[GRASS-user] Removing inner lines in merged vector map

[Markus Metz]

On Wed, Jun 22, 2011 at 7:32 PM, puffbunnyn <arne.kaldhusdal at gmail.com> wrote:
> Hello
>
> I have merged three CORINE vector maps for coniferous, broad-leaved and
> mixed forests in order to create one general map for all forests as I need
> to calculate the length of the forest edges.
>
> After using v.patch (with flag e) to merge the maps I have tried my best to
> remove all lines lying inside of boundaries so that only the outer
> boundaries would be left - with no luck. The main problem should be that the
> adjacent boundaries from the three maps have only been put next to another
> and not really "merged" (this is not a problem concerning double
> boundaries). Does anyone know how to cope with this? I have not been able to
> find any posts regarding this problem and would really appreciate your help.
>
When patching areas, a bit of cleaning is needed before anything else
can be done.

Try

v.clean tool=bpol,rmdupl

if there are any incorrect boundaries or duplicate centroids left, try

v.clean tool=break,rmdupl,rmsa

repeat this until tool=rmsa makes no modifications

If you want to remove the inner boundaries, you could prepare the
vector for v.dissolve with

v.category op=del cat=-1

followed by

v.category op=add cat=1 step=0 type=centroid

Now all areas have the same category and you can use v.dissolve or
v.extract -d to remove the inner boundaries.

Markus M