Yeah, I saw that too. Unfortunately the algorithm is only available by
email, and is implemented in Mathematica. It also sounds somewhat
complex.
But I guess this sort of answers my question - there are algorithms
which people have called "concave hull", and they produce concave
polygons from sets of points in some kind of way. I don't think there's
any consensus on what algorithm to use, though.
One interesting approach is here:
http://grass.osgeo.org/wiki/Create_concave_hull
In any case, obviously this isn't in PostGIS right now.
Obe, Regina wrote:
Evidentally its this thing
http://ubicomp.algoritmi.uminho.pt/local/concavehull.html
So I guess basically you take the boundary and you get rid of points
that have points sitting to the right/left/top/or bottom of it and then
you form a polygon from the remaining points.
Well at least that is what it seems like to me visually. Just not
quite sure how to program such a thing without writing yuck procedural
code.
Hope that helps,
Regina
-----Original Message-----
From: [EMAIL PROTECTED] on behalf of
Martin Davis
Sent: Mon 11/24/2008 1:58 PM
To: PostGIS Users Discussion
Subject: Re: [postgis-users] Get concave hull from an array of
longitude inlatitude points
What's a concave hull?
Ales Kecman wrote:
> Hi!
>
>
> I'm new to Postgis and would really like to get some help on getting a
> concave hull from an array of points.
>
> For example:
>
> I have an array of points - longitude and latitude of buildings in
> particular area in the city. I already managed to get a convex hull
> polygon from this array of points, but this is not really helpful.
> What I'm trying to get is some kind of concave hull polygon from an
> array of points, which I would further like to use in Google Earth kml
> file.
>
> Thanks.
> ------------------------------------------------------------------------
>
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> postgis-users@postgis.refractions.net
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>
--
Martin Davis
Senior Technical Architect
Refractions Research, Inc.
(250) 383-3022
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Refractions Research, Inc.
(250) 383-3022
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