Concave Hull
Actually, I think that the survey on "alpha shapes" available from: http://www.cs.duke.edu/~edels/Surveys/ would be more closely aligned with what Michael was interested in... url: www.econ.uiuc.edu/~roger Roger Koenker email rkoenker at uiuc.edu Department of Economics vox: 217-333-4558 University of Illinois fax: 217-244-6678 Champaign, IL 61820
On Jan 20, 2009, at 6:06 PM, David Winsemius wrote:
The OP was asking whether concave hulls have been implemented. He wasn't very helpful with his link giving the example, since it was to the "outside" of a frame-based website. Perhaps this link (see the bottom of that page) will be more helpful: http://get.dsi.uminho.pt/local/results.html It has been discussed (briefly) in r-help: http://finzi.psych.upenn.edu/R/Rhelp02a/archive/75574.html Some of the material in Loader's "Local Regression and Likelihood" regarding classification looks potentially applicable. When first I saw this question I expected that one of the r-sig-Geo 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.Snow at imail.org> Subject: Re: [R] Concave Hull To: Michael Kubovy <kubovy at virginia.edu>, r-help <r-help at r-project.org> Message-ID: <B37C0A15B8FB3C468B5BC7EBC7DA14CC61C8360835 at LP-EXMBVS10.CO.IHC.COM> Content-Type: text/plain; charset="us-ascii" I don't know if it is the same algorithm or not, but there is the function "chull" that finds the convex hull.
Also the R function "redundant" in the contributed package "rcdd" efficiently finds convex hulls in d-dimensional space for arbitrary d (chull only does d = 2). See Sections 4.2 and 5.2 of the rcdd package vignette.
Hope this helps, -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.snow at imail.org 801.408.8111
-----Original Message----- From: r-help-bounces at r-project.org [mailto:r-help-bounces at r- project.org] On Behalf Of Michael Kubovy Sent: Saturday, January 17, 2009 9:49 AM To: r-help Subject: [R] Concave Hull Dear Friends, Here is an algorithm for finding concave hulls: http://get.dsi.uminho.pt/local/ Has anyone implemented such an algorithm in R? RSiteSearch('concave hull') didn't reveal one (I think).
_____________________________ Professor Michael Kubovy University of Virginia Department of Psychology Postal Address: P.O.Box 400400, Charlottesville, VA 22904-4400 Express Parcels Address: Gilmer Hall, Room 102, McCormick Road, Charlottesville, VA 22903 Office: B011; Phone: +1-434-982-4729 Lab: B019; Phone: +1-434-982-4751 WWW: http://www.people.virginia.edu/~mk9y/ Skype name: polyurinsane [[alternative HTML version deleted]] ______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting- guide.html and provide commented, minimal, self-contained, reproducible code.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
______________________________________________ R-help at r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.