[GRASS-user] Spatial Dissolve

[Darren Cope]

Hi Markus and list,

- I'm using GRASS 6.3.cvs (2006) underQGIS (using the
qgis_setup0.8.1preview3.exe installer from:
http://qgis.org/uploadfiles/testbuilds/) in a Windows 2000
environment.  I've installed qgis in a directory (C:\QGIS) with no
spaces or path names over 8 characters
- the data I downloaded is from the geographynetwork.ca website, and
comes in shapefile format
- Created a new mapset in GRASS (using QGIS GUI)
- Added shapefile to QGIS project
- import shapefile to GRASS vector using v.in.ogr using QGIS "GRASS Tools"
- run v.clean as per CORINE example (v.clean input=wateroriginal
output=waterclean tool=rmdupl) in GRASS shell
- at this point I noticed that the attribute values are not carried
through and I'm left with only "id" and "cat" - why is this, and will
it cause problems later on?
- run v.dissolve (v.dissolve input=waterclean output=waterdissolve) in
GRASS shell, result is a non-dissolved file - I didn't specify a
category, but I'm only doing a "spatial" dissolve, so is this
necessary?
- I also tried v.extract -d (v.extract -d input=waterclean
output=waterextract) in the GRASS shell without success

Hopefully I'm missing something obvious!  Any help would be appreciated.

Cheers,

Darren

On 5/28/07, Markus Neteler <neteler at itc.it> wrote:
> Darren,
>
> could you be more specific about what you did (commands + flags/params),
> which GRASS version etc? I just used this method recently again with
> success.
> The v.patch step in the CORINE example is necessary for *CORINE* since
> you get vector tiles. If you have already a patched map, don't use it.
>
> Markus
>
> Darren Cope wrote on 05/28/2007 02:01 PM:
> > Hi Markus,
> >
> > I must be missing something, because this still does not seem to work.
> > I found another (non-GRASS) way to accomplish this, so the priority
> > is not very high, but I'd still like to figure out the GRASS method.
> > Is the v.patch step in the CORINE example necessary, or mostly just
> > the v.clean step with rmdupl?
> >
> > Cheers,
> >
> > Darren
> >
> > On 5/16/07, Markus Neteler <neteler at itc.it> wrote:
> >>
> >> Hi Darren,
> >>
> >> I also stumbled over this problem, but we solved it. The trick is that
> >> you first have to remove the duplicated tile boundaries, then dissolve
> >> works.
> >> See example for CORINE Landcover SHAPE files:
> >>  http://grass.itc.it/grass63/manuals/html63_user/v.dissolve.html
> >>
> >> Cheers
> >> Markus
> >>
> >>
> >> Darren Cope wrote:
> >> >
> >> > Hi all,
> >> >
> >> > I'm new to GRASS, and using it in Windows via QGIS.
> >> >
> >> > I am attempting to do a "spatial dissolve" (i.e. not dissolve on an
> >> > attribute, but rather just remove unnecessary tile boundaries) on a
> >> > file that I've imported to GRASS from a shapefile, and am so far
> >> > unsuccessful.  The file contains waterbodies, and some of them are cut
> >> > in pieces by tile boundaries.  I would like to remove these
> >> > boundaries.  Can someone please help me out?  I've tried combinations
> >> > of v.extract -d with no success, and am not sure how the "category"
> >> > value apply when I'm not dissolving on an attribute.
> >> >
> >> > So far my search of the archives has turned up something close, but
> >> > nothing that seems to fit my situation exactly.
> >> >
> >> > Cheers,
> >> >
> >> > Darren Cope
> >> > darrencope at gmail.com
> >> > http://dmcope.freeshell.org
>
>
> ------------------
> ITC -> dall'1 marzo 2007 Fondazione Bruno Kessler
> ITC -> since 1 March 2007 Fondazione Bruno Kessler
> ------------------
>
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-- 
Darren Cope
darrencope at gmail.com
http://dmcope.freeshell.org