Binary operations on WKT geometries — g_binary

These functions implement operations on pairs of geometries in OGC WKT format.

Usage

g_intersection(this_geom, other_geom)

g_union(this_geom, other_geom)

g_difference(this_geom, other_geom)

g_sym_difference(this_geom, other_geom)

Arguments

this_geom: Character. OGC WKT string for a simple feature geometry.
other_geom: Character. OGC WKT string for a simple feature geometry.

Value

Character string. The resulting geometry as OGC WKT.

Details

These functions use the GEOS library via GDAL headers.

g_intersection() returns a new geometry which is the region of intersection of the two geometries operated on. g_intersects() can be used to test if two geometries intersect.

g_union() returns a new geometry which is the region of union of the two geometries operated on.

g_difference() returns a new geometry which is the region of this geometry with the region of the other geometry removed.

g_sym_difference() returns a new geometry which is the symmetric difference of this geometry and the other geometry (union minus intersection).

Note

Geometry validity is not checked. In case you are unsure of the validity of the input geometries, call g_is_valid() before, otherwise the result might be wrong.

Examples

elev_file <- system.file("extdata/storml_elev.tif", package="gdalraster")
ds <- new(GDALRaster, elev_file)
g1 <- ds$bbox() |> bbox_to_wkt()
ds$close()

g2 <- "POLYGON ((327381.9 5104541.2, 326824.0 5104092.5, 326708.8 5103182.9,
  327885.2 5102612.9, 329334.5 5103322.4, 329304.2 5104474.5,328212.7
  5104656.4, 328212.7 5104656.4, 327381.9 5104541.2))"

# see spatial predicate defintions at https://en.wikipedia.org/wiki/DE-9IM
g_intersects(g1, g2)  # TRUE
#> [1] TRUE
g_overlaps(g1, g2)  # TRUE
#> [1] TRUE
# therefore,
g_contains(g1, g2)  # FALSE
#> [1] FALSE

g_sym_difference(g1, g2) |> g_area()
#> [1] 14834452

g3 <- g_intersection(g1, g2)
g4 <- g_union(g1, g2)
g_difference(g4, g3) |> g_area()
#> [1] 14834452