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I am trying to loop the r.sun function within a Python script.

Anyway, I seem not to understand how I can stack the raster maps each loop would produce into a single multi-band raster (preferably in geotiff format).

I think one way would be using the list produced with g.list or (even better) g.mlist as input parameter for the i.group function and then export the created group as multi-band file (as shown in the example here). Here is my simple code, modified from this page.

# import the needed modules
from osgeo import gdal
import numpy as np
import grass.script as grass

# prepare the needed input
dem = "dem4comparison@globrad_test"
doy = np.arange(1,366) # day of the year

# calculate slope and aspect maps
grass.run_command("r.slope.aspect",
              elevation = dem,
              slope = "dem.slope@globrad_test",
              aspect = "dem.aspect@globrad_test")

# i is the day of year (DOY) to use for running r.sun
for d in doy:
    # want to get global radiation
    radname = "globrad" + str(d)
    # run the solar model
    grass.run_command("r.sun", flags = "s",
              elevin = dem,
              aspin = "dem.aspect@globrad_test",
              slopein = "dem.slope@globrad_test",
              insol_time = insolname, glob_rad = radname, day = d, step = 1)
    # export the outputs to GTiff files
    grass.run_command("r.out.gdal", input = radname + "@globrad_test", output = radname)

The last row would export each map to a geotiff file after each loop. Rather, I would stack them all into the same multi-band file with n*m*p dimensions, where m and n are rows and columns of my images (each of the same size of course) and p the number of output maps after the loops (that is, 365, the number of the days in a year).

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Only a small modification is needed:

You need to generate the group prior to exporting (i.e., use i.group), then export to a multilayer file by assigning the group name as input in the r.out.gdal call.

  • fine thanks, but how do I go if I want to print a list of my maps created after the loop to be used inside i.group? As I said, I would like to do something like using the output from g.mlist as input for i.group. I red something about standard input and output, but I don't know if that's the way to follow. – umbe1987 Nov 3 '14 at 9:05

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