[R-sig-Geo] How to extract coordinates values from a shapefile?

[Hadley Wickham]

On Wed, Jun 9, 2010 at 3:24 PM, Edzer Pebesma
<edzer.pebesma at uni-muenster.de> wrote:
> The example provided by Matt assumes that each polygon consists of a
> single ring, and doesn't have islands, lakes etc. The function below
> pasts all coordinates to a single 2-column matrix. For clarity's sake, I
> avoided nested sapply's.
>
> library(maptools)
> xx <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
>  IDvar="FIPSNO", proj4string=CRS("+proj=longlat +ellps=clrk66"))
> allcoordinates = function(x) {
>    ret = NULL
>    polys = x at polygons
>    for(i in 1:length(polys)) {
>        pp = polys[[i]]@Polygons
>        for (j in 1:length(pp))
>            ret = rbind(ret, coordinates(pp[[j]]))
>    }
>    ret
> }
> q = allcoordinates(xx)
>
> # check:
> plot(xx)
> lines(q, col='blue')

And that's basically what fortify does, except it covers a few more cases.

Hadley

-- 
Assistant Professor / Dobelman Family Junior Chair
Department of Statistics / Rice University
http://had.co.nz/