[GRASS-user] How to extract multiple raster values to points

GRASS GRASS user
1

Hello,
I wonder if there is a way to extract/sample (eg using nearest neighbour) the values from multiple rasters that correspond to a set of to vector points into a table.
I could find a way to do this for one raster, but not for multiple rasters. Has anyone done this in GRASS?
Thank you,
Raphael.

2

Hi,

On Fri, Mar 23, 2012 at 5:06 PM, Raphael.Viscarra-Rossel@csiro.au wrote:

Hello,
I wonder if there is a way to extract/sample (eg using nearest neighbour) the values from multiple rasters that correspond to a set of to vector points into a table.
I could find a way to do this for one raster, but not for multiple rasters. Has anyone done this in GRASS?

Not sure if i got what you mean to do. With r.what you can extract the characteristics from multiple rasters, given the coordinates of the points you are interested in. If you have multiple points, you can apply r.what iteratively using a simple script, i.e.:

#! /usr/bin/python

import os, sys
from glob import glob
import grass.script as grass

topidx = sys.argv[1]
accMFD = sys.argv[2]

fpath = ‘your/path/to/coordinates/file’

coordinates is a txt file in which coordinates are stored

coord = open( os.path.join(fpath, ‘coordinates’), ‘r’).readlines()
pairs =

for line in coord:
line = line.strip()
x, y = line.split(‘\t’)
pairs.append( x + “,” + y )

r_what = grass.read_command(‘r.what’, input = ‘topidx,accMFD’, east_north = pairs)

create a new file output

fout = open( os.path.join(fpath, ‘output’), ‘w’)
fout.write(r_what)
fout.close()

Hope this helps,
madi

–
Ing. Margherita Di Leo, Ph.D.

3

Hello,
I would suggest to use v.what.rast with multiple runs - one for each
of the raster maps. It's more simple than passing around coordinate
pairs.
Or if other sampling strategies are required (i.e. with bilinear
interpolation), the v.sample is the right tool.

Maris.

http://grass.osgeo.org/grass64/manuals/html64_user/v.what.rast.html
http://grass.osgeo.org/grass64/manuals/html64_user/v.sample.html

2012. gada 23. marts 18:39 Margherita Di Leo <diregola@gmail.com> rakstīja:

Hi,

On Fri, Mar 23, 2012 at 5:06 PM, <Raphael.Viscarra-Rossel@csiro.au> wrote:

Hello,
I wonder if there is a way to extract/sample (eg using nearest neighbour)
the values from multiple rasters that correspond to a set of to vector
points into a table.
I could find a way to do this for one raster, but not for multiple
rasters. Has anyone done this in GRASS?

Not sure if i got what you mean to do. With r.what you can extract the
characteristics from multiple rasters, given the coordinates of the points
you are interested in. If you have multiple points, you can apply r.what
iteratively using a simple script, i.e.:

#! /usr/bin/python

import os, sys
from glob import glob
import grass.script as grass

topidx = sys.argv[1]
accMFD = sys.argv[2]

fpath = 'your/path/to/coordinates/file'

# coordinates is a txt file in which coordinates are stored
coord = open( os.path.join(fpath, 'coordinates'), 'r').readlines()
pairs =

for line in coord:
line = line.strip()
x, y = line.split('\t')
pairs.append( x + "," + y )

r_what = grass.read_command('r.what', input = 'topidx,accMFD', east_north =
pairs)

# create a new file output
fout = open( os.path.join(fpath, 'output'), 'w')
fout.write(r_what)
fout.close()

Hope this helps,
madi

--
Ing. Margherita Di Leo, Ph.D.

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