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

Justin Hickey jhickey at hpcc.nectec.or.th
Mon Feb 26 02:29:28 EST 2001

Hi Eric

"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:

I'm sorry I didn't read my mail this weekend, but the most efficinet way
to solve your problem is to use a computer graphics algorithm for
filling polygons. This algorithm handles convex polygons, concave
polygons, self-intersecting polygons, and polygons with holes (or
islands in your case). Since you already did a lot of coding, you may
not be interested in this algorithm. However, if you are interested, it
can be found in the book "Computer Graphics: Principles and Practice" by
Foley, Van Dam, Feiner, and Hughes (see section 3.6 "Filling Polygons").
If you cannot find this book, let me know and I'll see what I can do to
summarize the algorithm for you. Note that with this algorithm, you do
not have to worry about which areas are islands. However, you may need
to modify this if you have nested islands.


Jazzman (a.k.a. Justin Hickey)  e-mail: jhickey at hpcc.nectec.or.th
High Performance Computing Center
National Electronics and Computer Technology Center (NECTEC)
Bangkok, Thailand
People who think they know everything are very irritating to those
of us who do.  ---Anonymous

Jazz and Trek Rule!!!

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