Convert an sf, numeric, or other object to a POINT (sfg) or POINT, MULTIPOINT, LINESTRING, or MULTILINESTRING (sfc) object

Works with sf, sfc, and bbox objects using sf::st_centroid(). Works with sf_bbox_point()

Usage

as_point(..., to = "POINT")

as_points(..., to = "POINT", call = caller_env())

as_startpoint(x)

as_endpoint(x)

as_line(..., to = "LINESTRING", call = caller_env())

as_lines(..., to = "LINESTRING")

as_polygons(..., to = "POLYGON")

as_centroid(x, ...)

Arguments

...: See details.
to: The geometry type to return, either POINT or MULTIPOINT or LINESTRING or MULTILINESTRING.
call: The execution environment of a currently running function, e.g. caller_env(). The function will be mentioned in error messages as the source of the error. See the call argument of abort() for more information.
x: A sf, sfc, or bbox object.

Details

Using as_point:

as_point() always returns a single point sfg object. The ... parameter is passed to sf::st_centroid() if ... is a sf, sfc, or bbox object, sf_bbox_point() includes a bbox object and a string indicating the requested point position, or sf::st_point() if ... includes a numeric vector.

Using as_points:

as_points() always returns an sfc object. The parameters are passed to as_point using purrr::map() and then converted to sfc using sf::st_as_sfc(). The ... parameters must include a crs, otherwise the crs will be NA for the resulting sfc object.

Using as_startpoint and as_endpoint:

as_startpoint() and as_endpoint() require a LINESTRING OR MULTILINESTRING geometry type sf or sfc object that is passed to lwgeom::st_startpoint() or lwgeom::st_endpoint() respectively. Both functions always return a sfc object matching the CRS of the input geometry.

Using as_lines:

If params do not have POINT or MULTIPOINT geometry, they are passed to as_points() to convert to an sfc object. If the parameters have POINT geometry, they are combined to create a MULTIPOINT geometry.

For as_lines() the ... parameters are passed to as_points() and/or sf::st_cast().

Both as_line and as_lines do not consistently retain the coordinate reference system of the original object but this should be improved in the future.

Using as_centroid()

as_centroid() always returns a sfc object with the same length and crs as the input object.

Examples

nc <- sf::read_sf(system.file("shape/nc.shp", package = "sf"))

as_point(nc)
#> POINT (-79.40065 35.55937)

as_point(c("xmax", "ymax"), bbox = as_bbox(nc))
#> POINT (-75.45698 36.58965)

as_points(nc)
#> Geometry set for 1 feature 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -79.40065 ymin: 35.55937 xmax: -79.40065 ymax: 35.55937
#> Geodetic CRS:  NAD27
#> POINT (-79.40065 35.55937)

as_points(nc[1, ], nc[2, ])
#> Geometry set for 2 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -81.49823 ymin: 36.4314 xmax: -81.12513 ymax: 36.49111
#> Geodetic CRS:  NAD27
#> POINT (-81.49823 36.4314)
#> POINT (-81.12513 36.49111)

nc_line <- as_line(c(as_points(nc[1, ]), as_points(nc[10, ])))

as_startpoint(nc_line)
#> Linking to GEOS 3.10.2, GDAL 3.4.1, PROJ 8.2.1; sf_use_s2() is TRUE
#> Geometry set for 1 feature 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -81.49823 ymin: 36.4314 xmax: -81.49823 ymax: 36.4314
#> Geodetic CRS:  NAD27
#> POINT (-81.49823 36.4314)

as_endpoint(nc_line)
#> Geometry set for 1 feature 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -80.23429 ymin: 36.40042 xmax: -80.23429 ymax: 36.40042
#> Geodetic CRS:  NAD27
#> POINT (-80.23429 36.40042)

as_centroid(nc)
#> Geometry set for 100 features 
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: -84.05986 ymin: 34.07671 xmax: -75.8095 ymax: 36.49111
#> Geodetic CRS:  NAD27
#> First 5 geometries:
#> POINT (-81.49823 36.4314)
#> POINT (-81.12513 36.49111)
#> POINT (-80.68573 36.41252)
#> POINT (-76.02719 36.40714)
#> POINT (-77.41046 36.42236)