Compute donut polygons

donut_polygons() turns tidy category values at spatial locations into an sf polygon layer. Each row of data represents one category for one location.

Usage

donut_polygons(
  data,
  id,
  category,
  value,
  lon = NULL,
  lat = NULL,
  input_crs = 4326,
  crs = NULL,
  map = NULL,
  radius_range = NULL,
  inner_radius = 0.55,
  n = 96,
  start_angle = pi/2
)

Arguments

data

A data frame or sf object. If data is not an sf object, lon and lat must be supplied.

id

Unquoted column identifying each donut location.

category

Unquoted column identifying donut categories.

value

Unquoted numeric column giving non-negative category values.

lon, lat

Unquoted longitude and latitude columns. Required when data is not an sf object.

input_crs

Coordinate reference system for lon and lat, or for an sf object with missing CRS. Defaults to EPSG:4326.

crs

Target projected CRS used to build the donut polygons. If NULL, a projected CRS is chosen from map, data, or an estimated UTM zone.

map

Optional sf object used only to choose the working CRS and default donut radius range.

radius_range

Numeric vector of length 2 giving minimum and maximum donut radii in map units. If NULL, a range is derived from the map extent.

inner_radius

Numeric value in (0, 1) giving the inner radius as a proportion of the outer radius.

n

Number of points used to approximate a complete outer circle.

start_angle

Start angle in radians. The default starts at 12 o'clock.

Value

An sf object with one polygon per non-zero location-category pair.

Examples

demo <- data.frame(
  place = rep(c("A", "B"), each = 3),
  lon = rep(c(-71.3, -71.1), each = 3),
  lat = rep(c(46.75, 46.85), each = 3),
  category = rep(c("x", "y", "z"), times = 2),
  value = c(10, 20, 5, 5, 15, 10)
)

donuts <- donut_polygons(demo, place, category, value, lon = lon, lat = lat)
plot(donuts["category"])