I imported a landcover shapefile in grass and I'm interested in only
one of the land cover class. So after importing with v.in.ogr and
running v.clean with bpol, I extracted only the class I'm interested
and now I want to get some statistics for each class polygon.
The problem is that this shapefile is one of those "multipart" files,
that is, only one line in the attribute column for many polygons. That
is, all polygons have category = 5. To make things worse, there are
islands...
So, to calculate the stats for each polygon I though about removing
the categories and adding them back again, to later use v.to.db but,
then the island will get categories too.
On Mon, 2009-01-26 at 16:40 -0200, Daniel Victoria wrote:
Hi all,
I imported a landcover shapefile in grass and I'm interested in only
one of the land cover class. So after importing with v.in.ogr and
running v.clean with bpol, I extracted only the class I'm interested
and now I want to get some statistics for each class polygon.
The problem is that this shapefile is one of those "multipart" files,
that is, only one line in the attribute column for many polygons. That
is, all polygons have category = 5. To make things worse, there are
islands...
So, to calculate the stats for each polygon I though about removing
the categories and adding them back again, to later use v.to.db but,
then the island will get categories too.
So, any hints as to how should I go about it?
Thanks
Daniel
Hi Daniel.
Isn't it possible to assign new cats to specific features?
v.category in=A out=A.del option=del type=boundaries # or type=line
v.category in=A.del out=B option=add type=boundaries # or type=line
Well, here is where I get lost. Because of the islands. The polygons
of interest all have category=5 and the island have no cats. If I
delete the cats and add them again, the islands will get categories.
I just tough of this: Maybe create a new column and copy the old
categories there. Then delete and add all categories again and
calculate the statistics. After that, all I need to do is look for the
old_cat column to find the area of each polygon that is NOT AN ISLAND.
Does that sound reasonable? Any better (smarter) way of doing this? I
really need to understand this vector/database business better....
Cheers and thanks
Daniel
On Mon, Jan 26, 2009 at 5:02 PM, Nikos Alexandris
<nikos.alexandris@felis.uni-freiburg.de> wrote:
On Mon, 2009-01-26 at 16:40 -0200, Daniel Victoria wrote:
Hi all,
I imported a landcover shapefile in grass and I'm interested in only
one of the land cover class. So after importing with v.in.ogr and
running v.clean with bpol, I extracted only the class I'm interested
and now I want to get some statistics for each class polygon.
The problem is that this shapefile is one of those "multipart" files,
that is, only one line in the attribute column for many polygons. That
is, all polygons have category = 5. To make things worse, there are
islands...
So, to calculate the stats for each polygon I though about removing
the categories and adding them back again, to later use v.to.db but,
then the island will get categories too.
So, any hints as to how should I go about it?
Thanks
Daniel
Hi Daniel.
Isn't it possible to assign new cats to specific features?
v.category in=A out=A.del option=del type=boundaries # or type=line
v.category in=A.del out=B option=add type=boundaries # or type=line
Well, here is where I get lost. Because of the islands. The
polygons of interest all have category=5 and the island have no
cats. If I delete the cats and add them again, the islands will get
categories.
v.overlay saved the day!! It did take some time to run but the output
was right what I wanted, even with the database fields in the original
vector map!
once again, thanks
Daniel
On Mon, Jan 26, 2009 at 6:35 PM, Hamish <hamish_b@yahoo.com> wrote:
Daniel Victoria wrote:
Well, here is where I get lost. Because of the islands. The
polygons of interest all have category=5 and the island have no
cats. If I delete the cats and add them again, the islands will get
categories.