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Coerce arbitrary geometries to representative points

Source: R/crs-geometry.R
coerce_to_points.Rd

Converts the geometry column of an sf object to POINTs using one of several strategies.

Usage

coerce_to_points(
  x,
  mode = c("auto", "centroid", "point_on_surface", "surface", "line_midpoint",
    "bbox_center"),
  tmp_project = TRUE
)

Arguments

x

An sf object.

mode

One of "auto", "centroid", "point_on_surface", "surface", "line_midpoint", "bbox_center".

tmp_project

Logical; temporarily project for line-based midpoints. When x has no CRS and the lon/lat heuristic of ensure_projected() takes its coordinates for degrees (inside the lon/lat envelope and more than one unit across, or with decimal-degree precision), that temporary projection interprets them as EPSG:4326 (with a warning) and the midpoints returned are geodesic ones brought back to the input's numbers, not planar midpoints. Set the CRS, or pass tmp_project = FALSE, for planar data.

Value

An sf object with geometry coerced to POINTs, row for row with x; an empty input geometry gives an empty POINT.

Details

The result has one row per row of x, in the same order. An EMPTY geometry of any type, lines included, becomes an EMPTY POINT in its own row; prep_model_data() and make_folds() then drop such rows, as they drop any other empty geometry. Empty lines are never handed to sf::st_line_sample(): it yields no midpoint for them, which would misalign the result, and with sf 1.0.x an empty MULTILINESTRING (or an empty part of one) crashed the R session. An empty part inside a non-empty feature is ignored, so the feature gets the point its other parts give; GEOS's interior point, used by "point_on_surface" and by the temporary projection's choice of CRS, segfaulted on an empty line part too.

See also

Other spatial data preparation: clip_target_for(), ensure_projected(), harmonize_crs(), prep_model_data()

Examples

library(sf)
poly <- st_sf(
  id = 1,
  geometry = st_sfc(st_polygon(list(rbind(
    c(0, 0), c(2, 0), c(2, 2), c(0, 2), c(0, 0)
  ))), crs = 32632)
)
coerce_to_points(poly, "auto")  # interior representative point
#> Simple feature collection with 1 feature and 1 field
#> Geometry type: POINT
#> Dimension:     XY
#> Bounding box:  xmin: 1 ymin: 1 xmax: 1 ymax: 1
#> Projected CRS: WGS 84 / UTM zone 32N
#>   id    geometry
#> 1  1 POINT (1 1)