[GRASS-user] Obtaining unique nodes from a topology

[William Temperley]

2010/1/15 Hamish <hamish_b at yahoo.com>

> Will wrote:
> > Thanks - but what I really want is a list of unique nodes
> > (i.e. where three boundaries meet, there would be one node,
> > with an id) and assign this id to the relevant boundaries.
> > Perhaps that isn't possible. It might be easier to do
> > this in PostGIS.  I need to be able to run recursive
> > queries in PostGIS to pick up connected boundaries.
>
> Hi,
>
> have a look at 'v.build option=dump,sdump,cdump'.
>
> there you can export the topology to stdout, etc.
>
>
> it would be nice if you could write up your findings/method
> into a small wiki page when you are done, there is a real lack
> of PostGIS+GRASS documentation.
>
>
> Hamish
>
> Hi Hamish

Where should I write such a wiki page do you think? To be honest I'm not
sure I'm using best practices - I needed a quick fix for a one-off job -
I've been using shapefiles as an interchange medium.

I just rolled my own start/endpoint thing - it was pretty simple in Postgis
to run
/* get table of unique start/endpoints */
insert into node (geom)
select st_startpoint(geom) from bound
union
select st_endpoint(geom) from bound

then
/* assign node ids to bounds */
update bound set startnode_id = (select id from node where node.geom =
st_startnode(bound.geom))

Cheers

Will
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