R/bb2bbox.R

In KimByoungmo/modefiedggmap: Spatial Visualization with ggplot2

#' Convert a bb specification to a bbox specification
#'
#' In ggmap, all maps (class ggmap) have the bb attribute, a data
#' frame bounding box specification in terms of the bottom left and
#' top right points of the spatial extent. This function converts
#' this specification to a named double vector (with names left,
#' bottom, right, top) specification that is used in some querying
#' functions (e.g. get_stamenmap).
#'
#' @param bb a bounding box in bb format (see examples)
#' @return a bounding box in bbox format (see examples)
#' @author David Kahle \email{david.kahle@@gmail.com}
#' @export
#' @examples
#'
#' \dontrun{ cut down on R CMD check time
#'
#' # grab a center/zoom map and compute its bounding box
#' gc <- geocode("white house, washington dc")
#' map <- get_map(gc)
#' (bb <- attr(map, "bb"))
#' (bbox <- bb2bbox(bb))
#'
#' # use the bounding box to get a stamen map
#' stamMap <- get_stamenmap(bbox)
#'
#' ggmap(map) +
#'   geom_point(
#'     aes(x = lon, y = lat),
#'     data = gc, colour = "red", size = 3
#'   )
#'
#' ggmap(stamMap) +
#'   geom_point(
#'     aes(x = lon, y = lat),
#'     data = gc, colour = "red", size = 3
#'   )
#'
#'
#' }
#'
#'
bb2bbox <- function(bb){
  with(bb,
    c(
      left = ll.lon, bottom = ll.lat,
      right = ur.lon, top = ur.lat
    )
  )
}