Compute geometric measurements

Compute Euclidean or great circle distance between pairs of geometries; compute, the area or the length of a set of geometries.

Usage

st_area(x, ...)

# S3 method for class 'sfc'
st_area(x, ...)

st_length(x, ...)

st_perimeter(x, ...)

st_distance(
  x,
  y,
  ...,
  dist_fun,
  by_element = FALSE,
  which = ifelse(isTRUE(st_is_longlat(x)), "Great Circle", "Euclidean"),
  par = 0,
  tolerance = 0
)

Arguments

x

object of class sf, sfc or sfg

...

passed on to s2_distance, s2_distance_matrix, or s2_perimeter

y

object of class sf, sfc or sfg, defaults to x

dist_fun

deprecated

by_element

logical; if TRUE, return a vector with distance between the first elements of x and y, the second, etc; an error is raised if x and y are not the same length. If FALSE, return the dense matrix with all pairwise distances.

which

character; for Cartesian coordinates only: one of Euclidean, Hausdorff or Frechet; for geodetic coordinates, great circle distances are computed; see details

par

for which equal to Hausdorff or Frechet, optionally use a value between 0 and 1 to densify the geometry

tolerance

ignored if st_is_longlat(x) is FALSE; otherwise, if set to a positive value, the first distance smaller than tolerance will be returned, and true distance may be smaller; this may speed up computation. In meters, or a units object convertible to meters.

Value

If the coordinate reference system of x was set, these functions return values with unit of measurement; see set_units.

st_area returns the area of each feature geometry, computed in the coordinate reference system used. In case x has geodetic coordinates (unprojected), then if sf_use_s2() is FALSE st_geod_area is used for area calculation, if it is TRUE then s2_area is used: the former assumes an ellipsoidal shape, the latter a spherical shape of the Earth. In case of projected data, areas are computed in flat space. The argument ... can be used to specify radius to s2_area, to modify the Earth radius.

st_length returns the length of a LINESTRING or MULTILINESTRING geometry, using the coordinate reference system. POINT, MULTIPOINT, POLYGON or MULTIPOLYGON geometries return zero.

If by_element is FALSE st_distance returns a dense numeric matrix of dimension length(x) by length(y); otherwise it returns a numeric vector the same length as x and y with an error raised if the lengths of x and y are unequal. Distances involving empty geometries are NA.

Details

great circle distance calculations use by default spherical distances (s2_distance or s2_distance_matrix); if sf_use_s2() is FALSE, ellipsoidal distances are computed using st_geod_distance which uses function geod_inverse from GeographicLib (part of PROJ); see Karney, Charles FF, 2013, Algorithms for geodesics, Journal of Geodesy 87(1), 43–55

See also

st_dimension, st_cast to convert geometry types

Examples

b0 = st_polygon(list(rbind(c(-1,-1), c(1,-1), c(1,1), c(-1,1), c(-1,-1))))
b1 = b0 + 2
b2 = b0 + c(-0.2, 2)
x = st_sfc(b0, b1, b2)
st_area(x)
#> [1] 4 4 4
line = st_sfc(st_linestring(rbind(c(30,30), c(40,40))), crs = 4326)
st_length(line)
#> 1435335 [m]

outer = matrix(c(0,0,10,0,10,10,0,10,0,0),ncol=2, byrow=TRUE)
hole1 = matrix(c(1,1,1,2,2,2,2,1,1,1),ncol=2, byrow=TRUE)
hole2 = matrix(c(5,5,5,6,6,6,6,5,5,5),ncol=2, byrow=TRUE)

poly = st_polygon(list(outer, hole1, hole2))
mpoly = st_multipolygon(list(
  list(outer, hole1, hole2),
  list(outer + 12, hole1 + 12)
))

st_length(st_sfc(poly, mpoly))
#> [1] 0 0
st_perimeter(poly)
#> [1] 48
st_perimeter(mpoly)
#> [1] 92
p = st_sfc(st_point(c(0,0)), st_point(c(0,1)), st_point(c(0,2)))
st_distance(p, p)
#>      [,1] [,2] [,3]
#> [1,]    0    1    2
#> [2,]    1    0    1
#> [3,]    2    1    0
st_distance(p, p, by_element = TRUE)
#> [1] 0 0 0