On Fri, 31 Aug 2007, Rick Reeves wrote:
Hi: look for Centroid calculations:
help.search("centroid") will show:
Help files with alias or concept or title matching 'centroid' using fuzzy matching: apply.polygon(maps) Polygon functions get.Pcent(maptools) Polygon centroids calcCentroid(PBSmapping) Calculate the Centroids of Polygons centroid.owin(spatstat) Centroid of a window affinexy(spatstat) Internal spatstat functions I suspect that the best one for your case would be centroid.owin, since it has the most straightforward input data requirements.
I agree, but am not sure that the question is about centroids. It might be the "centre" of a point pattern, where the highest density location(s) would not often be the centroid of the convex hull. If the data are SpatialPolygons read using readShapePoly() or readOGR(), the coordnates() method for the imported object returns a matrix of label points, which are the centroids of the largest member Polygon object of each Polygons object, so they can be retrieved without any more trouble, but I'm not sure that the points needed are area weighted. Roger
Hope this helps, Rick Reeves
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no