Guess extract boundaries — ors

Makes reasonable guesses about the boundaries of the OpenStreetMap extract mounted to the active ORS instance. ors_guess samples points over a specified area and tries to snap these points to the nearest defined street. It is a simple wrapper around ors_snap.

This function can be useful to validate an ORS setup or to find the extract area of a remote (non-official) ORS server.

Usage

ors_guess(
  poly = NULL,
  n = 1000,
  radius = 1000,
  type = "regular",
  poly_fun = sf::st_convex_hull,
  instance = NULL,
  ...
)

Arguments

poly

[various]

An sf/sfc object or any object that can be parsed by st_bbox. If NULL, defaults to global boundaries. Needed to narrow down the area of guessing. For best results, poly should be as small and precise as possible.

n

[integer]

Number of points to sample. More points mean slower but more precise guess work.

radius

[numeric]

Snapping radius. Points are only snapped to a street if the street lies within this distance to the source point.

type

[character]

Spatial sampling type. For details, see st_sample.

poly_fun

[function]

Function to derive a boundary polygon from successfully snapped points. Defaults to st_convex_hull. Other useful functions are st_concave_hull and st_polygonize.

instance

[ors_instance]

Object of an OpenRouteService instance that should be used for route computations. It is recommended to use ors_instance to set an instance globally. This argument should only be used if activating an instance globally is not feasible.

...

Further arguments passed to poly_fun

Value

An sfc polygon that approximately represents the boundaries of the current ORS extract.

Note

ors_guess usually has to make a lot of requests. If you are rate-limited, you are strongly advised against the usage of this function.

Examples

if (FALSE) { # \dontrun{
bounds <- get_extract_boundaries()
bounds <- sf::st_buffer(bounds, 10000)
plot(bounds)

bounds2 <- ors_guess(bounds)
plot(bounds2, add = TRUE)

bounds3 <- ors_guess(bounds, n = 10000)
plot(bounds3, add = TRUE)

bounds4 <- ors_guess(bounds, poly_fun = sf::st_concave_hull, ratio = 0)
plot(bounds4, add = TRUE)} # }