On Wednesday 09 June 2010, Hadley Wickham wrote:
> On Wed, Jun 9, 2010 at 3:24 PM, Edzer Pebesma
>
> <edzer.pebe...@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...@polygons
> > for(i in 1:length(polys)) {
> > pp = polys[[...@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
Not to be nit-picky, but wouldn't it be safer to pre-allocated "ret" instead
of dynamically appending? This would allow the suggested function to scale to
very large geometries.
Cheers,
Dylan
--
Dylan Beaudette
Soil Resource Laboratory
http://casoilresource.lawr.ucdavis.edu/
University of California at Davis
530.754.7341
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