Identify 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)

## Arguments

x

SpatRaster

cells

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

directions

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

pairs

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

include

logical. Should the focal cells be included in the result?

type

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

symmetrical

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

relate, nearby

matrix

## Examples

r <- rast(nrows=10, ncols=10)
#>    [,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")
#>    [,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)
#>    [,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")
#>    [,1] [,2] [,3] [,4]
#> 10    1   20   12   21

f <- system.file("ex/lux.shp", package="terra")
v <- vect(f)