[GRASS-user] v.select - so close but so far!

[M S]

i not doing anything advanced, at least it shouldnt be.   i have a county
wide, line roads dataset and county wide building points dataset.  all i
want to do is clip both vectors back to the same extent. basically i just
want the features either clipped to the boundary of a polygon i built, or
even just select overlapping ones, and write them to a new file.

i may be missing the concept of this, "features need a category number in
order to be extracted. does d.what.vect show cat numbers for your points?"

d.what.vect shows catagory numbers for the building points.  I'm not sure i
understand what the category has to do with v.select.

v.info clipper does show boundaries and centroids and area (and
islands?!?)   i recently modified the clipper polygon box, and it seems that
the centroid is outside the box now.  i'll put it in and give it another
whirl.

thanks for the help!

On 6/22/06, Hamish <hamish_nospam at yahoo.com> wrote:
>
> > i'm using v.select as such:
> >
> > v.select ainput=buildings atype=point alayer=1 binput=clipper
> > btype=area blayer=1 outpout=buildclip operator=overlap
> >
> > where buildings are a point, with layer 1 (verified through QGIS)
> > where clipper is a polygon that is the bounds i want to pull the
> > building points from.  the odd thing about this dataset, is that when
> > i go to load in QGIS, there are two layer options, layer 0 which is
> > polygon and layer 1 which is line.
> >
> > i cant specify blayer=0 in this function or it says must be 1 or
> > greater.
> >
> > is there a way to put the polygon layer on layer 1? i can only think
> > this might be why there's a problem.  I still dont really grasp the
> > layers concept very well.  i understand it has to do with linking
> > features to a database, but why does it put different features on
> > different layers?
> >
> > the output i get is a file with no data in it.
>
>
> I don't think QGIS layers == GRASS layers.
>
> Unless you are doing something advanced, usually grass vector layer is 1
> and you can forget about that.
>
> "v.info clipper"  show boundaries + centroids or lines?
>
> features need a category number in order to be extracted. does
> d.what.vect show cat numbers for your points?
>
> v.select works well and should be pretty simple, so don't give up.
>
>
> Hamish
>
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