adjacent.RdIdentify cells that are adjacent to a set of raster cells. Or identify adjacent polygons
# S4 method for SpatRaster
adjacent(x, cells, directions="rook", pairs=FALSE, include=FALSE, symmetrical=FALSE)
# S4 method for SpatVector
adjacent(x, type="rook", pairs=TRUE, symmetrical=FALSE)SpatRaster
vector of cell numbers for which adjacent cells should be found. Cell numbers start with 1 in the upper-left corner and increase from left to right and from top to bottom
character or matrix to indicated the directions in which cells are considered connected. The following character values are allowed: "rook" or "4" for the horizontal and vertical neighbors; "bishop" to get the diagonal neighbors; "queen" or "8" to get the vertical, horizontal and diagonal neighbors; or "16" for knight and one-cell queen move neighbors. If directions is a matrix it should have odd dimensions and have logical (or 0, 1) values
logical. If TRUE, a two-column matrix of pairs of adjacent cells is returned. If x is a SpatRaster and pairs is FALSE, an n*m matrix is returned where the number of rows n is length(cells) and the number of columns m is the number of neighbors requested with directions
logical. Should the focal cells be included in the result?
character. One of "rook", "queen", "touches", or "intersects". "queen" and "touches" are synonyms. "rook" exclude polygons that touch at a single node only. "intersects" includes polygons that touch or overlap
logical. If TRUE and pairs=TRUE, an adjacent pair is only included once. For example, if polygon 1 is adjacent to polygon 3, the implied adjacency between 3 and 1 is not reported
matrix
r <- rast(nrows=10, ncols=10)
adjacent(r, cells=c(1, 5, 55), directions="queen")
#> [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8]
#> 0 NaN NaN NaN 10 2 20 11 12
#> 4 NaN NaN NaN 4 6 14 15 16
#> 54 44 45 46 54 56 64 65 66
r <- rast(nrows=10, ncols=10, crs="+proj=utm +zone=1 +datum=WGS84")
adjacent(r, cells=11, directions="rook")
#> [,1] [,2] [,3] [,4]
#> 10 1 NaN 12 21
#same as
rk <- matrix(c(0,1,0,1,0,1,0,1,0), 3, 3)
adjacent(r, cells=11, directions=rk)
#> [,1] [,2] [,3] [,4]
#> 10 1 NaN 12 21
## note that with global lat/lon data the E and W connect
r <- rast(nrows=10, ncols=10, crs="+proj=longlat +datum=WGS84")
adjacent(r, cells=11, directions="rook")
#> [,1] [,2] [,3] [,4]
#> 10 1 20 12 21
f <- system.file("ex/lux.shp", package="terra")
v <- vect(f)
a <- adjacent(v, symmetrical=TRUE)
head(a)
#> from to
#> [1,] 1 2
#> [2,] 1 4
#> [3,] 1 5
#> [4,] 2 3
#> [5,] 2 4
#> [6,] 2 5