How does this function sound (convexhull.xy {spatstat})?
http://bm2.genes.nig.ac.jp/RGM2/R_current/library/spatstat/man/convexhull.xy.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
>
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> =jKTU
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