[GRASS5] Re: Vector format proposal

[Radim Blazek]

Andrea Aime wrote:
> Well, I can't say that I fully agree with you, Radim and David,
> because I like a more simple approach, like teachers :-)
> Anyway, freedom of choice is important and your points are
> relevant, althoght in my applications they're not (I'm using
> GRASS as a backend for analysis and let the user view and
> manipulate data thru commercial applications, and I need vector
> capabilities because I would like to perform all calculation on
> server side, now vector overlays are performed client side
> by Autocad Map :-( ...)
> So, if I want to stick to my poor's man data representation
> (the shapefile model) I should follow some convention,
> such as putting only one type
> of data in each vector map and using the following string to
> associate geometry to attributes:
>
> * 1 $MAP id $GISDBASE/$LOCATION/$MAPSET/dbf dbf
>
> If I undestand correctly this means that every map is linked
> to its own db file, that this file is named as the map and the
> link it done thru an integer index. That's good for me.
> If I link data thru an hypotetical PosgreSQL driver
> the thing would look something like:
>
> * 1 $MAPSET_$MAP id geodb_$LOCATION pgsql
>
> so that a map named geology in mapset Andrea in location Modena
> would be stored in the database geodb_Modena, in a table named
> Andrea_geology... will it be possible?

Exactly.

> And what about table creation? It shold be made by hand or there
> are some tools that let you specify the table structure?
> And what happens when I perform a g.remove? There should be an
> option to delete the table along with the data (an option, so that
> I can decide to leave the table in place, too)

There are no modules yet for creating table (db.execute may be used
of course and works with dbf driver) but there is function in dbmi library
so that it could be used instead of constructing create statement in 
modules. 

g.remove should be able delete table. In proposal is option '-t'
for specification if module should/should not  create/delete table also.

There are many opened questions for database connection.

> Let's consider a particular case of overlay: it starts from
> two polygon layers and ends into a new polygon layer representing
> intersection. Each polygon in the result should have attributes
> from both maps (so, it is a spatial join), and I expect the result
> to be linked to a new table that has columns from both of the
> input tables... but what happens if the input data is linked to more
> than one table? Should I cross every table with each other? Don't do
> it at all and have the resulting data linked to each of the input
> tables (sigh, this would be that I would have to do some kind of
> post-processing to return back to the shapefile model...)
> Any idea?
> Regards
> Andrea Aime
>

Radim


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