topo-unary-gNode: Linestring Noder

In rgeos: Interface to Geometry Engine - Open Source ('GEOS')

Linestring Noder

Description

Function attempts to node a linestring object, inserting coordinates at intersection points; only available for GEOS >= 3.4.0.

Usage

	gNode(spgeom);

Arguments

spgeom

an sp object inheriting from SpatialLines

Details

Because gPolygonize expects linestrings to be fully noded, as such they must not cross and must touch only at endpoints. gNodee takes an object inheriting from SpatialLines and attempts to add omitted nodes. Issue reported by Nicola Farina 21 March 2014.

Value

Returns a noded linestring object.

Author(s)

Roger Bivand

See Also

gPolygonize

Examples

library(sp)
pol1 <- readWKT(paste("POLYGON((39.936 43.446, 39.94 43.446, 39.94 43.45,",
 "39.936 43.45, 39.936 43.446))"))
pol2 <- readWKT(paste("POLYGON((39.9417 43.45, 39.9395 43.4505,",
 "39.9385 43.4462, 39.9343 43.4452, 39.9331 43.4469, 39.9417 43.45))"))
plot(pol2, axes=TRUE)
plot(pol1, add=TRUE, border="blue")
gIsValid(pol1)
gIsValid(pol2)
try(res <- gUnion(pol1, pol2))
if (version_GEOS0() > "3.4.0") {
pol2a <- gPolygonize(gNode(as(pol2, "SpatialLines")))
try(res <- gUnion(pol1, pol2a))
plot(res, add=TRUE, border="red", lty=2, lwd=2)
set.seed(1)
# rw from Jim Holtman's R-help posting 2010-12-2
n <- 1000
rw <- matrix(0, ncol = 2, nrow = n)
indx <- cbind(seq(n), sample(c(1, 2), n, TRUE))
rw[indx] <- sample(c(-1, 1), n, TRUE)
rw[,1] <- cumsum(rw[, 1])
rw[, 2] <- cumsum(rw[, 2])
slrw <- SpatialLines(list(Lines(list(Line(rw)), "1")))
res0 <- gNode(slrw)
print(length(slrw))
print(length(res0))
res <- gPolygonize(res0)
print(summary(res))
print(length(res))
plot(res0, axes=TRUE)
plot(res, add=TRUE, col=sample(rainbow(length(res))))
# library(spatstat)
# set.seed(0)
# X <- psp(runif(100), runif(100), runif(100), runif(100), window=owin())
# library(maptools)
# sppsp <- as(X, "SpatialLines")
# writeLines(writeWKT(sppsp, byid=FALSE), con="sppsp.wkt")
sppsp <- readWKT(readLines(system.file("wkts/sppsp.wkt", package="rgeos")))
plot(sppsp, axes=TRUE)
res0 <- gNode(sppsp)
res <- gPolygonize(res0)
plot(res, add=TRUE, col=sample(rainbow(length(res))))
}

rgeos documentation built on July 26, 2023, 5:42 p.m.