[GRASS-user] Re: [GRASSLIST:1175] add centroids automatically to area boundaries

[Ulrich Leopold]

On Thu, August 10, 2006 15:48, Moritz Lennert wrote:
> On Thu, August 10, 2006 15:33, Ulrich Leopold wrote:
>>>> I have a patched vector map with lines. These lines should be converted
>>>> into area boundaries in order to receive areas. Once boundaries are
>>>> retrieved I still need  to attach centroids to them in order to overlay
>>>> with *another* vector map which already consists of boundaries and
>>>> areas
>>>> including centroids. How can I achieve this?
>>>>
>>>> I tried to convert all lines into boundaries with
>>>> v.type type=line,boundary
>>>>
>>>> It seems to work as there are only boundaries left. Next step would be
>>>> to add automatically centroids to these boundaries. How can this be
>>>> done?
>>>
>>> Hi,
>>>
>>> see v.category for this. I have added a micro FAQ for this:
>>> http://grass.gdf-hannover.de/wiki/Convert_vector_types
>>
>> I tried that already but it did not work. It even changes the polygons
>> back to
>> single lines. But good that you opened a micro FAQ to add the solution
>> later.
>> Any other ideas?
>
> Are you sure your lines are closed, thus defining real areas ? You can
> check with v.digit.

I put a screenshot on the WiKi page:
http://grass.gdf-hannover.de/wiki/Convert_vector_types

The lines seem to be closed. But a lot of boundaries are without areas as you
can see from the legend on the right hand side.

And v.clean does not do the job. I used v.type to convert from lines to
boundaries.

So possibly that the problem are boundaries with no areas? But then how can I
change that?