They're similar, but I'm not sure they're 100% the same in all cases.
In the "mainland plus islands" case it seems there is a requirement to
ensure that all the input polygons are contained in the result. The
concave hull concept as presented is based purely on a point set, and
thus might not necessarily cover all of the input polygons.
Also, the concave hull is defined by a distance tolerance. In a
situation with islands both very close and very far, it might be hard to
find a distance value which would include all islands but not compromise
the shape of the main polygon too much.
Of course it all depends on the data - there's probably lots of cases
where both would produce similar results.
Tim Bowden wrote:
On Mon, 2008-11-24 at 11:45 -0500, Travis Kirstine wrote:
I don't think that the geom union would in combination with the
boundary would attach the island to the mainland. I don't think that
there is a simple answer to my problem but I have attached a pic to
help illustrate what I'm trying to accomplish.
Regards
Looking at that image seems to me it's just another case of what Regina
pointed to (http://ubicomp.algoritmi.uminho.pt/local/concavehull.html)
in the concave hull thread.
Regards,
Tim
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
