rsaga.union.polygons: Spatial union of two polygon layers
In debangs/RSAGA: SAGA Geoprocessing and Terrain Analysis in R

Description Usage Arguments Details Value Author(s) Examples

The function rsaga.union.polygons uses SAGA function "Union" to calculate the geometric union of two polygon layers. This corresponds to the intersection and the symmetrical difference of the two layers.

1 2	rsaga.union.polygons(layer_a = NULL, layer_b = NULL, result = NULL, split = FALSE, load = FALSE, env = rsaga.env())

`layer_a`	A `character`-string representing the path to a polygon shapefile or a spatial object of class `SpatialPolygonsDataFrame`.
`layer_b`	A `character`-string representing the path to a polygon shapefile or a spatial object of class `SpatialPolygonsDataFrame` with which to union layer_a.
`result`	`character`, path indicating where to store the output shapefile.
`split`	If `TRUE`, multipart polygons become separated polygons (default: FALSE).
`load`	If `TRUE`, the resulting output shapefile will be loaded into R (default: FALSE).

Function gUnion can also be used for joining intersecting polygon geometries. However, rsaga.union.polygons will be usually much faster, especially when joining thousands of polygons.

The function saves the output shapefile to the path indicated in function argument result and loads the resulting shapefile into R when function parameter load is set to TRUE.

Jannes Muenchow (R interface), Olaf Conrad and Angus Johnson (SAGA modules)

library("RSAGA")
library("sp")
# construct coordinates of two squares
coords_1 <- matrix(data = c(0, 0, 1, 0, 1, 1, 0, 1, 0, 0),
                 ncol = 2, byrow = TRUE)
coords_2 <- matrix(data = c(-0.5, -0.5, 0.5, -0.5, 0.5, 0.5, -0.5, 0.5, 
                            -0.5, -0.5),
                 ncol = 2, byrow = TRUE)
# convert the coordinates into polygons
poly_1 <- SpatialPolygons(list(Polygons(list(Polygon(coords_1)), 1)))
poly_1 <- SpatialPolygonsDataFrame(poly_1, data = data.frame(id = 1))
poly_2 <- SpatialPolygons(list(Polygons(list(Polygon(coords_2)), 1))) 
poly_2 <- SpatialPolygonsDataFrame(poly_2, data = data.frame(id_2 = 2))
# union the two polygons using SAGA and load the output
dir_tmp <- paste0(tempdir(), "/out.shp")
res <- rsaga.union.polygons(layer_a = poly_1,
                            layer_b = poly_2,
                            result = dir_tmp,
                            load = TRUE)
# output attribute table consists of three elements, i.e. the union of poly_1
# and poly_2
dim(res)
res@data