Geometric unary operations on simple feature geometry sets
Source:R/geom-transformers.R
geos_unary.Rd
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, ...)
Arguments
- x
object of class
sfg
,sfc
orsf
- dist
numeric or object of class
units
; buffer distance for all, or for each of the elements inx
. In casex
has geodetic coordinates (lon/lat) andsf_use_s2()
isTRUE
, a numericdist
is taken as distance in meters and aunits
object indist
is converted to meters. In casex
has geodetic coordinates (lon/lat) andsf_use_s2()
isFALSE
, a numericdist
is taken as degrees, and aunits
object indist
is converted toarc_degree
(and warnings are issued). In casex
does not have geodetic coordinates (projected) then numericdist
is assumed to have the units of the coordinates, and aunits
dist
is converted to those ifst_crs(x)
is notNA
.- 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 negativedist
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 orsf_use_s2()
returnsFALSE
. Ignored in all the other cases (with a warning when set equal toFALSE
) since the function implicitly callss2::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 andsf_use_s2()
returnsTRUE
, then the value ofdTolerance
must be specified in meters.- bOnlyEdges
logical; if TRUE, return lines, else return polygons
- envelope
object of class
sfc
orsfg
containing aPOLYGON
with the envelope for a voronoi diagram; this only takes effect when it is larger than the default envelope, chosen whenenvelope
is an empty polygon- directed
logical; if
TRUE
, lines with opposite directions will not be merged- of_largest_polygon
logical; for
st_centroid
: ifTRUE
, return centroid of the largest (sub)polygon of aMULTIPOLYGON
rather than of the wholeMULTIPOLYGON
- 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 classunits
with length unitsrad
ordegree
; 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
See also
chull for a more efficient algorithm for calculating the convex hull
Examples
## 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"))
#> Reading layer `nc' from data source
#> `/home/runner/work/_temp/Library/sf/shape/nc.shp' using driver `ESRI Shapefile'
#> Simple feature collection with 100 features and 14 fields
#> Geometry type: MULTIPOLYGON
#> Dimension: XY
#> Bounding box: xmin: -84.32385 ymin: 33.88199 xmax: -75.45698 ymax: 36.58965
#> Geodetic CRS: NAD27
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
#> Geometry set for 1 feature
#> Geometry type: LINESTRING
#> Dimension: XY
#> Bounding box: xmin: 0 ymin: 80 xmax: 240 ymax: 80
#> CRS: NA
#> LINESTRING (0 80, 240 80)
st_convex_hull(st_set_crs(pt, 'OGC:CRS84')) # S2
#> Geometry set for 1 feature
#> Geometry type: POLYGON
#> Dimension: XY
#> Bounding box: xmin: -120 ymin: 80 xmax: 120 ymax: 80
#> Geodetic CRS: WGS 84
#> POLYGON ((-120 80, 0 80, 120 80, -120 80))
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))
#> Geometry set for 1 feature
#> Geometry type: GEOMETRYCOLLECTION
#> Dimension: XY
#> Bounding box: xmin: 0 ymin: 0 xmax: 1 ymax: 1
#> CRS: NA
#> GEOMETRYCOLLECTION (POLYGON ((0 0, 0 1, 1 1, 0 ...
mls = st_multilinestring(list(rbind(c(0,0), c(1,1)), rbind(c(2,0), c(1,1))))
st_line_merge(st_sfc(mls))
#> Geometry set for 1 feature
#> Geometry type: LINESTRING
#> Dimension: XY
#> Bounding box: xmin: 0 ymin: 0 xmax: 2 ymax: 1
#> CRS: NA
#> LINESTRING (0 0, 1 1, 2 0)
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')
#> Warning: st_point_on_surface may not give correct results for longitude/latitude data
if (compareVersion(sf_extSoftVersion()[["GEOS"]], "3.7.0") > -1) {
st_reverse(st_linestring(rbind(c(1,1), c(2,2), c(3,3))))
}
#> LINESTRING (3 3, 2 2, 1 1)
(l = st_linestring(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0))))
#> LINESTRING (0 0, 1 1, 0 1, 1 0, 0 0)
st_polygonize(st_node(l))
#> GEOMETRYCOLLECTION (POLYGON ((0 0, 0.5 0.5, 1 0, 0 0)), POLYGON ((0.5 0.5, 0 1, 1 1, 0.5 0.5)))
st_node(st_multilinestring(list(rbind(c(0,0), c(1,1), c(0,1), c(1,0), c(0,0)))))
#> MULTILINESTRING ((0 0, 0.5 0.5), (0.5 0.5, 1 1, 0 1, 0.5 0.5), (0.5 0.5, 1 0, 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]])
}
#> Linking to liblwgeom 3.0.0beta1 r16016, GEOS 3.10.2, PROJ 8.2.1
#>
#> Attaching package: ‘lwgeom’
#> The following object is masked from ‘package:sf’:
#>
#> st_perimeter
#> [1] 5