[GRASS-user] TO BE POST: Extract a smaller image (sample) from a raster map

[Nikos Alexandris]

Liria Boix wrote:
> Hi everyone:

Hello Liria,

> Have Modis images MOD13Q1 reprojected into Tiff format imported
> into grass to analize NDVI for different months and seasons. As I just
> need to analize NDVI for a specific crop area of the image imported, I want
> to extract or select that region from the raster map.

You need to use g.region to set the "computational region", that is the extent 
to which (almost) all grass raster modules will operate on.

> After reading several post explaining that R.region/G.region
> should be use to set the geographic boundaries,

The "r.region" module will define/modify the boundaries of the image itself, 
not the extent where the raster operations will take place.  This module is 
useful, for example, in case the extent or the "placement" of a raster map is 
not the one it should be/the user wants it to be.

> I decided to follow the
> instruction and have use r.region setting nort, south, east and
> west values of the smaller area BUT only get the same image narrower in
> width and longer in high.

You need to use g.region.

> Now, when I follow the use of this command again I get the message "unable
> to parse command r.region"
> 
> I'm new in Grass! and feel confuse. What I am missing? Please help! Many
> Thanks in adavance.

Please have a quick-read through the following useful material:

- <http://grass.osgeo.org/grass64/manuals/rasterintro.html>
- <http://grass.osgeo.org/grass64/manuals/imageryintro.html>

There are several references upon "r.region" and "g.region".

Best, Nikos