[GRASS-user] exporting areas to shapefiles without filling holes

[Markus Metz]

Markus Neteler wrote:
> On Thu, Apr 9, 2009 at 10:38 AM, Hamish <hamish_b at yahoo.com> wrote:
>   
>>
>> Markus Metz:
>>     
>>> Maybe use v.out.ogr -c?
>>>       
>> yup, that's it. I'd focused on the shapefile example in the man page
>> and totally missed the blinking red letters at the top:
>>     
>
> I am also regularly missing that (and only now understand how to
> solve this island problem).
>
> Any chance to generate a warning if islands are there and -c not
> given? Only then the problem + solution is obvious...
>   
Hmm, what is the most common desired situation? Exporting features also 
if they don't have a category or only exporting features with a category?

In the case of areas I guess that areas without centroids (typically 
(parts of) islands) should most commonly appear as holes and not as 
filled areas. I assume that points and lines usually have categories, so 
the -c flag should generally not make a difference. Boundaries usually 
don't have categories (although they can), and exporting boundaries as 
lines is a special case.

My question is if the behaviour of v.out.ogr could be changed for grass7 
to export only features with categories by default if this is the most 
common situation, e.g. invert the meaning of the -c flag.