extract data from several images to different shapefile columns using GRASS

Question

I am now working in grass and I want to extract raster values from several images to a shapefile. I have already created the columns in the .shp where the raster values will be stored but I am facing difficulties on how will I make the loop...

What I want is to extract the values of image_1 to column_a, values of image_2 to column_b etc etc... The problem that I have is that I can't make the loop for two variables (raster image and shapefile column) together... It must be easy but I am new in grass and bash in general as you must have already understood.

The command that I used is "v.what.rast"

Thank you!

Answer 1

You can create a loop to iterate through your data using v.what.rast. If you update your field names with an integer (e.g. column_1, column_2 ..), the following loop should work.

    i=0
    for image in `g.mlist type=rast patt=*image_regexp*`
    do
      v.what.rast vector=target_vector raster=$image column=column_$1
      $((i++))
   done

I'm almost certain that you'll need to import your Shp file into the GRASS native vector format using v.in.ogr, because as far a I know, v.external creates a read-only link to the dataset.