[GRASS-dev] problem using pygrass

[Javier Martínez-López]

Dear Pietro,

thank you very much for your help! I will upgrade the GRASS version
and try again, and will close the maps before changing the region, if
possible. I am using CentOS linux. This is a great tool!

Cheers,

Javier

On Thu, Feb 27, 2014 at 10:06 PM, Pietro <peter.zamb at gmail.com> wrote:
> Hi Javier,
>
> On Thu, Feb 27, 2014 at 4:45 PM, Javier Martínez-López
> <javi.martinez.lopez at gmail.com> wrote:
>> I have a couple of problems when using pygrass for analyzing raster
>> maps stored in GRASS with the numpy library:
>
> The RasterNumpy class was quite buggy, I did some changes last week
> that should fix some of them, which version are you using?
>
>> - First: I cannot close the maps, since I always get the following error:
>>
>>>>> import numpy
>>>>> import grass.pygrass as pygrass
>>>>> demx = pygrass.raster.RasterNumpy('dem')
>>>>> demx.open('r')
>>>>> dem2 = demx.flatten()
>>>>> len(dem2)
>> 43860
>>>>> demx.close()
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>>   File "/usr/local/grass-7.0.y14/grass-7.0.svn/etc/python/grass/pygrass/raster/__init__.py",
>> line 654, in close
>>     self._write()
>>   File "/usr/local/grass-7.0.y14/grass-7.0.svn/etc/python/grass/pygrass/raster/__init__.py",
>> line 597, in _write
>>     self.tofile(self.filename)
>> ValueError: 43860 requested and 0 written
>
> yes, this bug should be fixed in (r59127), I've tried this code using
> the North Carolina mapset:
>
> from grass.pygrass.raster import RasterNumpy
> elev = RasterNumpy('elevation')
> elev.open()
> flt = elev.flatten()
> len(flt)
> elev.close()
>
> and it works, are you in Linux?
>
>> - Second: when I change the region (with g.region) and read again some
>> maps, it uses the same extent as before and I always get a "core dump
>> error". I print the region in the script and it has in deed changed
>> but I always get maps from the same size as before...
>
> in numpy the raster map is read and load into the memory when you open
> the map using the current region, so changing the region when your map
> is opened will not affect the raster map. Using the other RasterClass
> will easily raise some errors.
> So it is not a worth idea change a region when one or more raster maps
> are opened, the right way to go is: set the region, do something with
> the raster map, close then you are free to change the region again.
>
> I would like to introduce the with statement also for the Region
> object, to do something like:
>
> {{{
> ## change resolution
> with Region(nsres=100., ewres=100.) as reg:
>     # do something with the changed region
>     #
>
> ## back to the original region
> #
> }}}