[GRASS-user] Some problem about the grass

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Wed Mar 18 00:54:29 EDT 2009

On Wed, 2009-03-18 at 11:03 +0800, apachemaven at yeah.net wrote:
> I want to know how can I understand the map in the grass?
> for example what is catalogy, type ? Also what is the meanning of the
> "current region" as I had came the problem many times.

Hi apachemaven!

* I 've never heard or read anything about "catalogy" in GRASS.

* Type refers, usually, to a raster data type. For example if the pixel
values of a raster map are integers or floating point. Check the "Raster
Formats" section in "Raster data processing in GRASS" page of the GRASS
manual [1] and you are probably interested about data types [2].

* The _region_ concept (in general) is easy to understand. It is a very
useful concept in GRASS' raster engine.

When you set the "region" in GRASS (e.g. with the module "g.region") you
limit all raster processing operations within this region. For example,
if you have a raster map of Africa and you are interested in doing some
raster processing in Cameroon *only*, then you set your "region" to
match the extent of Cameroon (e.g. using the geographic coordinates if
you work in Long-Lat). Almost all raster modules will then operate over
Cameroon and not to the whole map (the whole of Africa in this example).

Now, there might be some confusion derived from the several terms that
are used: current region, computational region, region of a map, active
region, etc. There actually, I think, only 3 possibilities:

 1. the region _or_ extent of a map ("r.info -g" for a raster map or
"v.info -g" for a vector map), whether this is a 2D or 3D map.

 2. the active _or_ computational region of GRASS' raster engine, again
either 2D or 3D.

 3. in addition, one is able to save a region and recall it later at any
time with "g.region region=YourSavedRegion". Something like a "bookmark"
so you don't need to re-define from the scratch a "region of interest".

To answer directly your question: "current region" is, well, the
currently set region. You can check that with "g.region -p".

Hope this helps.
Kind regards, Nikos

[1] http://grass.osgeo.org/grass64/manuals/html64_user/rasterintro.html


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