[GRASS-user] Change GRASS region multiple times

[Pietro]

Dear Luna,

On Wed, Mar 2, 2016 at 10:40 PM, Luna, Daniel Eduardo <DEL47 at pitt.edu> wrote:
> I need to create a new raster map during the execution. I'm using the
> commands:
>
>         from grass.pygrass import raster
>
>         newRasterMap = raster.RasterSegment('new')
>         newRasterMap.open('w', 'CELL')
>

Do you really need RasterSegment? Do you need to write raster map not
in a sequential mode?


> I've noticed that new raster maps are created with the resolution of the
> current region in GRASS. I've noticed also that it is possible to change the
> current region during the execution of my new module using the script
> 'g.region'. However, it looks like if I want to change the resolution again,
> the script 'g.region' does not have any effect. My conclusion: GRASS can
> change the current region just 1 time during the execution of a module. Is
> that correct?

No, the region affect only the current process, using the g.region
module you are using an external process that should not have effect
on your process.

> I would like to know how can I develop a new module (using pygrass) where I
> could be able to create three new raster maps with different resolutions
> each?

I wrote some code for testing
You can create a module that do your analysis, and then you can call
your module setting different regions (see function
test_different_regions1),
otherwise you can work only in the same process (see function
test_different_regions3).
I've also define a function (test_different_regions2) that mix ctypes
and external process, but If it is uncomment the
test_different_regions3 is not working any more... and I'm not able to
understand why... :-)

{{{
from grass.pygrass.modules import Module
from grass.pygrass.raster import RasterSegment
from grass.pygrass.gis.region import Region


def test_different_regions1(rinput, routput, method, *resamples):
    """Function using only external process, through GRASS modules"""
    for res in resamples:
        Module('g.region', raster=rinput, res=res, flags='ap')
        Module('r.resamp.stats', input=rinput,
               output=routput+'_{res}'.format(res=res),
               method=method, overwrite=True)


def write_raster(rinput, routput):
    """Function that work with input/output raster maps"""
    with RasterSegment(rinput, mode='r') as rin,
RasterSegment(routput, mode='w', mtype=rin.mtype, overwrite=True) as
rot:
        for irow, row in enumerate(rin):
            rot.put_row(irow, row * 2)
        print(rot.info.nsres, rot.info.ewres)


def test_different_regions2(rinput, routput, *resolutions):
    """Mixing external processes (g.region) with current"""
    for res in resolutions:
        Module('g.region', raster=rinput, res=res, flags='ap')
        write_raster(rinput, routput + '{res}'.format(res=res))
    #Module('g.region', raster=rinput, flags='a')


def test_different_regions3(rinput, routput, *resolutions):
    """Working only with current process"""
    reg = Region()
    for res in resolutions:
        reg.nsres, reg.ewres = res, res
        reg.write()
        reg.set_raster_region()
        print(reg)
        write_raster(rinput, routput + '{res}'.format(res=res))

print("\n\nOnly GRASS modules", "\n" + "=" * 30)
test_different_regions1('elevation', 'tmptest', 'average', 50, 100, 200)

# Uncomment to change behaviour of test_different_regions3
#print("\n\nGRASS modules and ctypes", "\n" + "=" * 30)
#test_different_regions2('elevation', 'tmptest', 50, 100, 200)

print("\n\nOnly ctypes", "\n" + "=" * 30)
test_different_regions3('elevation', 'tmptest', 50, 100, 200)
Module('g.remove', type='raster', pattern='tmptest' + '*', flags='f')

}}}

Happy coding

Pietro