[R] identifying lines that cross polygons.

From: Milton Cezar Ribeiro <milton_ruser_at_yahoo.com.br>
Date: Mon, 4 Feb 2008 11:07:44 -0800 (PST)


Dear All,

I have a shapefile wich contents are polygons. I sort two (here random) points and I would like to identify if the line built with this two points cross or not polygons and in case yes, which polygons were crossed. I tryed to figure out the problem with a sample code got from sp/maptools packages.

Kind regards,

Miltinho
Brazil
==
require(maptools)
grd <- GridTopology(c(1,1), c(1,1), c(10,10)) polys <- as.SpatialPolygons.GridTopology(grd) centroids <- coordinates(polys)

x <- centroids[,1]
y <- centroids[,2]
z <- 1.4 + 0.1*x + 0.2*y + 0.002*x*x

ex_1.7 <- SpatialPolygonsDataFrame(polys, data=data.frame(x=x, y=y, z=z, row.names=sapply(slot(polys, "polygons"), function(i) slot(i, "ID")))) ex_1.7.selected<-ex_1.7[c(2,5,10,25,28,23,43,55),] plot(ex_1.7.selected,axes=T,xlim=c(0,12),ylim=c(0,12)) set.seed(1)
my.lines<-NULL
for (i in 1:5) {
 df<-cbind(x=runif(2)*10,y=runif(2)*10)
 my.lines[i]<-list(df)
 lines(df,col=(i+1))
 }

 para armazenamento!

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