R/get-bbox.R

In osmplotr: Bespoke Images of 'OpenStreetMap' Data

#' get_bbox
#'
#' Converts a string of latitudes and longitudes into a square matrix to be
#' passed as a \code{bbox} argument (to \code{\link{extract_osm_objects}},
#' \code{\link{osm_basemap}}, or \code{\link{make_osm_map}}).
#'
#' @param latlon A vector of (longitude, latitude, longitude, latitude) values.
#' @return A 2-by-2 matrix of 4 elements with columns of min and max values, and
#' rows of x and y values.
#' @export
#'
#' @examples
#' bbox <- get_bbox (c (-0.15, 51.5, -0.1, 51.52))
get_bbox <- function (latlon) {

    if (missing (latlon))
        stop ("latlon must be supplied")
    if (!is.numeric (latlon))
        stop ("latlon is not numeric")
    if (length (latlon) < 4)
        stop ("latlon must have length = 4")
    if (length (latlon) > 4) {

        warning ("latlon has length > 4; only first 4 elements will be used")
        latlon <- latlon [1:4]
    }

    if (latlon [1] > latlon [3]) latlon [c (1, 3)] <- latlon [c (3, 1)]
    if (latlon [2] > latlon [4]) latlon [c (2, 4)] <- latlon [c (4, 2)]

    bbox <- matrix (latlon, nrow = 2, ncol = 2)
    rownames (bbox) <- c ("x", "y")
    bbox <- data.frame (bbox)
    names (bbox) <- c ("min", "max")
    as.matrix (bbox)
}