R/ggpolar.R
In EarthSystemDiagnostics/grfxtools: An R package of tools to assist with various plotting tasks
Defines functions
ggpolar
Documented in
ggpolar
#' Nicely formatted polar ggplot
#'
#' Produce nicely formatted maps of the Arctic or Antarctic in polar
#' projection. Also works for longitudinal segments, e.g. just Greenland.
#'
#' @param pole character; which pole: north ("N") or south ("S")? Note that
#' full-longitude south polar plots only include the Antarctic main land,
#' irrespective of the latitude setting.
#' @param data.layer optional ggplot2 layer of data onto which the polar map
#' shall be plotted. Defaults to \code{NULL} which only plots the map.
#' @param max.lat maximum latitude in degree.
#' @param min.lat minimum latitude in degree.
#' @param max.lon maximum longitude in degree.
#' @param min.lon minimum longitude in degree.
#' @param longitude.spacing interval between longitude axis tick marks.
#' @param n.lat.labels approximate number of latitude tick marks.
#' @param plot.political.boundaries logical; should political (country)
#' boundaries be plotted? Defaults to FALSE.
#' @param land.fill.colour colour to shade the land (default "Grey").
#' @param land.outline.colour colour for the land surface outlines (default
#' "Black"); set to the same colour as \code{land.fill.colour} to hide
#' them. This parameter also controls the colours of the political boundaries,
#' if they are switched on.
#' @param rotate logical; if plotting a segment of < 360 degrees longitude,
#' rotate the plot so that north is up (or south is down) as seen from the
#' mean longitude of the segment.
#' @param nearest.x.degrees round latitude tickmarks to how many degrees?
#' @param lat.ax.vals manually set the latitude axis values where to plot
#' latitude labels and lines. This overrides the automatic setting by
#' \code{n.lat.labels} and \code{x.nearest.degress}, while the default
#' \code{NULL} means to use the automatic setting.
#' @param long.ax.vals manually set the longitude axis values where to plot
#' longitude labels and lines. This overrides the automatic setting by
#' \code{longitude.spacing}, while the default \code{NULL} means to use the
#' automatic setting.
#' @param plt.lat.axes logical; shall latitude axes be plotted?
#' @param plt.lat.labels logical; shall latitude labels be plotted? Per default
#' set to the value of \code{plt.lat.axes}.
#' @param plt.lon.axes logical; shall longitude axes be plotted?
#' @param plt.lon.labels logical; shall longitude labels be plotted? Per default
#' set to the value of \code{plt.lon.axes}.
#' @param f.long.label.ticks fraction of the plotted latitude axis range by
#' which the longitude ticksmarks extend behind the outer latitude axis,
#' i.e. the minimum (maximum) latitude for north (south) polar plots.
#' @param f.long.label.pos fraction of the plotted latitude axis range by
#' which the longitude labels are offset from the outer latitude axis.
#' @param rotate.long.labels logical; controls whether the longitude axis labels
#' are rotated according to their value and the setting of \code{rotate} (the
#' default) or not.
#' @param lat.ax.labs.pos longitudinal positions of the latitude axis
#' labels. Per default, the labels are placed at 0 E (180 W) for north (south)
#' polar plots or at the mean longitude of a segment; use this parameter to
#' override the default setting.
#' @param ax.labs.size size in mm of latitude and longitude axis labels.
#' @param size size in mm of the continental and land outlines.
#' @param size.axes size in mm of the latitude and longitude axes.
#' @param size.outer size in mm of the outer (and potential inner) longitude
#' circle and, if plotting a segment, of the outer latitude lines.
#' @param clip Should drawing be clipped to the extent of the plot panel? A
#' setting of \code{"on"} (the default) means yes, and a setting of
#' \code{"off"} means no. For details, please see
#' \code{\link[ggplot2]{coord_cartesian}}.
#' @importFrom rlang .data
#' @author Andrew Dolman <andrew.dolman@awi.de> with some modifications by
#' Thomas Münch.
#' @source Code adapted from Mikey Harper's plot; see
#' https://stackoverflow.com/a/49084793.
#'
#' Coastlines and political boundaries for complete north polar plots, and for
#' north and south polar segment plots, have been obtained from the
#' rnaturalearth package:
#' https://cran.r-project.org/web/packages/rnaturalearth/index.html
#'
#' Complete south polar plots use ggplot2 data.
