surveillance (version 1.20.3)

unionSpatialPolygons: Compute the Unary Union of "SpatialPolygons"

Description

Union all subpolygons of a "SpatialPolygons" object. This is a wrapper for the polygon clipping engines implemented by packages rgeos, polyclip, or gpclib.

Usage

unionSpatialPolygons(SpP, method = c("rgeos", "polyclip", "gpclib"), ...)

Value

an object of class

"SpatialPolygons" representing the union of all subpolygons.

Arguments

SpP

an object of class "SpatialPolygons". For the polyclip method only, all polygon classes for which an xylist-method exists should work as input.

method

polygon clipping machinery to use. Default is to simply call gUnaryUnion in package rgeos. For method="polyclip", function polyclip from package polyclip is used, whereas method="gpclib" calls unionSpatialPolygons in package maptools (and requires acceptance of gpclib's restricted license via surveillance.options(gpclib=TRUE)).

...

further arguments passed to the chosen method.

Author

Sebastian Meyer

See Also

gUnaryUnion in package rgeos, polyclip in package polyclip, unionSpatialPolygons in package maptools (for using union of package gpclib).

Examples

## Load districts of Germany
load(system.file("shapes", "districtsD.RData", package = "surveillance"))
plot(districtsD, border = "gray")

## Union these districts using either "rgeos" or "polyclip"
if (requireNamespace("rgeos"))  {
    stateD <- unionSpatialPolygons(districtsD, method = "rgeos")
    plot(stateD, add = TRUE, border = 2, lwd = 2)
}
if (requireNamespace("polyclip")) {
    stateD_pc <- unionSpatialPolygons(districtsD, method = "polyclip")
    plot(stateD_pc, add = TRUE, border = 1, lwd = 2, lty = 2)
}