sf: geos_measures – R documentation

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geos_measures

Compute geometric measurements

Description

Compute Euclidian 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_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`
`...`	ignored
`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. 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.

Details

great circle distance calculations use function geod_inverse from PROJ; see Karney, Charles FF, 2013, Algorithms for geodesics, Journal of Geodesy 87(1), 43–55

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 a geometry, in the coordinate reference system used; in case x is in degrees longitude/latitude, st_geod_area is used for area calculation.

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 of length x or y, the shorter one being recycled. Distances involving empty geometries are NA.

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)
line = st_sfc(st_linestring(rbind(c(30,30), c(40,40))), crs = 4326)
st_length(line)

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))
p = st_sfc(st_point(c(0,0)), st_point(c(0,1)), st_point(c(0,2)))
st_distance(p, p)
st_distance(p, p, by_element = TRUE)

sf

Simple Features for R

v0.9-8

GPL-2 | MIT + file LICENSE

Authors

Edzer Pebesma [aut, cre] (<https://orcid.org/0000-0001-8049-7069>), Roger Bivand [ctb] (<https://orcid.org/0000-0003-2392-6140>), Etienne Racine [ctb], Michael Sumner [ctb], Ian Cook [ctb], Tim Keitt [ctb], Robin Lovelace [ctb], Hadley Wickham [ctb], Jeroen Ooms [ctb] (<https://orcid.org/0000-0002-4035-0289>), Kirill Müller [ctb], Thomas Lin Pedersen [ctb], Dan Baston [ctb]

Initial release