topo-unary-gPolygonize: Linestring Polygonizer In rgeos: Interface to Geometry Engine - Open Source ('GEOS')

 gPolygonize R Documentation

Linestring Polygonizer

Description

Function attempts to polygonize the given list of linestrings. If the linestrings are not noded (coordinates inserted at intersection points), the function may fail. `gNode` may be tried to insert such missing points

Usage

``````	gPolygonize( splist, getCutEdges=FALSE);
``````

Arguments

 `splist` a list of sp SpatialLines objects `getCutEdges` Logical vector indicating if cut edges should be 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.

Value

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

Author(s)

Roger Bivand & Colin Rundel

`gNode`

Examples

``````library(sp)
linelist = list(readWKT("LINESTRING (0 0 , 10 10)"),
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")

for(i in 2:length(linelist)) {
}

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
# bug fix 130206
LS = list(