[R] Finding a 3D convex hull in R

[Liaw, Andy]

Prof. Ripley,

Have you looked at the qhull software at www.geom.umn.edu/software/qhull (as
I write this note, that link is not working for me.  I could, however, get
to http://www.cs.sunysb.edu/~algorith/implement/qhull/distrib/)?  The paper
that described the algorithm is
http://www.acm.org/pubs/toc/Abstracts/toms/235821.html.

I've thought about interfacing R to it (but have not actually tried).  If
it's not worth trying, I won't.

Regards,
Andy

> -----Original Message-----
> From: Prof Brian D Ripley [mailto:ripley at stats.ox.ac.uk]
> Sent: Saturday, September 22, 2001 2:53 AM
> To: Greg Jefferis
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] Finding a 3D convex hull in R
> 
> 
> On Fri, 21 Sep 2001, Greg Jefferis wrote:
> 
> > Dear List Members,
> >
> > I'm presently carrying out morphological analysis of a data 
> set of neuronal
> > structures.  These are essentially 3D binary trees.  In due 
> course I will be
> > trying to use discriminant analysis or other methods to 
> classify these
> > neurons based on morphological variables such as total tree 
> length, segment
> > number etc.
> >
> > I would like to calculate a 3D convex hull for a set of 
> X,Y,Z data points
> > which define the tips of my neurons.  I have found the R 
> function chull
> > which finds a 2D convex hull, but not have found any 3D routines.  I
> > wondered if there were any packages / publicly available 
> code I could use.
> > Having found the convex hull, it would be handy if there 
> were also functions
> > to find the centroid, volume etc.  I've only been using R 
> for 10 days and am
> > not much of a programmer, so I would rather not have to 
> write code to
> > interface to external C routines etc if possible.
> 
> 3D convex hull programs are very much more specialized than 2D ones.
> When I added chull I looked at the possibility of allowing kD, k > 2,
> but it was hard to find suitable code, let alone interface to it.
> Known algorithms are far too complicated to implement 
> tolerably at R level.
> 
> netlib.bell-labs.com/netlib/voronoi/hull.html
> 
> is one place I considered starting, but note the portability comments.
> 
> 
> > Very many thanks for any suggestions,
> >
> > Greg.
> >
> > P.S. I'm running R 1.3.1 on MacOS 9.1
> >
> > 
> ______________________________________________________________
> ____________
> > Greg Jefferis,                          Lab Address: Liqun 
> Luo, Herrin 144
> > Neurosciences PhD Programme &                e-mail: 
> jefferis at stanford.edu
> > Dept Biological Sciences,                       Lab: (650) 725 5809
> > Gilbert Biology Building,                       Fax: (650) 723 0589
> > 371 Serra Mall,
> > Stanford, CA 94305-5020.                       Home: (650) 497 1135
> >
> > 
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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