[R] alpha shape function

roger koenker rkoenker at uiuc.edu
Wed Feb 18 14:46:07 CET 2009

As it happens, I have also been looking into this.  I began by  
Ken Clarkson's hull:  http://www.netlib.org/voronoi/hull.html  but  
discovered that its alpha shapes don't seem to treat holes in regions,  
simply connected regions.  (I would be happy to hear to the contrary, if
someone has other experience.)  There is a nice matlab implementation
http://www.mathworks.com/matlabcentral/fileexchange/6760 which I've
also experimented with using R.matlab, but  this is still very early  
The matlab version is only 2d, whereas Clarkson does "moderate d"    
extends at least to 3d.
Given tripack, it seems like alpha-shapes shouldn't be such a big  
enterprise, and
might  make a nice project for someone with an interest in computational
geometry.   Hint, hint.  Nudge, Nudge.

url:    www.econ.uiuc.edu/~roger            Roger Koenker
email    rkoenker at uiuc.edu            Department of Economics
vox:     217-333-4558                University of Illinois
fax:       217-244-6678                Champaign, IL 61820

On Feb 18, 2009, at 7:20 AM, Pedroso MOACIR wrote:

> Hi all,
> I want to approximate te shape of an area defined by a set of points.
> The convex hull is not good enough, but I think that an alpha shape
> would be fine. I did an RSiteSearch(),  google search, RSeek.org  
> search,
> looked at the CRAN Views, but was unable do find a function in R that
> computes the alpha shape.  Does anyone know if there is such a  
> function
> in R?
> Theank you very much.
> Moacir Pedroso
> Embrapa - Brazil
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