geos_unary: Geometric unary operations on simple feature geometry sets

Description

Geometric unary operations on simple feature geometries. These are all generics, with methods for sfg, sfc and sf objects, returning an object of the same class. All operations work on a per-feature basis, ignoring all other features.

Usage

st_buffer(
  x,
  dist,
  nQuadSegs = 30,
  endCapStyle = "ROUND",
  joinStyle = "ROUND",
  mitreLimit = 1,
  singleSide = FALSE
)
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_reverse(x)
st_node(x)
st_segmentize(x, dfMaxLength, ...)

Arguments

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

endCapStyle

character; style of line ends, one of 'ROUND', 'FLAT', 'SQUARE'

joinStyle

character; style of line joins, one of 'ROUND', 'MITRE', 'BEVEL'

mitreLimit

numeric; limit of extension for a join if joinStyle 'MITRE' is used (default 1.0, minimum 0.0)

singleSide

logical; if TRUE, single-sided buffers are returned for linear geometries, in which case negative dist values give buffers on the right-hand side, positive on the left.

preserveTopology

logical; carry out topology preserving simplification? May be specified for each, or for all feature geometries. Note that topology is preserved only for single feature geometries, not for sets of them.

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 rad or degree; segmentation in the long/lat case takes place along the great circle, using st_geod_segmentize.

Value

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

Details

st_buffer computes a buffer around this geometry/each geometry. If any of endCapStyle, joinStyle, or mitreLimit are set to non-default values ('ROUND', 'ROUND', 1.0 respectively) then the underlying 'buffer with style' GEOS function is used. See postgis.net/docs/ST_Buffer.html for details.

st_boundary returns the boundary of a geometry

st_convex_hull creates the convex hull of a set of points

st_simplify simplifies lines by removing vertices

st_triangulate triangulates set of points (not constrained). st_triangulate requires GEOS version 3.4 or above

st_voronoi creates voronoi tesselation. st_voronoi requires GEOS version 3.5 or above

st_polygonize creates polygon from lines that form a closed ring. In case of st_polygonize, x must be an object of class LINESTRING or MULTILINESTRING, or an sfc geometry list-column object containing these

st_line_merge merges lines. In case of st_line_merge, x must be an object of class MULTILINESTRING, or an sfc geometry list-column object containing these

st_centroid gives the centroid of a geometry

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

st_reverse reverses the nodes in a line

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

st_segmentize adds points to straight lines

Examples

Run this code

# NOT RUN {
## st_buffer, style options (taken from rgeos gBuffer)
l1 = st_as_sfc("LINESTRING(0 0,1 5,4 5,5 2,8 2,9 4,4 6.5)")
op = par(mfrow=c(2,3))
plot(st_buffer(l1, dist = 1, endCapStyle="ROUND"), reset = FALSE, main = "endCapStyle: ROUND")
plot(l1,col='blue',add=TRUE)
plot(st_buffer(l1, dist = 1, endCapStyle="FLAT"), reset = FALSE, main = "endCapStyle: FLAT")
plot(l1,col='blue',add=TRUE)
plot(st_buffer(l1, dist = 1, endCapStyle="SQUARE"), reset = FALSE, main = "endCapStyle: SQUARE")
plot(l1,col='blue',add=TRUE)
plot(st_buffer(l1, dist = 1, nQuadSegs=1), reset = FALSE, main = "nQuadSegs: 1")
plot(l1,col='blue',add=TRUE)
plot(st_buffer(l1, dist = 1, nQuadSegs=2), reset = FALSE, main = "nQuadSegs: 2")
plot(l1,col='blue',add=TRUE)
plot(st_buffer(l1, dist = 1, nQuadSegs= 5), reset = FALSE, main = "nQuadSegs: 5")
plot(l1,col='blue',add=TRUE)
par(op)


l2 = st_as_sfc("LINESTRING(0 0,1 5,3 2)")
op = par(mfrow = c(2, 3))
plot(st_buffer(l2, dist = 1, joinStyle="ROUND"), reset = FALSE, main = "joinStyle: ROUND")
plot(l2, col = 'blue', add = TRUE)
plot(st_buffer(l2, dist = 1, joinStyle="MITRE"), reset = FALSE, main = "joinStyle: MITRE")
plot(l2, col= 'blue', add = TRUE)
plot(st_buffer(l2, dist = 1, joinStyle="BEVEL"), reset = FALSE, main = "joinStyle: BEVEL")
plot(l2, col= 'blue', add=TRUE)
plot(st_buffer(l2, dist = 1, joinStyle="MITRE" , mitreLimit=0.5), reset = FALSE,
   main = "mitreLimit: 0.5")
plot(l2, col = 'blue', add = TRUE)
plot(st_buffer(l2, dist = 1, joinStyle="MITRE",mitreLimit=1), reset = FALSE,
   main = "mitreLimit: 1")
plot(l2, col = 'blue', add = TRUE)
plot(st_buffer(l2, dist = 1, joinStyle="MITRE",mitreLimit=3), reset = FALSE,
   main = "mitreLimit: 3")
plot(l2, col = 'blue', add = TRUE)
par(op)
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)
 # matching Voronoi polygons to data points:
 # https://github.com/r-spatial/sf/issues/1030
 # generate 50 random unif points:
 n = 100
 pts = st_as_sf(data.frame(matrix(runif(n), , 2), id = 1:(n/2)), coords = c("X1", "X2"))
 # compute Voronoi polygons:
 pols = st_collection_extract(st_voronoi(do.call(c, st_geometry(pts))))
 # match them to points:
 pts$pols = pols[unlist(st_intersects(pts, pols))]
 plot(pts["id"], pch = 16) # ID is color
 plot(st_set_geometry(pts, "pols")["id"], xlim = c(0,1), ylim = c(0,1), reset = FALSE)
 plot(st_geometry(pts), add = TRUE)
}
mls = st_multilinestring(list(matrix(c(0,0,0,1,1,1,0,0),,2,byrow=TRUE)))
st_polygonize(st_sfc(mls))
mls = st_multilinestring(list(rbind(c(0,0), c(1,1)), rbind(c(2,0), c(1,1))))
st_line_merge(st_sfc(mls))
plot(nc, axes = TRUE)
plot(st_centroid(nc), add = TRUE, pch = 3)
mp = st_combine(st_buffer(st_sfc(lapply(1:3, function(x) st_point(c(x,x)))), 0.2 * 1:3))
plot(mp)
plot(st_centroid(mp), add = TRUE, col = 'red') # centroid of combined geometry
plot(st_centroid(mp, of_largest_polygon = TRUE), add = TRUE, col = 'blue', pch = 3)
plot(nc, axes = TRUE)
plot(st_point_on_surface(nc), add = TRUE, pch = 3)
if (sf_extSoftVersion()["GEOS"] >= "3.7.0") {
  st_reverse(st_linestring(rbind(c(1,1), c(2,2), c(3,3))))
}
(l = st_linestring(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0))))
st_polygonize(st_node(l))
st_node(st_multilinestring(list(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0)))))
sf = st_sf(a=1, geom=st_sfc(st_linestring(rbind(c(0,0),c(1,1)))), crs = 4326)
seg = st_segmentize(sf, units::set_units(100, km))
seg = st_segmentize(sf, units::set_units(0.01, rad))
nrow(seg$geom[[1]])
# }

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