[GRASS-user] attempt to define a smaller region

Helmut Kudrnovsky hellik at web.de
Mon Dec 14 05:46:49 PST 2015

jamaas wrote
> I'm a beginner with GRASS, running newest version 7.0.2 on Ubuntu Linux
> 14.04.
> I'm attempting to create a new smaller region, and change the resolution
> to something slightly larger.  For some reason the map I get in the GUI
> display window is very detailed however when I try to set a new region
> using g.region it tells me that there is no detail to do it.
> Apologies for all of the detail.  
> - This is working with raster maps from the UK ordinance survey (OS)
> system
> - Originally downloaded four individual raster maps from OS is a sort of
> .asc format
> - Then converted them to ARCGIS format using ARCGIS
> - Then combined them into one raster using mosiac to raster, then
> converted back to .asc
> - I've now imported the .asc raster into GRASS and it looks fine, lots of
> detail but I want try to do some hydrologic modelling using TOPMODEL so
> need to produce and topidx file, but before that I want to get a smaller
> region
> -when I attempt to get a smaller region using g.region I get an invalid
> input error.
> -when I look at the raster info using g.region -p, there is almost no
> information
> ==========================
> (Mon Dec 14 11:36:09 2015)                                                      
> g.region -p                                                                     
> projection: 99 (Transverse Mercator)
> zone:       0
> datum:      osgb36
> ellipsoid:  airy
> north:      1
> south:      0
> west:       0
> east:       1
> nsres:      1
> ewres:      1
> rows:       1
> cols:       1
> cells:      1
> (Mon Dec 14 11:36:09 2015) Command finished (0 sec)                
> ===============================
> Something doesn't add up, the information must be in the raster because I
> can see it, any suggestions as to what I've done wrong or how to extract
> the correct region using UK british national grid references?
> Thanks for any suggestions pointing me in the right direction.

adjust the region to your raster, e.g.

g.region -a raster=elevation at PERMANENT align=elevation at PERMANENT
g.repion -p to show the region settings

then digitize a vector polygon for the region of your intereset, then do

g.region -a raster=elevation at PERMANENT vector=yourvector
align=elevation at PERMANENT

to shrink your region to the area of your interest

g.repion -p to show the region settings


best regards
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