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#' Projected arrows function
#'
#' \code{parrows} takes pairs of coordinates and draws arrows between
#' them, possibly after projection.
#'
#' The \code{\link[mapproj]{mapproject}} function is used for
#' projection.
#'
#' @param x0,y0 coordinates of points from which to draw.
#' @param x1,y1 coordinates of points to which to draw
#' @inheritParams pimage
#' @param ... Additional arguments passed to the
#' \code{\link[graphics]{arrows}}
#' @seealso \code{\link[graphics]{arrows}},
#' \code{\link[mapproj]{mapproject}},
#' \code{\link[autoimage]{pimage}}
#' @return NULL
#' @examples
#' data(narccap)
#' # plot image using bonne projection (w/o grid lines)
#' pimage(lon, lat, tasmax[,,1], proj = "bonne",
#' parameters = 40, paxes.args = list(grid = FALSE))
#' # load some data for larger U.S. cities
#' data(us.cities, package = "maps")
#' cityxy <- list(x = us.cities$long[1:5], y = us.cities$lat[1:5])
#' parrows(cityxy$x[1:4], cityxy$y[1:4], cityxy$x[2:5], cityxy$y[2:5],
#' proj = "bonne", col = "orange")
#' @export
parrows <- function(x0, y0, x1 = x0, y1 = y0, proj, ...) {
arglist <- list(...)
object0 <- arg.check.plines(x0, y0, "b", proj, arglist)
object1 <- arg.check.plines(x1, y1, "b", proj, arglist)
object <- arglist
object$x0 <- object0$x
object$y0 <- object0$y
object$x1 <- object1$x
object$y1 <- object1$y
if (proj != "none") {
projxy0 <- mapproj::mapproject(object0$x, object0$y)
projxy1 <- mapproj::mapproject(object1$x, object1$y)
object$x0 <- projxy0$x
object$y0 <- projxy0$y
object$x1 <- projxy1$x
object$y1 <- projxy1$y
}
f <- graphics::arrows
do.call(f, object)
}
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