[R] Finding a 3D convex hull in R

[Prof Brian D Ripley]

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
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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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