[GRASS-user] new user question about mapsets, locations, and coordinate systems

[Nikos Alexandris]

Hi!

On Sun, 2008-12-07 at 15:08 -0800, mtnbiketrail at zzz.com wrote:
> I'm using 6.3 on Ubuntu with QGIS.
> If I create a new location, under PERMANENT,

The PERMANENT mapset is created automatically for each new LOCATION.
However, you cannot create a (new) LOCATION *under* the PERMANENT
mapset.

(Something like... LOCATION > Mapset(s) )

>  does that coordinate system 
> that I specify for PERMANENT the default coord sys for a new mapset I 
> create under that location?

Yes. Each new mapset within a pre-defined LOCATION (of some coordinate
reference system) will obtain the (same) defined cooridante reference
system.

> I have different raster and vector maps I 
> want to use and they are all different coord systems. Can I have a 
> different coord system for each mapset?

I don't think so. You need to create as many LOCATIONS as your different
coordinate reference systems in which your geodata are
"projected/defined".


> For the DATABASE parameter, is GRASS smart enough to add on the LOCATION 
> directory.


Yes, by default grass uses the dbf under
"$GISDBASE/$LOCATION_NAME/$MAPSET/dbf/" [1]. I always change it (to use
sqlite) and don't really "remember" if the creation of a new mapset will
create a new "bdf" directory in it. But it should :-)
 
Anyhow, you need to use db.connect in order to define which DBMS you
want to use and where you want to store the database.

>  IS the DATABASE always the same, even if I create different 
> LOCATIONS?


I think not. It's not *correct* (?) to use the same database (of some
location) directly from another location.

I had some trouble when I did that once (I was experimenting): I messed
up let's say "original" data stored in the PERMANENT with edited data on
another mapset/ another location by using the same name.

Perhaps somebody with more experience can give his valuable view upon
the subject.

> So should I create the PERMANENT coord system with what I want to use( 
> which is wgs84 UTM).

You probably need a LOCATION defined by the WGS84 (epsg=4326) geographic
coordinate system. In the PERMANENT mapset (within your newly created
LOCATION) will be imported all data initially. Then, it is a good
practice (but not a MUST) you probably would like to create another,
user-mapset (your own mapset), copy over the data (from the PERMANENT to
YourMapset) and start playin with your data.


>  So I can use QGIS and its "on the fly" option.

Don't understand here/ Don't know the answer.
> 
> I tried to do this with the text based interface, but kept getting weird 
> stuff, like ESC+ENTER didn't always work.

Which operating system do you work with?

Regards, Nikos
[1] http://grass.osgeo.org/grass64/manuals/html64_user/db.connect.html