[GRASS-user] Spatial Dissolve

[Markus Neteler]

On Tue, May 29, 2007 at 05:23:42PM +0200, Leonardo Lami wrote:
> Darren Cope ha scritto:
> > 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?
> See the output message of v.in.ogr, maybe there is some problems in the
> structure of the input table
> > - 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 see this bug with v.dissolve that is present only in grass 6.3

I don't think that it is a bug. If there are duplicated boundaries,
v.dissolve must fail.

(see also my other mail how to solve this)

Markus

> > - I also tried v.extract -d (v.extract -d input=waterclean
> > output=waterextract) in the GRASS shell without success
> Here you must specify the category list that you want extract or a query
> 
> Ciao
> leonardo
> >
> > 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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> >>
> >
> >
> 
> 
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