Markus Metz wrote:
On Sun, Apr 1, 2012 at 11:45 PM, David J. Bakeman<[email protected]> wrote:
David J. Bakeman wrote:
Markus Neteler wrote:
On Sun, Apr 1, 2012 at 9:45 PM, David J. Bakeman<[email protected]>
wrote:
I didn't find an answer in the archives so.
I have a shapefile of polygons and some of the polygons are duplicated.
I
thought I could use v.clean tool=rmdupl to get rid of these polygons. I
use
v.in.ogr to read it in and I get the following:
WARNING: 8 areas represent more (overlapping) features, because polygons
overlap in input layer(s). Such areas are linked to more than 1
row in attribute table. The number of features for those areas
is
stored as category in layer 2
That is correct in that there are 8 duplicate polygons but the only
different attribute is the cat which grass added? What am I missing? I
then tried v.clean tool=bpol,rmdupl and nothing changes it still has the
8
duplicates. What am I doing wrong?
I think that you need to add the break tool for v.clean.
Correct that was actually what I was using: v.clean tool=break,rmdupl
Looking closer I see that when I run v.clean it doesn't even report the
duplicates that v.in.ogr did but they are still there. The only thing that
differs in coordinates or attributes is the cat attribute that grass added.
I am using grass 6.3.0 on fedora core 14 linux.
Please note that you can upgrade to grass-6.4.0-4.fc14:
http://koji.fedoraproject.org/koji/buildinfo?buildID=263115
Thanks I'll see if I can upgrade.
I upgraded to the 6.4.0 and the results are exactly the same. The polygons
really are identical in every respect except for they have different values
in the cat column. Is there some other grass tool for removing this kind of
duplicate?
After import with v.in.ogr, there are no duplicate geometries left in
the vector. What you have now is some areas with two categories
assigned to them. Removing the duplicates means in this case removing
one of the two categories, for example with one of the vector
digitizers.
I'm relatively new to grass but that doesn't make sense. I started with
a shapefile with duplicate features. That is polygons with the exact
same attributes and geometry (they are identical). What I thought grass
could do for me was to read it in and delete one of the duplicates
without user intervention. After all it identifies the duplicates so
why can't it delete one?
Are you saying that the duplicate geometry was deleted but it kept both
rows even though they were identical as well? Is there a operation that
would identify and delete rows that differ in only the cat attribute.
Markus M
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