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I have been using the IDW interpolation tool through GRASS plugin in QGIS and the interpolation output I am getting is for the entire mapset region.

My question is: Is there a possibiltity that we can interpolate a certain small region within a given MAPSET region and not the entire MAPSET region ?

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If you use GRASS in QGIS Processing framework the mapset is not used.

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  • ok. So are you suggesting that there is a way I can interpolate through GRASS tools without using a mapset. If so, will you tell me how to do it? Feb 27 '14 at 4:13
  • If your using QGIS 2+ press 'ctrl + alt + m'. Type interpolation and pick one of the methods. Or use the menu Processing > Toolbox.
    – Jakob
    Feb 27 '14 at 7:37
  • ok this was nice idea that you told me. Thanks Also do you know how to do this through GRASS shell and add it to the display window.? The Grass IDW interpolation i did through the command line gives an output file different than this one and i also don't know how to add that to display window. Your method is different than mine and is way easier, i just need you to help do it through grass shell command line. Feb 27 '14 at 8:24
  • I have no experience with the GRASS shell. For a more low level run of GRASS methods I use Processing from the QGIS Python console or script like: processing.runalg('grass:r.los',"Elevation",'642229,5598076',None,75,5000,False,'700000.0,710000.0,6200000.0,6220000.0',None,'C:\\r_LOS')
    – Jakob
    Feb 27 '14 at 10:00
  • Thanks Jakob, your suggestion of using 'CTRL + ALT + M' was great and gave me the desired output. Also I wanted to tell you that I figured out how to do it through the command line, which I will mention as an answer to this question below Mar 4 '14 at 4:24
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The Interpolation through GRASS plugin tools can be done through an alternative method as Jakob mentioned using the 'CTRL + ALT + M', which gives the IDW interpolation for the smaller region where the points exist and not for the entire mapset. Thanks to JAKOB.

Also, the way to do it through command line (i.e. GRASS Shell) is that when we use 'CTRL + ALT + M' -> Go to v.surf.idw interpolation -> IDW Interpolation Dialog Box.

In the 'IDW Interpolation Dialog Box' give all the inputs and parameters and when you Run the tool, try to

"quickly copy the commands under the LOG tab in the same IDW dialog box"

When you read this log file you will notice that it is basically the same thing which will happen if you use the GRASS shell and run the same 3-4 commands from a '.sh' file using "sh TestCommand.sh" command in GRASS command line.

So just read the LOG file and pick the exact commands to be copied to a '.sh' file -> Copy the exact commands to your '.sh' file and just run it through GRASS shell using "sh abcCommand.sh" command (assuming that 'abcCommand.sh' is your '.sh' file that you created in this case)

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