[GRASS-user] Some questions

[Hamish]

Martin Besta wrote:
> >
> >> /I was trying first v.buffer, then v.db.addtable and finaly
> >v.overaly > intersect with input line for buffer. But then is the
> >output line > again.
> >> /
Hamish:
> > can you reproduce the effect using the demo spearfish dataset, and
> > post the command line commands?/
> >  
 
> Buffer 5 meters for layer of roads from sperfish60 dataset
> 1. v.buffer input=roads output=roads_5m type=point,line,area layer=1
>   buffer=2.5 scale=1.0 tolerance=0.01
> 
> 2. v.db.addtable map=roads_5m layer=1 'columns=cat integer, atribut
>   integer' 
>
> 3. v.overlay ainput=roads atype=line alayer=1 binput=roads_5m
>   btype=area blayer=1 output=overlay_roads_buffer5m operator=and
>   olayer=1,0,0 
>
> Output is always a line, however i need the polygon.

The output is correct for "v.overlay operator=and". The intersection
between the two vectors only happens where they both exist, and that is
only exactly on the line.

see
 http://grass.ibiblio.org/grass60/screenshots/vector.php
 http://grass.ibiblio.org/grass57/tutorial/vectoroverlay.html


> When I am executing v.overlay (to clip my map with boundary line) I 
> recieve always the clipped line (ainput is line, binput is area), 
> however I need the polygon. When I switched first and second input 
> layer, I had recieved an empty layer.

I think you want "v.select operator=overlap", not v.overlay.



Hamish