sf (version 0.7-2)

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, ...)
st_length(x)
st_distance(x, y, ..., dist_fun, by_element = FALSE,
  which = "distance", 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; if equal to Haussdorf or Frechet, Hausdorff resp. Frechet distances are returned

par

for which equal to Haussdorf or Frechet, use a positive value this 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 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.

Details

great circle distance calculations use function geod_inverse from proj.4 if proj.4 is at version larger than 4.8.0, or else the Vincenty method implemented in liblwgeom (this should correspond to what PostGIS does).

See Also

st_dimension, st_cast to convert geometry types

Examples

# NOT RUN {
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)
# }