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_concave_hull(x, ratio, ..., allow_holes)
st_simplify(x, preserveTopology, dTolerance = 0)
st_triangulate(x, dTolerance = 0, bOnlyEdges = FALSE)
st_triangulate_constrained(x)
st_inscribed_circle(x, dTolerance, ...)
st_minimum_rotated_rectangle(x, ...)
st_voronoi(x, envelope, dTolerance = 0, bOnlyEdges = FALSE)
st_polygonize(x)
st_line_merge(x, ..., directed = FALSE)
st_centroid(x, ..., of_largest_polygon = FALSE)
st_point_on_surface(x)
st_reverse(x)
st_node(x)
st_segmentize(x, dfMaxLength, ...)
st_exterior_ring(x, ...)

Value

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

Arguments

x: object of class sfg, sfc or sf
dist: numeric or object of class units; buffer distance for all, or for each of the elements in x. In case x has geodetic coordinates (lon/lat) and sf_use_s2() is TRUE, a numeric dist is taken as distance in meters and a units object in dist is converted to meters. In case x has geodetic coordinates (lon/lat) and sf_use_s2() is FALSE, a numeric dist is taken as degrees, and a units object in dist is converted to arc_degree (and warnings are issued). In case x does not have geodetic coordinates (projected) then numeric dist is assumed to have the units of the coordinates, and a units dist is converted to those if st_crs(x) is not NA.
nQuadSegs: integer; number of segments per quadrant (fourth of a circle), for all or per-feature; see details
endCapStyle: character; style of line ends, one of 'ROUND', 'FLAT', 'SQUARE'; see details
joinStyle: character; style of line joins, one of 'ROUND', 'MITRE', 'BEVEL'; see details
mitreLimit: numeric; limit of extension for a join if joinStyle 'MITRE' is used (default 1.0, minimum 0.0); see details
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; see details
...: ignored
ratio: numeric; fraction convex: 1 returns the convex hulls, 0 maximally concave hulls
allow_holes: logical; if TRUE, the resulting concave hull may have holes
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. If not specified (i.e. the default), then it is internally set equal to FALSE when the input data is specified with projected coordinates or sf_use_s2() returns FALSE. Ignored in all the other cases (with a warning when set equal to FALSE) since the function implicitly calls s2::s2_simplify which always preserve topological relationships (per single feature).
dTolerance: numeric; tolerance parameter, specified for all or for each feature geometry. If you run st_simplify, the input data is specified with long-lat coordinates and sf_use_s2() returns TRUE, then the value of dTolerance must be specified in meters.
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
directed: logical; if TRUE, lines with opposite directions will not be merged
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.

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. If a negative buffer returns empty polygons instead of shrinking, set sf_use_s2() to FALSE See postgis.net/docs/ST_Buffer.html for details.

nQuadSegs, endCapsStyle, joinStyle, mitreLimit and singleSide only work when the GEOS back-end is used: for projected coordinates or when sf_use_s2() is set to FALSE.

st_boundary returns the boundary of a geometry

st_convex_hull creates the convex hull of a set of points

st_concave_hull creates the concave hull of a geometry

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_triangulate_constrained returns the constrained delaunay triangulation of polygons; requires GEOS version 3.10 or above

st_inscribed_circle returns the maximum inscribed circle for polygon geometries. For st_inscribed_circle, if nQuadSegs is 0 a 2-point LINESTRING is returned with the center point and a boundary point of every circle, otherwise a circle (buffer) is returned where nQuadSegs controls the number of points per quadrant to approximate the circle. st_inscribed_circle requires GEOS version 3.9 or above

st_minimum_rotated_rectangle returns the minimum rotated rectangular POLYGON which encloses the input geometry. The rectangle has width equal to the minimum diameter, and a longer length. If the convex hill of the input is degenerate (a line or point) a linestring or point is returned.

