Combine two polygon arrays with a set operation

Each function pairs x with y row by row and returns the polygonal result. y is recycled against x.

Usage

ga_boolean_intersection(x, y)

ga_boolean_union(x, y)

ga_boolean_difference(x, y)

ga_boolean_xor(x, y)

Arguments

x

a GeoArrow polygon or multipolygon array

y

a GeoArrow polygon or multipolygon array; length 1 or the same length as x

Value

a GeoArrow multipolygon array of the same length as x

Details

ga_boolean_intersection() keeps the area in both, ga_boolean_union() the area in either, ga_boolean_difference() the area in x but not y, and ga_boolean_xor() the area in exactly one of them.

These are defined for polygons and multipolygons only. A row whose geometry is any other type, or is null, comes back null. The result is always a multipolygon, since a set operation can split one polygon into several or erase it entirely.

References

BooleanOps

See also

Other boolean: ga_unary_union()

Examples

x <- geoarrow::as_geoarrow_array(sf::st_sfc(
  sf::st_polygon(list(rbind(c(0, 0), c(2, 0), c(2, 2), c(0, 2), c(0, 0))))
))
y <- geoarrow::as_geoarrow_array(sf::st_sfc(
  sf::st_polygon(list(rbind(c(1, 1), c(3, 1), c(3, 3), c(1, 3), c(1, 1))))
))

# two 2x2 squares offset by 1, so the overlap is a 1x1 square
as.vector(ga_unsigned_area(ga_boolean_intersection(x, y)))
#> [1] 1