Compute DE9-IM relation between pairs of geometries, or match it to a given pattern

st_relate(x, y, pattern = NA_character_, sparse = !is.na(pattern))

Arguments

x	object of class `sf`, `sfc` or `sfg`
y	object of class `sf`, `sfc` or `sfg`
pattern	character; define the pattern to match to, see details.
sparse	logical; should a sparse matrix be returned (TRUE) or a dense matrix?

Value

In case pattern is not given, st_relate returns a dense character matrix; element [i,j] has nine characters, referring to the DE9-IM relationship between x[i] and y[j], encoded as IxIy,IxBy,IxEy,BxIy,BxBy,BxEy,ExIy,ExBy,ExEy where I refers to interior, B to boundary, and E to exterior, and e.g. BxIy the dimensionality of the intersection of the the boundary of x[i] and the interior of y[j], which is one of 0,1,2,F, digits denoting dimensionality, F denoting not intersecting. When pattern is given, a dense logical matrix or sparse index list returned with matches to the given pattern; see st_intersection for a description of the returned matrix or list. See also https://en.wikipedia.org/wiki/DE-9IM for further explanation.

Examples

p1 = st_point(c(0,0))
p2 = st_point(c(2,2))
pol1 = st_polygon(list(rbind(c(0,0),c(1,0),c(1,1),c(0,1),c(0,0)))) - 0.5
pol2 = pol1 + 1
pol3 = pol1 + 2
st_relate(st_sfc(p1, p2), st_sfc(pol1, pol2, pol3))
#>      [,1]        [,2]        [,3]       
#> [1,] "0FFFFF212" "FF0FFF212" "FF0FFF212"
#> [2,] "FF0FFF212" "FF0FFF212" "0FFFFF212"
sfc = st_sfc(st_point(c(0,0)), st_point(c(3,3)))
grd = st_make_grid(sfc, n = c(3,3))
st_intersects(grd)
#> Sparse geometry binary predicate list of length 2, where the predicate was `intersects'
#>  1: 1
#>  2: 2
st_relate(grd, pattern = "****1****") # sides, not corners, internals
#> Sparse geometry binary predicate list of length 2, where the predicate was `relate_pattern'
#>  1: 1
#>  2: 2
st_relate(grd, pattern = "****0****") # only corners touch
#> Sparse geometry binary predicate list of length 2, where the predicate was `relate_pattern'
#>  1: (empty)
#>  2: (empty)
st_rook = function(a, b = a) st_relate(a, b, pattern = "F***1****")
st_rook(grd)
#> Sparse geometry binary predicate list of length 2, where the predicate was `relate_pattern'
#>  1: (empty)
#>  2: (empty)
# queen neighbours, see \url{https://github.com/r-spatial/sf/issues/234#issuecomment-300511129}
st_queen <- function(a, b = a) st_relate(a, b, pattern = "F***T****")