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


## 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"))
nc_g = st_geometry(nc)
plot(st_convex_hull(nc_g))
plot(nc_g, border = grey(.5), add = TRUE)
pt = st_combine(st_sfc(st_point(c(0,80)), st_point(c(120,80)), st_point(c(240,80))))
st_convex_hull(pt) # R2
st_convex_hull(st_set_crs(pt, 'OGC:CRS84')) # S2
set.seed(131)
if (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.11.0") > -1) {
 pts = cbind(runif(100), runif(100))
 m = st_multipoint(pts)
 co = sf:::st_concave_hull(m, 0.3)
 coh = sf:::st_concave_hull(m, 0.3, allow_holes = TRUE)
 plot(co, col = 'grey')
 plot(coh, add = TRUE, border = 'red')
 plot(m, add = TRUE)
}

# st_simplify examples:
op = par(mfrow = c(2, 3), mar = rep(0, 4))
plot(nc_g[1])
plot(st_simplify(nc_g[1], dTolerance = 1e3)) # 1000m
plot(st_simplify(nc_g[1], dTolerance = 5e3)) # 5000m
nc_g_planar = st_transform(nc_g, 2264) # planar coordinates, US foot
plot(nc_g_planar[1])
plot(st_simplify(nc_g_planar[1], dTolerance = 1e3)) # 1000 foot
plot(st_simplify(nc_g_planar[1], dTolerance = 5e3)) # 5000 foot
par(op)

if (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.10.0") > -1) {
 pts = rbind(c(0,0), c(1,0), c(1,1), c(.5,.5), c(0,1), c(0,0))
 po = st_polygon(list(pts))
 co = st_triangulate_constrained(po)
 tr = st_triangulate(po)
 plot(po, col = NA, border = 'grey', lwd = 15)
 plot(tr, border = 'green', col = NA, lwd = 5, add = TRUE)
 plot(co, border = 'red', col = 'NA', add = TRUE)
}
if (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.9.0") > -1) {
  nc_t = st_transform(nc, 'EPSG:2264')
  x = st_inscribed_circle(st_geometry(nc_t))
  plot(st_geometry(nc_t), asp = 1, col = grey(.9))
  plot(x, add = TRUE, col = '#ff9999')
}
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 (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.5.0") > -1) {
 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$pols = pols[unlist(st_intersects(pts, pols))]
 plot(pts["id"], pch = 16) # ID is color
 plot(st_set_geometry(pts, "pols")["id"], xlim = c(0,1), ylim = c(0,1), reset = FALSE)
 plot(st_geometry(pts), add = TRUE)
 layout(matrix(1)) # reset plot layout
}
mls = st_multilinestring(list(matrix(c(0,0,0,1,1,1,0,0),,2,byrow=TRUE)))
st_polygonize(st_sfc(mls))
mls = st_multilinestring(list(rbind(c(0,0), c(1,1)), rbind(c(2,0), c(1,1))))
st_line_merge(st_sfc(mls))
plot(nc_g, axes = TRUE)
plot(st_centroid(nc_g), add = TRUE, pch = 3, col = 'red')
mp = st_combine(st_buffer(st_sfc(lapply(1:3, function(x) st_point(c(x,x)))), 0.2 * 1:3))
plot(mp)
plot(st_centroid(mp), add = TRUE, col = 'red') # centroid of combined geometry
plot(st_centroid(mp, of_largest_polygon = TRUE), add = TRUE, col = 'blue', pch = 3)
plot(nc_g, axes = TRUE)
plot(st_point_on_surface(nc_g), add = TRUE, pch = 3, col = 'red')
if (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.7.0") > -1) {
  st_reverse(st_linestring(rbind(c(1,1), c(2,2), c(3,3))))
}
(l = st_linestring(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0))))
st_polygonize(st_node(l))
st_node(st_multilinestring(list(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0)))))
sf = st_sf(a=1, geom=st_sfc(st_linestring(rbind(c(0,0),c(1,1)))), crs = 4326)
if (require(lwgeom, quietly = TRUE)) {
 seg = st_segmentize(sf, units::set_units(100, km))
 seg = st_segmentize(sf, units::set_units(0.01, rad))
 nrow(seg$geom[[1]])
}