[GRASS-user] breaking out ("rescuing"?) islands

[David Norris]

Hi,

The short story: Is there a way to "rescue" islands from vector areas? 
In other words, "break" the area up? This is hard for me to put into 
words, so I've drawn a picture to help explain what I want to do:

    <https://netfiles.uiuc.edu/danorris/www/rescue-islands.png>

The long story: I know it isn't topologically correct to do this. The 
problem is that I'm exporting this data as a shapefile for use in 
another program -- and that program doesn't understand "rings" in 
shapefiles! It sees all rings as outer rings, and doesn't understand 
holes. The only way to make this program see the existence of the hole 
would be to break up the polygon as in the diagram above so that it can 
be represented with one simple outer ring. I don't need the data to be 
modeled this way inside GRASS, just in the exported shapefile (or any 
other format that I could then translate into a shapefile).

Aside: I know the proper solution would of course be to add outer/inner 
ring support to this external program, but unfortunately that's not an 
option. It's a kludge, but it's the only way I can think of to get valid 
data into this program!

Many thanks,
-- 
David Norris
danorris at ncsa.uiuc.edu