rgeos (version 0.3-5)

gDifference: Geometry Difference

Description

Function for determining the difference between the two given geometries.

Usage

gDifference(spgeom1, spgeom2, byid=FALSE, id=NULL, drop_not_poly=FALSE)

Arguments

spgeom1, spgeom2

sp objects as defined in package sp

byid

Logical vector determining if the function should be applied across ids (TRUE) or the entire object (FALSE) for spgeom1 and spgeom2

id

Character vector defining id labels for the resulting geometries, if unspecified returned geometries will be labeled based on their parent geometries' labels.

drop_not_poly

default FALSE, if TRUE and spgeom1, spgeom2 both inherit from SpatialPolygons, POINT and LINESTRING objects will be dropped from output GEOMETRYCOLLECTION objects to simplify output.

Details

Returns the regions of spgeom1 that are not within spgeom2. If the geometries do not intersect then the result is just spgeom1. Note that the function is not symmetric for spgeom1 and spgeom2.

See Also

gIntersection gSymdifference gUnion

Examples

x = readWKT("POLYGON ((0 0, 0 10, 10 10, 10 0, 0 0))")
y = readWKT("POLYGON ((3 3, 7 3, 7 7, 3 7, 3 3))")

d = gDifference(x,y)
plot(d,col='red',pbg='white')

# Empty geometry since y is completely contained with x
d2 = gDifference(y,x)