sf (version 0.4-3)

st_sample: sample points on or in (sets of) spatial features

Description

sample points on or in (sets of) spatial features

Usage

st_sample(x, size, ..., type = "random")

Arguments

x

object of class sf or sfc

size

sample size(s) requested; either total size, or a numeric vector with sample sizes for each feature geometry. When sampling polygons, the returned sampling size may differ from the requested size, as the bounding box is sampled, and sampled points intersecting the polygon are returned.

...

ignored, or passed on to sample for multipoint sampling

type

character; indicates the spatial sampling type; only random is implemented right now

Details

if x has dimension 2 (polygons) and geographical coordinates (long/lat), uniform random sampling on the sphere is applied, see e.g. http://mathworld.wolfram.com/SpherePointPicking.html

Examples

x = st_sfc(st_polygon(list(rbind(c(0,0),c(90,0),c(90,90),c(0,90),c(0,0)))), crs = st_crs(4326))
plot(x, axes = TRUE, graticule = TRUE)
plot(p <- st_sample(x, 1000), add = TRUE)
x2 = st_transform(st_segmentize(x,1e4), st_crs("+proj=ortho +lat_0=30 +lon_0=45"))
g = st_transform(st_graticule(), st_crs("+proj=ortho +lat_0=30 +lon_0=45"))
plot(x2, graticule = g)
p2 = st_transform(p, st_crs("+proj=ortho +lat_0=30 +lon_0=45"))
plot(p2, add = TRUE)
x = st_sfc(st_polygon(list(rbind(c(0,0),c(90,0),c(90,90),c(0,90),c(0,0))))) # NOT long/lat:
plot(x)
plot(st_sample(x, 1000), add = TRUE)
x = st_sfc(st_polygon(list(rbind(c(-180,-90),c(180,-90),c(180,90),c(-180,90),c(-180,-90)))),
 crs=st_crs(4326))
p = st_sample(x, 1000)
pt = st_multipoint(matrix(1:20,,2))
st_sample(p, 3)
ls = st_sfc(st_linestring(rbind(c(0,0),c(0,1))),
 st_linestring(rbind(c(0,0),c(.1,0))),
 st_linestring(rbind(c(0,1),c(.1,1))),
 st_linestring(rbind(c(2,2),c(2,2.00001))))
st_sample(ls, 80)