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Binary operations on WKB or WKT geometries

Source: R/geom.R
g_binary_op.Rd

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

Usage

g_intersection(
  this_geom,
  other_geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_union(
  this_geom,
  other_geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_difference(
  this_geom,
  other_geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

g_sym_difference(
  this_geom,
  other_geom,
  as_wkb = TRUE,
  as_iso = FALSE,
  byte_order = "LSB",
  quiet = FALSE
)

Arguments

this_geom

Either a raw vector of WKB or list of raw vectors, or a character vector containing one or more WKT strings.

other_geom

Either a raw vector of WKB or list of raw vectors, or a character vector containing one or more WKT strings. Must contain the same number of geometries as this_geom.

as_wkb

Logical, TRUE to return the output geometry in WKB format (the default), or FALSE to return as WKT.

as_iso

Logical, TRUE to export as ISO WKB/WKT (ISO 13249 SQL/MM Part 3), or FALSE (the default) to export as "Extended WKB/WKT".

byte_order

Character string specifying the byte order when output is WKB. One of "LSB" (the default) or "MSB" (uncommon).

quiet

Logical, TRUE to suppress warnings. Defaults to FALSE.

Value

A geometry as WKB raw vector or WKT string, or a list/character vector of geometries as WKB/WKT with length equal to the number of input geometry pairs. NA is returned with a warning if an input geometry cannot be converted into an OGR geometry object, or if an error occurs in the call to the underlying OGR API function.

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

this_geom and other_geom are assumed to be in the same coordinate reference system.

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