Compute the Unary Union of "SpatialPolygons"

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

Usage

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

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. The alternative method="gpclib" via package maptools is no longer provided in surveillance > 1.20.3.

...

further arguments passed to the chosen method.

Value

an object of class

"SpatialPolygons" representing the union of all subpolygons.

Author

Sebastian Meyer

See also

gUnaryUnion in package rgeos, polyclip in package polyclip.

Examples

## Load districts of Germany
load(system.file("shapes", "districtsD.RData", package = "surveillance"))
plot(districtsD, border = "gray", asp = 1)  

## 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)
}