
> I believe you overwrite by setting:
> flags="s, o"
>
>
>>
>> Now I try to combine the results of r.sun into 1 raster.
>> This is working:
>> for x in range(1, 10, 1):
>>     if x == 2:
>>       exp = 'sun = global1 at temp + global2 at temp'
>>       print exp
>>       grass.mapcalc(exp, quiet=False, verbose=False, overwrite=True)
>>
>> This is also working:
>> for x in range(1, 10, 1):
>>     if x == 2:
>>       exp = 'sun = global1 at temp + global2 at temp'
>>       print exp
>>       grass.mapcalc(exp, quiet=False, verbose=False, overwrite=True)
>>     elif x > 2:
>>       exp = 'sun = sun at temp + global' + str(x) + '@temp'
>>       print exp
>> and produces this output:
>> sun = sun at temp + global3 at temp
>> sun = sun at temp + global4 at temp
>> sun = sun at temp + global5 at temp
>> sun = sun at temp + global6 at temp
>> sun = sun at temp + global7 at temp
>> sun = sun at temp + global8 at temp
>> sun = sun at temp + global9 at temp
>> But when I execute this using
>> grass.mapcalc(exp, quiet=False, verbose=False, overwrite=True)
>>  Grass crashes completely.
>>
>> Has this something to do with having the output file is the input file as
>> well?
>> If this is not allowed how can I combine all output files from r.sun into
>> 1 raster?
>>
>
> GRASS doesn't care what you're combining, when you use the map calculator
> it just sees numbers so that shouldn't be a problem.
> I don't know why the map calculator to overwrite the input map would be a
> problem either. I'm not familiar with your syntax though. What happens when
> you just enter the expression on the "normal" command line?
>
> r.mapcalc "sun = sun + global3"
>
> That should work.
>
> Best,
> Daniel
>
>
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