[R] Finding a 3D convex hull in R
Prof Brian D Ripley
ripley at stats.ox.ac.uk
Sat Sep 22 08:52:56 CEST 2001
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.
is one place I considered starting, but note the portability comments.
> Very many thanks for any suggestions,
> 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)
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