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

[Micha Silver]

Markus Metz wrote:

>
> 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.
So what would then happen if you export a vector which includes closed 
boundaries which have no cat, and centroids with the cat value? (and you 
request type=area)??
 --
Micha