[R] Concave hull

[David Winsemius]

This is not a true convave hull, but a 2D density is something similar  
and perhaps more "statistical":

library(MASS)
  xx <- runif(100, 0, 1)
  xx <- runif(100, -1, 1)
  yy <- abs(xx)+rnorm(100,0,.2)
  dens2 <- kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx),  
min(yy)-sd(yy), max(yy)+sd(yy) )  )
  contour(dens2, add=TRUE)

#  You can pick a single contour if you like:

  contour(dens2, level=0.05, col="red", add=TRUE)
  contour(dens2, level=0.10, col="blue", add=TRUE)


Happy Valentine's
-- 
David

On Nov 25, 2009, at 11:37 AM, Corrado wrote:

> Dear friends,
>
> Do you know how to calculate the CONCAVE hull of a set of points (2-
> dimensional or n-dimensional)? is that possible in R? (With a  
> "smoothing"
> parameter of course).
>
> Best,
> -- 
> Corrado Topi
>
> Global Climate Change & Biodiversity Indicators
> Area 18,Department of Biology
> University of York, York, YO10 5YW, UK
> Phone: + 44 (0) 1904 328645, E-mail: ct529 at york.ac.uk
>
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> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
Heritage Laboratories
West Hartford, CT