rgeos (version 0.5-1)

gDifference: Geometry Difference

Description

Function for determining the difference between the two given geometries.

Usage

gDifference(spgeom1, spgeom2, byid=FALSE, id=NULL, drop_lower_td=FALSE,
 unaryUnion_if_byid_false=TRUE, checkValidity=NULL)

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_lower_td

default FALSE; if TRUE, objects will be dropped from output GEOMETRYCOLLECTION objects to simplify output if their topological dinension is less than the minimum topological dinension of the input objects.

unaryUnion_if_byid_false

default TRUE; if byid takes a FALSE in either position, the subgeometries are combined first to avoid possible topology exceptions (change in 0.3-13, previous behaviour did not combine subgeometries, and may be achieved by setting this argument FALSE

checkValidity

default NULL, integer 0L (no action), 1L (check), 2L (check and try to buffer by zero distance to repair). If NULL, a value set to 0L for GEOS < 3.7.2, 1L for GEOS >= 3.7.2 is read from values assigned on load. Error meesages from GEOS do not say clearly which object fails if a topology exception is encountered. If this argument is > 0L, gIsValid is run on each in turn

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

# NOT RUN {
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)
# }