Hi, Here is another approach, using something like a 'concave hull' -- i.e. alpha shapes:
http://casoilresource.lawr.ucdavis.edu/drupal/node/919 Cheers, Dylan On Friday 23 April 2010, Roman Luštrik wrote: > How does this function sound (convexhull.xy {spatstat})? > > http://bm2.genes.nig.ac.jp/RGM2/R_current/library/spatstat/man/convexhull.x >y.html > > Convex Hull of Points Description > > Computes the convex hull of a set of points in two dimensions. > Usage > > convexhull.xy(x, y=NULL) > > Arguments x vector of x coordinates of observed points, or a 2-column > matrix giving x,y coordinates, or a list with components x,y giving > coordinates (such as a point pattern object of class "ppp".) y (optional) > vector of ycoordinates of observed points, if > x is a vector. > > Cheers, > Roman > > On Fri, Apr 23, 2010 at 4:37 PM, Hans Ekbrand <h...@sociologi.cjb.net>wrote: > > How to create nice polygons from a number of clusters? > > > > I have sorted list of clusters representing hot-spots > > > > > sorted.list.of.clusters > > > > [1] 7 1 11 9 26 2 5 10 33 40 18 28 37 20 30 47 53 > > > > whereas my.cluster holds the classification of events (criminal > > fire-setting) to clusters: > > > > head(my.cluster, 100) > > [1] 1 2 3 3 4 5 6 7 8 5 9 10 11 12 1 13 2 14 15 10 16 17 5 > > 13 7 7 18 19 18 20 20 2 21 16 22 18 10 1 > > [39] 9 23 4 7 24 9 9 7 7 5 2 11 25 12 7 7 26 27 13 7 7 28 > > 18 28 29 9 2 5 30 11 31 14 18 1 32 26 2 31 > > [77] 29 33 2 34 2 26 35 36 7 2 35 37 26 38 11 2 11 26 30 7 4 11 > > 8 11 > > > > > number.of.fires.at.hotspots <- sapply(sorted.list.of.clusters, > > > > function(x) {length(which(my.cluster == x))}) > > > > > number.of.fires.at.hotspots > > > > [1] 44 39 38 32 22 21 21 21 15 15 14 14 14 12 12 12 12 > > > > The "SpatialPointsDataFrame" object clust.geo.test holds the events. > > > > A list coordinates of the events of each cluster is generated with: > > > sapply(sorted.list.of.clusters, function(x) > > > {clust.geo.t...@coords[which(my.cluster > > > > == x),]}) > > [[1]] > > Ost Nord > > [1,] 322737.4 6406939 > > [2,] 323104.9 6406968 > > [3,] 323104.9 6406968 > > ... > > > > [[2]] > > Ost Nord > > [1,] 315359.9 6393110 > > [2,] 315177.0 6394031 > > [3,] 314697.8 6394565 > > ... > > > > And I can plot the points in the hot-spots with > > > > > plot(sdn) > > > sapply(sorted.list.of.clusters, function(x) > > > > {plot(clust.geo.test[which(my.cluster == x),], add = T)}) > > > > But would like to plot each cluster as a polygon, ideally filled with > > darker colors for clusters with higher number of fires. > > > > I guess I need to create polygons for each cluster and then plot each > > polygon. How do you do that? > > > > For your convenience I have created a RData object containing the > > objects refered to above and uploaded to this URI > > > > http://sociologi.cjb.net/temp/to-polygons-help.RData, so > > > > print(load(url("http://sociologi.cjb.net/temp/to-polygons-help.RData";))) > > plot(sdn) > > sapply(sorted.list.of.clusters, function(x) > > {plot(clust.geo.test[which(my.cluster == x),], add = T)}) > > > > would get you to the point I am now. > > > > Hans Ekbrand > > > > -----BEGIN PGP SIGNATURE----- > > Version: GnuPG v1.4.9 (GNU/Linux) > > > > iEYEARECAAYFAkvRsLEACgkQfCyHKnBQYU4JrQCfWMlOgECamin5ZugGoHcUpqx3 > > fuQAoNDoG6iMVlLJCOYfoP5MRbNYHGlI > > =jKTU > > -----END PGP SIGNATURE----- > > > > _______________________________________________ > > R-sig-Geo mailing list > > R-sig-Geo@stat.math.ethz.ch > > https://stat.ethz.ch/mailman/listinfo/r-sig-geo -- Dylan Beaudette Soil Resource Laboratory http://casoilresource.lawr.ucdavis.edu/ University of California at Davis 530.754.7341 _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
