[GRASSLIST:9601] Re: v.buffer - creating buffer areas does not work

[Hamish]

> this bug's URL: http://intevation.de/rt/webrt?serial_num=3910
> ---------------------------------------------------------------------
> 
> Subject: v.buffer - creating buffer areas does not work
..
> GRASS Version: 6.1.cvs
..
> I tried to create a new area boundary around a line theme (where the
> lines describe a closed ring). Thought it would be easy to do it like
> this:
> 
> v.buffer in=ausschnitt out=buff_ausschnitt bufcol=gesamtbr
> type=boundary
> 
> But GRASS won't create a new theme (there is result theme
> "buff_ausschnitt", but it is not possible to open it: QGIS "The layer
> is no valid layer and cannot be added to the map").

If there are no boundary features in the input map, the buffering around
boundaries will be empty. Use v.type to convert.

Remember that lines will be buffered both sides, areas (boundaries) only
outside themseleves.


> bufcol=

I don't guarantee that option is free of bugs yet. Actually I can 
guarantee it has bugs, and is currently only ok for points. 
Need to add a temporary warning I guess. Search for the thread on 
the devel list for more info. 

Currently a combo of multiple 'v.extract where=' + v.buffer, then
v.overlay will probably do to get your job done.


> After that, I tried to first create a line buffer theme (works fine)
> and then convert it to a area boundary theme using v.type. However,
> the new area boundary theme does not have the shape of the line buffer
> theme. The new created polygon fills out the space inside the ring.

d.vect cat=1-999999

will draw only real features (not fill holes).


I think you need to run v.type before v.buffer.



Hamish