[GRASS-user] many polys / 1 cat

[Daniel Victoria]

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 at 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
>
> Regards, Nikos
>
>