R/concave.R

In lawn: Client for 'Turfjs' for 'Geospatial' Analysis

#' Concave hull polygon
#'
#' Takes a set of [data-Point]'s and returns a concave hull polygon.
#' Internally, this implements a Monotone chain algorithm
#'
#' @export
#' @param points Input points in a [data-FeatureCollection].
#' @param maxEdge The size of an edge necessary for part of the hull to
#' become concave (in miles).
#' @param units	Used for maxEdge distance (miles (default) or kilometers).
#' @template lint
#' @family transformations
#' @return a concave hull [data-Polygon]
#' @examples \dontrun{
#' points <- '{
#'   "type": "FeatureCollection",
#'   "features": [
#'     {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.601226, 44.642643]
#'       }
#'     }, {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.591442, 44.651436]
#'       }
#'     }, {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.580799, 44.648749]
#'       }
#'     }, {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.573589, 44.641788]
#'       }
#'     }, {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.587665, 44.64533]
#'       }
#'     }, {
#'       "type": "Feature",
#'       "properties": {},
#'       "geometry": {
#'         "type": "Point",
#'         "coordinates": [-63.595218, 44.64765]
#'       }
#'     }
#'     ]
#' }'
#' lawn_concave(points, 1)
#'
#' lawn_concave(points) %>% view
#' }
lawn_concave <- function(points, maxEdge = 1, units = "miles", lint = FALSE) {
  points <- convert(points)
  lawnlint(points, lint)
  if (lint) {
    is_type(points, type_top = "FeatureCollection", type_lower = "Point")
  }
  ct$eval(sprintf("var cv = turf.concave(%s, {maxEdge:%s, units:'%s'});",
    points, maxEdge, units))
  structure(ct$get("cv"), class = "linestring")
}