rgeos (version 0.2-4)

gPolygonize: Linestring Polygonizer

Description

Function attempts to polygonize the given list of linestrings

Usage

gPolygonize( splist, getCutEdges=FALSE);

Arguments

splist

a list of sp objects

getCutEdges

Logical vector indicating if cut edges should be returned

Value

• By default returns polygons generated by polygonizing the given linestrings. If getCutEdges is TRUE then any cut edges are returned.

Details

Polygonization is the process of forming polygons from linestrings which enclose an area. Linestrings are expected to be fully noded, as such they must not cross and must touch only at endpoints. gPolygonize takes a list of fully noded linestrings and forms all the polygons which are enclosed by the lines. Polygonization errors such as dangling lines or cut lines can be identified and reported.

Examples

linelist = list(readWKT("LINESTRING (0 0 , 10 10)"),
				readWKT("LINESTRING (185 221, 100 100)"),
				readWKT("LINESTRING (185 221, 88 275, 180 316)"),
				readWKT("LINESTRING (185 221, 292 281, 180 316)"), 
				readWKT("LINESTRING (189 98, 83 187, 185 221)"), 
				readWKT("LINESTRING (189 98, 325 168, 185 221)"))

par(mfrow=c(1,2))
plot(linelist[[1]],xlim=c(0,350),ylim=c(0,350))
title("Linestrings with nodes")
plot(as(linelist[[1]],"SpatialPoints"),pch=16,add=TRUE)

for(i in 2:length(linelist)) {
	plot(linelist[[i]],add=TRUE)
	plot(as(linelist[[i]],"SpatialPoints"),pch=16,add=TRUE)
}

plot(gPolygonize(linelist),xlim=c(0,350),ylim=c(0,350))
title("Polygonized Results")

gPolygonize(linelist,getCutEdges=TRUE) # no cut edges



linelist2 = list(readWKT("LINESTRING(1 3, 3 3, 3 1, 1 1, 1 3)"),
				 readWKT("LINESTRING(1 3, 3 3, 3 1, 1 1, 1 3)"))

gPolygonize(linelist2,getCutEdges=FALSE) # NULL
gPolygonize(linelist2,getCutEdges=TRUE) # Contains LineStrings