:Re: [GRASS-user] Some problem about the grass

GRASS GRASS user
,
1

Thank you very for your reply!

In fact I mean the “Categories”, and what you said is very helpful for my understanding something about the grass though not much.

I think what I am now confusing about the grass is how it describe a map either a raster or a vector (actually the raster is my primacy), in other words what can we get from a raster or a vector map? I had read the manual you mentioned “Raster data processing in GRASS GIS”, it says "The geographic boundaries of the raster map are described by the north, south, east, and west fields”, but how?? Is there a example?

I often encounter the following two questions when I use the garss:

  1. The “r.out.gdal”. When I try to convert a map to a geotiff, however the image I got is often a black blank!

  2. Some command which can run normally in the garss can not in the cmd in windows with the tips:

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

C:\Documents and Settings\Administrator>r.shaded.relief map=elevation.dem@PERMANENT shadedmap=ttsh altitude=30 azimuth=270 zmult=1 scale=1 --overwrite

‘“”’ neither a internal or outer command nor a executable program or batch file

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

I have configured the environment variables, and some other commands can run normally such as r.buffe r.info……

PS:

I have just register the maillists of the grass and how can I directly ask or reply in the web pages as in a forum?

Thanks!

Apachemaven
2

apachemaven:

Thank you very for your reply!
In fact I mean the "Categories", and what you said is very helpful for
my understanding something about the grass though not much.

I think what I am now confusing about the grass is how it describe a
map either a raster or a vector (actually the raster is my primacy),
in other words what can we get from a raster or a vector map?

Maybe all this is known to you, but I am writing it anyway.

These are generic questions. You might want to read about data models in
general (basically raster and vector data). A nice and practical view,
through GRASS, about all this is the GRASS book [*]. You will get an
answer as well about what categories are with respect to raster maps.

You can think rasters as matrices and vectors as points, lines or closed
polygons. Depending on the nature of what you want to represent in a
map, you either choose raster (like for temperature of precipitation
maps) or vector (location of weather stations, roads or burned areas).

Of course there are data that can be represented in both raster and
vector maps. It's always a question of what you have and what you want
to achieve.

I had read the manual you mentioned "Raster data processing in GRASS
GIS", it says "The geographic boundaries of the raster map are
described by the north, south, east, and west fields”, but how?? Is
there a example?

Absolutely. I (can) set the geographic boundaries for Peloponnese, South
Greece for example like that:

g.region s=36 e=23.6 n=38.5 w=21

Note that the above values are geographic (=degrees) and NOT projected
coordinates. We can do something similar in a projected coordinate
system with values given in metres.

You know that there are many GRASS-related tutorials [1]. And even more,
GFOSS related [2] ?

1) The “r.out.gdal”. When I try to convert a map to a geotiff,
however the image I got is often a black blank!

That one might NOT be a problem if you just have not set your "region"
correctly.

It can be a problem sometimes related with color table rendering. You
could try to remove the color table (r.colors -r YourMap) before
exporting.

There are some tips in the manual about this [3]. And there is a long
discussion in GRASS-trac [4]

2)

Sorry but I have no working experience with GRASS under Operating
Systems (or environments) other than Linux.

PS:

I have just register the maillists of the grass and how can I directly
ask or reply in the web pages as in a forum?

You can register your self in GRASS' wiki [5] and add/edit almost
anything. The wiki is from and for the community.

Cheers, Nikos
---

[*] http://www.grassbook.org/

[1] http://grass.osgeo.org/gdp/tutorials.php

[2] http://wiki.osgeo.org/wiki/Educational_Content_Inventory

[3] http://grass.itc.it/grass64/manuals/html64_user/r.out.gdal.html

[4] http://trac.osgeo.org/grass/ticket/73

[5] http://grass.osgeo.org/wiki/Main_Page

3

On Wed, 2009-03-18 at 18:51 +0100, Nikos Alexandris wrote:

(like for temperature of precipitation

maps)

a small but perhaps an important typo:
...like for temperature OR precipitation
maps...