[GRASS5] Q. How do you find the islands for a given area?

Eric G. Miller egm2 at jps.net
Sat Feb 24 20:52:21 EST 2001

On Sat, Feb 24, 2001 at 03:32:20PM -0800, Rich Shepard wrote:
> On Sat, 24 Feb 2001, Eric G. Miller wrote:
> > I've been looking into the d.area island drawing problem.  Anyway, I'm
> > trying to figure out how you find out:
> >
> >   For a given area A:
> >     How many interior boundary islands does it have?
> >     How do I get line_pnts struct(s) for just these interior islands?
> Eric,
>   Funny that you mention this. In order to better help David with the
> v.in.mif (and v.in.shape) modules, I've discovered the subject I need to
> learn: computational geometry. My buddy in Boulder (CO) pointed me to Joseph
> O'Rourke's book, "Computational Geometry in C", 2nd Edition; I bought a copy
> last night at Powell's Technical Books in Portland. This book contains the
> answer to these questions and a bunch of other vector-related questions.

Yea, I've heard of this O'Rourke book.  Been meaning to pick it up.
There are a couple of others I've seen mentioned in many places.

Anyway, the question was more directed at the GRASS interface functions,
then for algorithms.  Turns out my test vector layer wasn't getting
built right.  After much futzing with v.digit and v.support, I finally
managed to build one that had the properties I was looking for.  So, now
I have to see if I can get d.area filling only areas that have been
labelled while "cutting out" the areas of internal islands... Basically
have to turn multiple polygons into one for the polygon fill operation.

Eric G. Miller <egm2 at jps.net>

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