[GRASS-user] v.extract -d vs. v.dissolve

Nikos Alexandris nikos.alexandris at felis.uni-freiburg.de
Mon Nov 10 15:30:13 EST 2008


On Mon, 2008-11-10 at 12:09 +0100, Nikos Alexandris wrote:
> On Sun, 2008-11-09 at 23:57 -0800, Hamish wrote:
> > Nikos:
> > > What could be the reason for v.dissolve failing to dissolve when
> > > v.extract -d works just fine with the exact same vector maps? Bug?
> > 
> > [map sent]
> > 
> > what do you mean by "failing"? topology results seem the same before and
> > after, ie there were no borders which needed to dissolve.  (v.info -t)

Hamish,

I think I misunderstood the function of v.dissolve here :-(

1. My map seems to be already "dissolved", that is: there are no
adjacent polygons carrying the same "value"

2. When I dissolve the already "dissolved" map based on the "values"
column, the module reclassifies and brings the "unique" "values" in a
cat column (right?)

3. With db.select I see only 4 different categories. That's right. I
though that I now have only 4 BIG areas (something like the multipart
shapefile concept). This is where I got confused - My bad... !

I guess it's ok to use my already dissolved map or just add a column and
populate unique id's for each of the polygons.

Sorry for the un-necessary time-crunching.

Regards, Nikos



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