Hi Alex I think the following might be close to what you want; 1) calculate the convex hull of your point set 2) Calculate the centroid of the convex hull polygon 3) for each point: calculate the distance to the centroid (d_c) calculate the distance to the closest boundary (d_b) 4) interior = d_c < d_b
If this simple 50/50 rule is to simple, you could use convex hull peeling to determine the exterior points for some threshold, eg the outer 30% of the data. hope this helps Nicholas > ---------------------------------------------------------------------- > > Message: 1 > Date: Wed, 29 Apr 2009 12:12:42 +0200 > From: Alexandre VILLERS <[email protected]> > Subject: [R-sig-Geo] Characterizing the position (central vs > peripheral) of a point in a point pattern > To: Aide R SIG GEO <[email protected]> > Message-ID: <[email protected]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Good morning, > > I would like to characterize the position of a given nest in a > population of breeding birds. Does anyone know a statisitics (and > associated R package) that could objectively tell whether a nest has a > central or peripheral location ? It also needs to be density independent > (not affected by sample size) > Hope this is a trivial question ! > > Thanks for your help. > > Alex > > -- > Alexandre Villers > PhD Student > Team "Biodiversity" > Centre d'Etudes Biologiques de Chiz?-CNRS UPR1934 > 79360 Beauvoir sur Niort > > Phone +33 (0)5 49 09 96 13 > Fax +33 (0)5 49 09 65 26 > > > > > __________ Information from ESET Mail Security, version of virus > signature database 4042 (20090429) __________ > > The message was checked by ESET Mail Security. > http://www.eset.com > > _______________________________________________ R-sig-Geo mailing list [email protected] https://stat.ethz.ch/mailman/listinfo/r-sig-geo
