[GRASS-user] Spatial Dissolve

[Leonardo Lami]

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 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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