Re: [R] Concave hull

Hi, I just want to add a possible solution to the problem in the special case all the points must stay on the edge of the outline. THis is sometimes the case when doing image analysis and you want to order the points along a closed path. In this specific case, you can use some algorithm like the

Re: [R] Concave hull

Thanks for the interesting reference to alphahull. It might be a good starting point for placing e.g. a legend in a plot (I think the usual techniques for this (gregmisc?) are a bit more brute-force.) baptiste 2009/11/27 Kjetil Halvorsen kjetilbrinchmannhalvor...@gmail.com: There is a package

Re: [R] Concave hull

Dear David and other concave-hull-ists, yes, I meant concave hulls indeed. I know about the algorithm mentioed (www.concavehull.com) but it is not open source, so you cannot integrate it in R, and it is apparently patented, so even if you find the description you cannot apply it to implement

Re: [R] Concave hull

On 26/11/2009 4:02 AM, Corrado Topi wrote: Dear David and other concave-hull-ists, yes, I meant concave hulls indeed. I know about the algorithm mentioed (www.concavehull.com) but it is not open source, so you cannot integrate it in R, and it is apparently patented, so even if you find the

Re: [R] Concave hull

Raising a rather general question here. This is a tantalising discussion, but the notion of concave hull strikes me as extremely ill-defined! I'd like to see statement of what it is (generically) supposed to be. The examples discussed so far seem to rely on a person's inner feelings of what it

Re: [R] Concave hull

2009/11/26 Ted Harding ted.hard...@manchester.ac.uk: Raising a rather general question here. This is a tantalising discussion, but the notion of concave hull strikes me as extremely ill-defined! I'd like to see statement of what it is (generically) supposed to be. I'm curious too, but I can

Re: [R] Concave hull

On 26-Nov-09 21:11:02, baptiste auguie wrote: 2009/11/26 Ted Harding ted.hard...@manchester.ac.uk: Raising a rather general question here. This is a tantalising discussion, but the notion of concave hull strikes me as extremely ill-defined! I'd like to see statement of what it is

Re: [R] Concave hull

On Thu, Nov 26, 2009 at 9:45 PM, Ted Harding ted.hard...@manchester.ac.uk wrote: So it is still an undefined solution. As is yours -- since you might want to use different radii of spheres from different directions. I think the formal and rigorous definition is a nice polygon that goes round

Re: [R] Concave hull

There is a package on CRAN implementing such an idea: alphahull, phull is other package, kjetil On Thu, Nov 26, 2009 at 6:11 PM, baptiste auguie baptiste.aug...@googlemail.com wrote: 2009/11/26 Ted Harding ted.hard...@manchester.ac.uk: Raising a rather general question here. This is a

Re: [R] Concave hull

See the function 'convhulln' in the 'geometry' package. It uses this algorithm : http://www.qhull.org/ remko - Remko Duursma Post-Doctoral Fellow Centre for Plants and the Environment University of Western Sydney Hawkesbury Campus Richmond NSW

Re: [R] Concave hull

On Wed, Nov 25, 2009 at 11:39 PM, Remko Duursma remkoduur...@gmail.com wrote: See the function 'convhulln' in the 'geometry' package. It uses this algorithm : http://www.qhull.org/ That looks like a CONVEX hull, the original poster asked about CONCAVE hulls (and in all CAPS to emphasise

Re: [R] Concave hull

Oh right I think I did not catch that *because of* the caps. Sorry. r - Remko Duursma Post-Doctoral Fellow Centre for Plants and the Environment University of Western Sydney Hawkesbury Campus Richmond NSW 2753 Dept of Biological Science

Re: [R] Concave hull

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) ) )

Re: [R] Concave hull

Drats; Forgot the plot: xx - runif(100, 0, 1) xx - runif(100, -1, 1) yy - abs(xx)+rnorm(100,0,.2); plot(xx,yy, xlim=c( min(xx)-sd(xx), max(xx)+sd(xx)), ylim =c( min(yy)-sd(yy), max(yy)+sd(yy))) dens2 - kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx), min(yy)- sd(yy), max(yy)+sd(yy) )

Re: [R] Concave hull

On Nov 25, 2009, at 7:51 PM, David Winsemius wrote: Drats; Forgot the plot: xx - runif(100, -1, 1) yy - abs(xx)+rnorm(100,0,.2); plot(xx,yy, xlim=c( min(xx)-sd(xx), max(xx)+sd(xx)), ylim =c( min(yy)-sd(yy), max(yy)+sd(yy))) dens2 - kde2d(xx, yy, lims=c(min(xx)-sd(xx), max(xx)+sd(xx),

Re: [R] Concave Hull

Message: 64 Date: Mon, 19 Jan 2009 15:14:34 -0700 From: Greg Snow greg.s...@imail.org Subject: Re: [R] Concave Hull To: Michael Kubovy kub...@virginia.edu, r-help r-help@r-project.org Message-ID: b37c0a15b8fb3c468b5bc7ebc7da14cc61c8360...@lp-exmbvs10.co.ihc.com Content-Type

Re: [R] Concave Hull

folks would have a ready answer. Perhaps a follow-up there would be a reasonable next step? -- David Winsemius On Jan 20, 2009, at 6:37 PM, Charles Geyer wrote: Message: 64 Date: Mon, 19 Jan 2009 15:14:34 -0700 From: Greg Snow greg.s...@imail.org Subject: Re: [R] Concave Hull To: Michael Kubovy

Re: [R] Concave Hull

step? -- David Winsemius On Jan 20, 2009, at 6:37 PM, Charles Geyer wrote: Message: 64 Date: Mon, 19 Jan 2009 15:14:34 -0700 From: Greg Snow greg.s...@imail.org Subject: Re: [R] Concave Hull To: Michael Kubovy kub...@virginia.edu, r-help r-help@r-project.org Message-ID

Re: [R] Concave Hull

I don't know if it is the same algorithm or not, but there is the function chull that finds the convex hull. Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 -Original Message- From: