[GRASSLIST:5070] Getting started with GRASS

[Michael Ash]

This is the reply of an amateur user, and I happily defer to
anyone with real expertise.  It took me a long time to
understand how to get anything out of GRASS, but now I am a
dedicated user.

I strongly recommend beginning with one of the tutorials
listed at http://grass.ibiblio.org/gdp/index.html Most of
them come with sample datasets to use, e.g., leics
(Leicestershire, GB) or spearfish (South Dakota, USA). I
learned a lot from the Leicestershire tutorial
http://www.geog.le.ac.uk/assist/grass/seeds/gs_html.html

I also recommend the book Open Source GRASS: A GRASS GIS
Approach by Neteler and Mitasova.

> I have pass the first wall. I need some Grass help. what
> is the meaning of Location, mapset and database.

The database gives the path of the directory that contains
the complete collection of GRASS datasets that you use.

The Location is defined by the core information about the
particular area that you are examining (region, coordinate
system, projection, datum).  Note that "create a new
location" is an option on the opening GRASS screen, and the
prompts, e.g., "choose a projection," are pretty clear for
creating a new location.  (It took me a long time to notice
the new location option, and I could only create new maps by
importing them to existing locations and rearranging.)

The mapset is a particular collection of maps (layers) for
the location.  A Location often has two mapsets: PERMANENT
(which contains the basic maps given for the Location as
well as the basic location, projection, datum info) and
<username> (which contains maps that you have created by
analyzing, recoding, calculating, etc. from the PERMANENT
mapset).  You only need one mapset per Location if you do
not mind using and changing the PERMANENT collection.

Each mapset then contains a collection of vector, raster,
and site maps.  A map is a collection of files that includes
the GIS data, categories, attributes, labels, etc.

> I sort get that they are related to the actual path
> where the data is? Am i correct? I have made the
> following dir structure Inside Home i have created Mapa
> dir, and inside it a vector dir and inside it a rio dir
>
> /home
> /home/mapa
> /home/mapa/vector
> /home/mapa/vector/rio
>
> inside rio i have make two files:
>  head (with nothing in it)
>
> and frmt with
> FORMAT:postgis
> HOST:192.168.0.1
> PORT:5432
> DATABASE:ejercicio
> USER:postgres
> PASSWORD:xxxx
> GEOM_TABLE:rios
> CAT_TABLE:rios
> #GEOM_ID:
> #GEOM_TYPE:
> #GEOM_GEOM:
> #CAT_ID:
> #CAT_FIELD:
> #CAT_CAT:
>
> rios is a NTAM table in ejercicio. I am using it again
> for categories. Is that all right or i have to separate
> geometry from categories in pgsql/gis?

I don't know what this means.

> after running grass51 i have set
>
> location:   vector
> Mapset:     rio
> database: /home/mapa/
> <esc><enter>
>
> welcome to grass 5.1
> bla bla bla
> GRASS:/home/map/vector/rio> d.mon start=x0
> d.mon: error while loading shared libraries: libpd.so: cannot open shared object file: No such file or directory.
>
> GRASS:/home/map/vector/rio>

> where do i have the mistake?

(0) You may have a problem with the GRASS installation.
The shared libraries error does not sound good.

(1) I don't think that you have a valid location.  I really
recommend downloading some of the tutorial datasets and
exploring the organization of files.

> Do I need that pqsql library installed in the client
> machine? why? Is is already installed on the pgsql
> server.

I don't know.  I don't think that you need any sql material
for basic map processing, only if you want to connect
database information to your maps.  You can get a lot done
without a database connection.  (But I would be grateful for
a simple tutorial.)

> Do i need to make this path structure by hand for each
> layer i want to use in grass eventhough they are all
> stored in the same pgsql/GIS database?

I don't know.



-- 
Michael Ash, Assistant Professor
  of Economics and Public Policy
Department of Economics and CPPA
University of Massachusetts
Amherst, MA 01003
Tel 413-545-6329 Fax 413-545-2921
Email mash at econs.umass.edu
http://www-unix.oit.umass.edu/~maash