maptools (version 1.1-8)

checkPolygonsHoles: Check holes in Polygons objects

Description

The function checks holes in Polygons objects. Use of the rgeos package functions is prefered, and if rgeos is available, they will be used automatically. In this case, member Polygon objects are checked against each other for containment, and the returned Polygons object has component hole slots set appropriately. In addition, the output Polygons object may be provided with a comment string, encoding the external and internal rings.

Usage

checkPolygonsHoles(x, properly=TRUE, avoidGEOS=FALSE, useSTRtree=FALSE)
rgeosStatus()

Value

An Polygons object re-created from the input object.

Arguments

x

An Polygons object as defined in package sp

properly

default TRUE, use gContainsProperly rather than gContains

avoidGEOS

default FALSE

useSTRtree

default FALSE, if TRUE, use rgeos STRtree in checking holes, which is much faster, but uses a lot of memory and does not release it on completion (work in progress)

Author

Roger Bivand

Examples

if (rgeosStatus()) {
nc1 <- readShapePoly(system.file("shapes/sids.shp", package="maptools")[1],
 proj4string=CRS("+proj=longlat +ellps=clrk66"))
pl <- slot(nc1, "polygons")
sapply(slot(pl[[4]], "Polygons"), function(x) slot(x, "hole"))
pl[[4]] <- Polygons(list(slot(pl[[4]], "Polygons")[[1]],
 Polygon(slot(slot(pl[[4]], "Polygons")[[2]], "coords"), hole=TRUE),
 slot(pl[[4]], "Polygons")[[3]]), slot(pl[[4]], "ID"))
sapply(slot(pl[[4]], "Polygons"), function(x) slot(x, "hole"))
pl_new <- lapply(pl, checkPolygonsHoles)
sapply(slot(pl_new[[4]], "Polygons"), function(x) slot(x, "hole"))
srs <- slot(slot(pl[[1]], "Polygons")[[1]], "coords")
hle2 <- structure(c(-81.64093, -81.38380, -81.34165, -81.66833, -81.64093, 
 36.57865, 36.57234, 36.47603, 36.47894, 36.57865), .Dim = as.integer(c(5, 2)))
hle3 <- structure(c(-81.47759, -81.39118, -81.38486, -81.46705, -81.47759, 
 36.56289, 36.55659, 36.49907, 36.50380, 36.56289), .Dim = as.integer(c(5, 2)))
x <- Polygons(list(Polygon(srs), Polygon(hle2), Polygon(hle3)),
 ID=slot(pl[[1]], "ID"))
sapply(slot(x, "Polygons"), function(x) slot(x, "hole"))
res <- checkPolygonsHoles(x)
sapply(slot(res, "Polygons"), function(x) slot(x, "hole"))
if (FALSE) {
opar <- par(mfrow=c(1,2))
SPx <- SpatialPolygons(list(x))
plot(SPx)
text(t(sapply(slot(x, "Polygons"), function(i) slot(i, "labpt"))),
 labels=sapply(slot(x, "Polygons"), function(i) slot(i, "hole")), cex=0.6)
title(xlab="Hole slot values before checking")
SPres <- SpatialPolygons(list(res))
plot(SPres)
text(t(sapply(slot(res, "Polygons"), function(i) slot(i, "labpt"))),
 labels=sapply(slot(res, "Polygons"), function(i) slot(i, "hole")), cex=0.6)
title(xlab="Hole slot values after checking")
par(opar)
p1 <- Polygon(cbind(x=c(0, 0, 10, 10, 0), y=c(0, 10, 10, 0, 0))) # I
p2 <- Polygon(cbind(x=c(3, 3, 7, 7, 3), y=c(3, 7, 7, 3, 3))) # H
p8 <- Polygon(cbind(x=c(1, 1, 2, 2, 1), y=c(1, 2, 2, 1, 1))) # H
p9 <- Polygon(cbind(x=c(1, 1, 2, 2, 1), y=c(5, 6, 6, 5, 5))) # H
p3 <- Polygon(cbind(x=c(20, 20, 30, 30, 20), y=c(20, 30, 30, 20, 20))) # I
p4 <- Polygon(cbind(x=c(21, 21, 29, 29, 21), y=c(21, 29, 29, 21, 21))) # H
p14 <- Polygon(cbind(x=c(21, 21, 29, 29, 21), y=c(21, 29, 29, 21, 21))) # H
p5 <- Polygon(cbind(x=c(22, 22, 28, 28, 22), y=c(22, 28, 28, 22, 22))) # I
p15 <- Polygon(cbind(x=c(22, 22, 28, 28, 22), y=c(22, 28, 28, 22, 22))) # I
p6 <- Polygon(cbind(x=c(23, 23, 27, 27, 23), y=c(23, 27, 27, 23, 23))) # H
p7 <- Polygon(cbind(x=c(13, 13, 17, 17, 13), y=c(13, 17, 17, 13, 13))) # I
p10 <- Polygon(cbind(x=c(24, 24, 26, 26, 24), y=c(24, 26, 26, 24, 24))) # I
p11 <- Polygon(cbind(x=c(24.25, 24.25, 25.75, 25.75, 24.25),
 y=c(24.25, 25.75, 25.75, 24.25, 24.25))) # H
p12 <- Polygon(cbind(x=c(24.5, 24.5, 25.5, 25.5, 24.5),
 y=c(24.5, 25.5, 25.5, 24.5, 24.5))) # I
p13 <- Polygon(cbind(x=c(24.75, 24.75, 25.25, 25.25, 24.75),
 y=c(24.75, 25.25, 25.25, 24.75, 24.75))) # H
lp <- list(p1, p2, p13, p7, p6, p5, p4, p3, p8, p11, p12, p9, p10, p14, p15)
#           1   2    3   4   5   6   7   8   9   10   11  12   13   14   15
#           0   1   11   0   6   0   8   0   1   13    0   1    0  (7)  (6)
#           I   H    H   I   H   I   H   I   H    H    I   H    I   ?    ?
pls <- Polygons(lp, ID="1")
comment(pls)
pls1 <- checkPolygonsHoles(pls)
comment(pls1)
opar <- par(mfrow=c(1,2))
plot(SpatialPolygons(list(pls)), col="magenta", pbg="cyan", usePolypath=FALSE)
title(xlab="Hole slot values before checking")
plot(SpatialPolygons(list(pls1)), col="magenta", pbg="cyan", usePolypath=FALSE)
title(xlab="Hole slot values after checking")
par(opar)
}
}