create.boundary.prevR.r

#' Provide national boundaries of a country.
#'
#'
#' This function uses the data set [TMWorldBorders]. One or several countries
#' can be selected and will be returned as an object of class
#' [sp::SpatialPolygons-class].
#'
#' @param countries a vector of character string corresponding to the name of
#' the countries you want to extract from the dataset. If \code{NULL},
#' a dialogue box will be appear in order to select the desired country.
#' @param multiple should the dialog box allow multiple selection
#' (unused if \code{countries} is specified)?
#' @param proj projection of clusters coordinates used in \code{data}
#'   (longitude and latitude in decimal degrees by default). One of
#'   (i) character: a string accepted by GDAL, (ii) integer, a valid EPSG value
#'   (numeric), or (iii) an object of class `crs`, see [sf::st_crs()].
#'
#' @return Object of class [sp::SpatialPolygons-class].
#'
#' @note The result will be automatically plotted.
#'
#' @seealso [TMWorldBorders].
#'
#' @examples
#' \dontrun{
#' boundary <- create.boundary()
#' }
#' \dontshow{
#' par(ask = TRUE)
#' }
#' boundary <- create.boundary("Burkina Faso")
#' boundary <- create.boundary("Burkina Faso",
#'   proj = "+proj=utm +zone=30 +ellps=WGS84 +datum=WGS84 +units=m +no_defs"
#' )
#' boundary <- create.boundary(countries = c("Burkina Faso", "Ghana", "Benin"))
#' \dontshow{
#' par(ask = FALSE)
#' }
#'
#' @export
#' @keywords manip spatial

create.boundary <- function(
    countries = NULL,
    multiple = FALSE,
    proj = "+proj=longlat +datum=WGS84"
  ) {
  if (is.null(countries)) {
    title <- c(
      gettext("Select one country:", domain = "R-prevR"),
      gettext("Select countries (use CTRL):", domain = "R-prevR")
    )[c(!multiple, multiple)]
    countries <- select.list(
      sort(TMWorldBorders$NAME),
      multiple = multiple,
      title = title
    )
  }
  if (length(countries) == 0) {
    return(NULL)
  }
  ind <- match(countries, as.character(TMWorldBorders$NAME), nomatch = 0)
  if (any(ind == 0)) {
    invalid.names <- paste(countries[ind == 0], collapse = ", ")
    n.invalid <- length(countries[ind == 0])
    stop.mess <- sprintf(
      ngettext(
        n.invalid,
        "%s is not a valid country name.",
        "%s are not valid country names.",
        domain = "R-prevR"
      ),
      invalid.names
    )
    stop(stop.mess, call. = FALSE)
  }

  boundary <- TMWorldBorders[ind, ]
  if (!is.null(proj)) {
    boundary <- sf::st_transform(boundary, proj)
  }
  plot(boundary["NAME"], axes = TRUE)
  if (length(countries) == 1) title(main = countries)
  message(
    paste0(
      "Source: World Borders Dataset 0.3 (2008)\nProvided by Bjorn Sandvik, ",
      "The dataset was derived by Schuyler Erle from public domain sources.\n",
      "Sean Gilles did some clean up and made some enhancements.\n",
      "The dataset is available under a Creative Commons Attribution-Share ",
      "Alike License.\n",
      "https://creativecommons.org/licenses/by-sa/3.0/\n",
      "The boundaries, names designations used do not imply official ",
      "endorsement or acceptance by the authors."
    ),
    domain = "R-prevR"
  )
  boundary
}