surveillance (version 1.24.0)

unionSpatialPolygons: Compute the Unary Union of "SpatialPolygons"

Description

Union all subpolygons of a "SpatialPolygons" object. This is a legacy wrapper for the polygon clipping engines implemented by packages sf and polyclip. Internally, both methods need to convert the input polygons to a class appropriate for the method, so are rather inefficient.

Usage

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

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 call st_union in package sf. For method="polyclip", function polyclip from package polyclip is used. The old method="gpclib" is no longer available.

...

further arguments passed to the chosen method.

Author

Sebastian Meyer

See Also

st_union in package sf, 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 "sf" or "polyclip"
if (requireNamespace("sf"))  {
    stateD <- unionSpatialPolygons(districtsD, method = "sf")
    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)
}