On 06/09/2010 11:01 PM, Dylan Beaudette wrote:
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.
A combination of lapply and do.call("rbind" also works well in terms of
performance.
cheers,
Paul
Cheers,
Dylan
--
Drs. Paul Hiemstra
Department of Physical Geography
Faculty of Geosciences
University of Utrecht
Heidelberglaan 2
P.O. Box 80.115
3508 TC Utrecht
Phone: +3130 274 3113 Mon-Tue
Phone: +3130 253 5773 Wed-Fri
http://intamap.geo.uu.nl/~paul
http://nl.linkedin.com/pub/paul-hiemstra/20/30b/770
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