geos_unary

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Geometric unary operations on simple feature geometry sets

Geometric unary operations on simple feature geometry sets. These are all generics, with methods for sfg, sfc and sf objects, returning an object of the same class.

Usage
st_buffer(x, dist, nQuadSegs = 30)

st_boundary(x)

st_convex_hull(x)

st_simplify(x, preserveTopology = FALSE, dTolerance = 0)

st_triangulate(x, dTolerance = 0, bOnlyEdges = FALSE)

st_voronoi(x, envelope, dTolerance = 0, bOnlyEdges = FALSE)

st_polygonize(x)

st_line_merge(x)

st_centroid(x, ..., of_largest_polygon = FALSE)

st_point_on_surface(x)

st_node(x)

st_segmentize(x, dfMaxLength, ...)

Arguments
x

object of class sfg, sfg or sf

dist

numeric; buffer distance for all, or for each of the elements in x; in case dist is a units object, it should be convertible to arc_degree if x has geographic coordinates, and to st_crs(x)$units otherwise

nQuadSegs

integer; number of segments per quadrant (fourth of a circle), for all or per-feature

preserveTopology

logical; carry out topology preserving simplification? May be specified for each, or for all feature geometries.

dTolerance

numeric; tolerance parameter, specified for all or for each feature geometry.

bOnlyEdges

logical; if TRUE, return lines, else return polygons

envelope

object of class sfc or sfg containing a POLYGON with the envelope for a voronoi diagram; this only takes effect when it is larger than the default envelope, chosen when envelope is an empty polygon

...

ignored

of_largest_polygon

logical; for st_centroid: if TRUE, return centroid of the largest (sub)polygon of a MULTIPOLYGON rather than of the whole MULTIPOLYGON

dfMaxLength

maximum length of a line segment. If x has geographical coordinates (long/lat), dfMaxLength is either a numeric expressed in meter, or an object of class units with length units or unit rad or degree; segmentation takes place along the great circle, using st_geod_segmentize.

Details

st_triangulate requires GEOS version 3.4 or above

st_voronoi requires GEOS version 3.5 or above

in case of st_polygonize, x must be an object of class LINESTRING or MULTILINESTRING, or an sfc geometry list-column object containing these

in case of st_line_merge, x must be an object of class MULTILINESTRING, or an sfc geometry list-column object containing these

st_point_on_surface returns a point guaranteed to be on the (multi)surface.

st_node adds nodes to linear geometries at intersections without a node, and only works on individual linear geometries

Value

an object of the same class of x, with manipulated geometry.

Aliases
  • geos_unary
  • st_buffer
  • geos_unary
  • st_boundary
  • geos_unary
  • st_convex_hull
  • geos_unary
  • st_simplify
  • geos_unary
  • st_triangulate
  • geos_unary
  • st_voronoi
  • geos_unary
  • st_polygonize
  • geos_unary
  • st_line_merge
  • geos_unary
  • st_centroid
  • geos_unary
  • st_point_on_surface
  • geos_unary
  • st_node
  • geos_unary
  • st_segmentize
Examples
# NOT RUN {
nc = st_read(system.file("shape/nc.shp", package="sf"))
plot(st_convex_hull(nc))
plot(nc, border = grey(.5))
set.seed(1)
x = st_multipoint(matrix(runif(10),,2))
box = st_polygon(list(rbind(c(0,0),c(1,0),c(1,1),c(0,1),c(0,0))))
if (sf_extSoftVersion()["GEOS"] >= "3.5.0") {
 v = st_sfc(st_voronoi(x, st_sfc(box)))
 plot(v, col = 0, border = 1, axes = TRUE)
 plot(box, add = TRUE, col = 0, border = 1) # a larger box is returned, as documented
 plot(x, add = TRUE, col = 'red', cex=2, pch=16)
 plot(st_intersection(st_cast(v), box)) # clip to smaller box
 plot(x, add = TRUE, col = 'red', cex=2, pch=16)
}
mls = st_multilinestring(list(matrix(c(0,0,0,1,1,1,0,0),,2,byrow=TRUE)))
st_polygonize(st_sfc(mls))
mls = st_multilinestring(list(rbind(c(0,0), c(1,1)), rbind(c(2,0), c(1,1))))
st_line_merge(st_sfc(mls))
plot(nc, axes = TRUE)
plot(st_centroid(nc), add = TRUE, pch = 3)
mp = st_combine(st_buffer(st_sfc(lapply(1:3, function(x) st_point(c(x,x)))), 0.2 * 1:3))
plot(mp)
plot(st_centroid(mp), add = TRUE, col = 'red') # centroid of combined geometry
plot(st_centroid(mp, of_largest_polygon = TRUE), add = TRUE, col = 'blue', pch = 3)
plot(nc, axes = TRUE)
plot(st_point_on_surface(nc), add = TRUE, pch = 3)
(l = st_linestring(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0))))
st_polygonize(st_node(l))
st_node(st_multilinestring(list(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0)))))
sf = st_sf(a=1, geom=st_sfc(st_linestring(rbind(c(0,0),c(1,1)))), crs = 4326)
seg = st_segmentize(sf, units::set_units(100, km))
seg = st_segmentize(sf, units::set_units(0.01, rad))
nrow(seg$geom[[1]])
# }
Documentation reproduced from package sf, version 0.6-3, License: GPL-2 | MIT + file LICENSE

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