[GRASS-user] identify features without cat [solved]

[Dylan Beaudette]

On Monday 08 October 2007, Hamish wrote:
> Dylan Beaudette wrote:
> > After some frustration with the GRASS-R functionality as implemented
> > via temp shapefiles, I realized that the source of the problem was
> > features missing cat values.
>
> I've just added a note about this to vectorintro.html as it is
> an unobvious feature of GRASS vector processing.

Great. It turned out that the problems I was experiencing were related to 2 
things: 
1. broken topology 
2. areas without a centroid. 

manual edits with v.digit fixed the first problem and v.category type=area 
option=add fixed the second. 

Just goes to show that garbage in = garbage out. 

> > I poked around with v.edit, but did not see any simple way to ID or
> > remove features missing a cat value. The '-c' option in v.out.ogr was
> > a temporary fix, but I would like to be able to identify / remove
> > cat-less features without using v.out.ogr .
> >
> > Any tips on how to do this / or where work would need to be done?
>
> to add category numbers use v.category or v.centroids.
>
> you might give all newly categorized features a cat number of 99999
> (cat=99999 step=0) then extract those to another map with v.extract
> and compare.
>

It might be a good idea in the manual to define the behavior of v.category, 
when the input has features with and without centroids, and when the 
option=add... It seems like it ignores all existing centroids, and adds to 
areas which were previously missing them ?

Thanks!

Dylan


-- 
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341