[GRASSLIST:2535] Re: [GRASS5] [5.7] remove islands and U-dangles?

[Radim Blazek]

On Monday 09 February 2004 16:37, Hamish wrote:
> > > I've got a vector area which contains a bunch of islands and
> > > polygons attached to the inside edge of the outer polygon. What
> > > commands would one use to remove and 'flatten' the overlapping
> > > areas?
> > >
> > >
> > > eg
> > >
> > >
> > > /-------+---+----------\
> > >
> > > |       | X |          |
> > > |       | X |  <- area |
> > > |       |---|          |
> > > |  |
> > > |  |=| <- island       |
> > >
> > > \----------------------/
> > >
> > >
> > > In the end I want a convex hull of the outer polygon as a single
> > > entity, without losing resolution from a points->v.hull step.
> >
> > Sorry, I don't quite understand what you need, could you send me any
> > more intuitive images/description?
>
> my ascii art is poor..
>
> see attached PNGs. (1 is from d.vect, 2 & 3 are from v.digit)
>
> I have a vector file with an island as a big polygon, it has both the
> coastline + river boundaries. The river polygons share a common boundary
> with the coastline where they meet the ocean. Inland the river polygons
> break off into topologic "islands", maybe because of a lake or a marsh
> breaks the river.
>
> I want a vector of only the outside coastline, with the rivers and
> topo-islands removed.
>
> By using v.extract I can get rid of the inner topo-islands by copying
> out only the outer big islands' category number.
>
> But I still can't get rid of the connected river polygons.

If I understand well, v.extract type=area new=1 list=1-10000 (categories of all areas)
with -d (Dissolve common boundaries) flag shoud do that, unfortunately
-d flag is disabled because there is a bug in the code which removes centroids.

Radim