gPolygonize {rgeos} | R Documentation |
Function attempts to polygonize the given list of linestrings
gPolygonize( splist, getCutEdges=FALSE);
splist |
a list of sp objects |
getCutEdges |
Logical vector indicating if cut edges should be returned |
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.
By default returns polygons generated by polygonizing the given linestrings. If getCutEdges
is TRUE then any cut edges are returned.
Roger Bivand & Colin Rundel
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