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#' @inheritParams coord_cartesian
#' @export
#' @rdname coord_map
coord_quickmap <- function(xlim = NULL, ylim = NULL, expand = TRUE, clip = "on") {
ggproto(NULL, CoordQuickmap,
limits = list(x = xlim, y = ylim),
expand = expand,
clip = clip
)
}
#' @rdname ggplot2-ggproto
#' @format NULL
#' @usage NULL
#' @export
CoordQuickmap <- ggproto("CoordQuickmap", CoordCartesian,
aspect = function(ranges) {
# compute coordinates of center point of map
x.center <- sum(ranges$x.range) / 2
y.center <- sum(ranges$y.range) / 2
# compute distance corresponding to 1 degree in either direction
# from the center
x.dist <- dist_central_angle(x.center + c(-0.5, 0.5), rep(y.center, 2))
y.dist <- dist_central_angle(rep(x.center, 2), y.center + c(-0.5, 0.5))
# NB: this makes the projection correct in the center of the plot and
# increasingly less correct towards the edges. For regions of reasonnable
# size, this seems to give better results than computing this ratio from
# the total lat and lon span.
# scale the plot with this aspect ratio
ratio <- y.dist / x.dist
diff(ranges$y.range) / diff(ranges$x.range) * ratio
}
)
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