[GRASS-user] grass topography and postgis

[Matt B]

Hi Markus,
I possibly don't have a full understanding of what topology is. I thought it
was more or less the geometry, with a few rules relating different objects
to each other. Attributes are things like place names or a value at a
location, within a boundary etc. As postgis allows the storage of geometries
then isn't this the topology? I've not had much luck with grass getting it
to recognise things like shared boundaries (so I only have to digitise them
once) apart from using the snap to vertice feature (though as postgis seems
the most useful at the moment I'm concentrating on that).

Thanks
Matt



On Tue, Dec 2, 2008 at 7:45 PM, Markus Neteler <neteler at osgeo.org> wrote:

> Matt,
>
> On Tue, Dec 2, 2008 at 4:31 AM, Matt B <mattslists at gmail.com> wrote:
> > Hi Group,
> > I'd like to set up grass to edit / work with data in a postgis database.
> So
> > far I've figured out (and been informed, thanks Richard) that grass
> stores
> > the topologoly data in it's own database and the external database is
> just
> > used for attributes.
>
> GRASS stores per default all data (geometry + attributes) in its own format
> (i.e., attributes in a DBF file in GRASS 6 and in SQLite in GRASS 7).
>
> Optionally attributes can be stored in PostgreSQL (not PostGIS), Mysql,
> SQLite, and ODBC.
>
> > Is there a way to have grass store the topology data in
> > postgis so I can easily work with the data in different applications?
>
> Yes, using v.external. But note that this is a read-only connection.
> We hope that in future this will be read-write.
>
> The issue behind this is that GRASS is a topological GIS while
> PostGIS is Simple Features (no topology per default). So there
> is a "conversion" needed between these two worlds.
>
> Markus
>
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