#' @examples
#'
#' # full north polar plot
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4)
#'
#' # with political boundaries
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
#' plot.political.boundaries = TRUE)
#'
#' # hide land surface outlines
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
#' land.outline.colour = "Grey")
#'
#' # full south polar plot
#' ggpolar(pole = "S", max.lat = -60, min.lat = -90)
#'
#' # north polar segment plot with adjusted longitude and latitude labelling
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55,
#' max.lon = 0, min.lon = -80,
#' longitude.spacing = 15, n.lat.labels = 5)
#'
#' # rotate the segment
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55,
#' max.lon = 0, min.lon = -80,
#' longitude.spacing = 15, n.lat.labels = 5,
#' rotate = TRUE)
#'
#' # south polar segment plot
#' ggpolar(pole = "S", max.lat = -55, min.lat = -90,
#' max.lon = 80, min.lon = -20,
#' longitude.spacing = 30, rotate = TRUE)
#'
#' # it is also possible to plot a ring segment;
#' # additionally, there are various options to cuzstomize position and look of
#' # axis labels etc., with a few examples shown here
#' ggpolar(pole = "N", max.lat = 85, min.lat = 57.5,
#' max.lon = -10, min.lon = -75, rotate = TRUE,
#' lat.ax.vals = c(60, 70, 80), # explicitly specify latitude labels
#' long.ax.vals = -c(20, 40, 60), # explicitly specify longitude labels
#' f.long.label.ticks = Inf, # don't draw longitude lines beyond segment
#' f.long.label.pos = 15, # adjust label position from segment outline
#' rotate.long.labels = FALSE, # don't rotate longitude labels
#' lat.ax.labs.pos = -75 - c(3.5, 5, 10), # move latitude labels to left side
#' ax.labs.size = 4.75) # larger labels
#'
#' # ---------------------------------------------------------------------------
#'
#' # if you want to add points or a spatial field of data to a ggpolar plot, it
#' # can be convenient to create that plot separately and then provide it as an
#' # argument to ggpolar, so that it can be added to the polar plot internally:
#'
#' library(ggplot2)
#'
#' # create some dummy data
#' nx <- 360 / 5
#' ny <- 30 / 5
#'
#' lon <- seq(0, 355, length.out = nx)
#' lat <- seq(-65, -90, length.out = ny)
#'
#' df <- data.frame(lon = rep(lon, times = ny), lat = rep(lat, each = nx),
#' dat = runif(n = nx * ny, min = -1, max = 1))
#'
#' # Colorbrewer2 colour scales for plotting the "correlation" data can be
#' # obtained directly with the respective grfxtools function
#' colour.scale <- ColorPal("RdBu", rev = TRUE)
#'
#' # create ggplot for data
#' p <- ggplot() +
#' geom_tile(aes(x = lon, y = lat, fill = dat),
#' data = df, colour = "transparent") +
#' scale_fill_gradientn(colours = colour.scale,
#' limits = c(-1, 1),
#' name = "Correlation") +
#' theme(legend.key.height = unit(0.75, units = "inches"),
#' legend.text = element_text(size = 18),
#' legend.title = element_text(size = 18),
#' text = element_text(size = 18))
#'
#' # plot data projected on south polar map
#' ggpolar(pole = "S", data.layer = p,
#' max.lat = -60, min.lat = -90, n.lat.labels = 3,
#' longitude.spacing = 45,
#' land.fill.colour = "transparent")
#'
#' # ---------------------------------------------------------------------------
#'
#' \dontrun{
#' ggpolar(pole = "W", max.lat = -55, min.lat = -90)
#' ggpolar(pole = "S", max.lat = 90, min.lat = 55)
#' ggpolar(pole = "S", max.lat = -90, min.lat = -55)
#' }
#' @export
ggpolar <- function(pole = c("N", "S"), data.layer = NULL, max.lat, min.lat,
max.lon = 180, min.lon = -180, longitude.spacing = 60,
n.lat.labels = 4, plot.political.boundaries = FALSE,
land.fill.colour = "Grey", land.outline.colour = "Black",
rotate = FALSE, nearest.x.degrees = 5,
lat.ax.vals = NULL, long.ax.vals = NULL,
plt.lat.axes = TRUE, plt.lat.labels = plt.lat.axes,
plt.lon.axes = TRUE, plt.lon.labels = plt.lon.axes,
f.long.label.ticks = 20, f.long.label.pos = 7,
rotate.long.labels = TRUE, lat.ax.labs.pos = NULL,
ax.labs.size = 4, size = 0.5, size.axes = 0.25,
size.outer = 1, clip = "on") {
pole <- match.arg(pole, choices = c("N", "S"))
if (pole == "N" & max.lat < 0) stop("If pole == N, max.lat should be positive")
if (pole == "S" & min.lat > 0) stop("If pole == S, min.lat should be negative")
# degree symbol
degree.sym <- "\u00b0"
stopifnot(max.lat > min.lat)
stopifnot(max.lon <= 180 & min.lon >= -180 & max.lat <= 90 & min.lat >= -90)
is.segment <- (min.lon == -180 & max.lon == 180) == FALSE
mean.lon <- mean(c(min.lon, max.lon))
# if not a segment
if (!is.segment) {
mean.lon <- ifelse(pole == "N", 0, 180)
}
rotate.to <- 0
if (rotate & is.segment) {rotate.to <- mean.lon}
lat.range <- abs(max.lat - min.lat)
d.lat.ax.vals <- nearest.x.degrees *
round((max.lat - min.lat)/n.lat.labels/nearest.x.degrees)
# Hemisphere specific values
if (pole == "N") {
if (!length(lat.ax.vals)) {
lat.ax.vals <- seq(min.lat + d.lat.ax.vals, max.lat, by = d.lat.ax.vals)
}
outer.lat.ax.val <- min.lat
inner.lat.ax.val <- ifelse(max.lat == 90, NA, max.lat)
long.lab.pos.1 <- outer.lat.ax.val - (lat.range / f.long.label.ticks)
long.lab.pos.2 <- outer.lat.ax.val - (lat.range / f.long.label.pos)
long.line.strt <- max.lat
long.line.end <- long.lab.pos.1
} else if (pole == "S") {
if (!length(lat.ax.vals)) {
lat.ax.vals <- seq(max.lat - d.lat.ax.vals, min.lat, by = -d.lat.ax.vals)
}
outer.lat.ax.val <- max.lat
inner.lat.ax.val <- ifelse(min.lat == -90, NA, min.lat)
long.lab.pos.1 <- outer.lat.ax.val + (lat.range / f.long.label.ticks)
long.lab.pos.2 <- outer.lat.ax.val + (lat.range / f.long.label.pos)
long.line.strt <- long.lab.pos.1
long.line.end <- min.lat
}
lat.ax.vals <- lat.ax.vals[abs(lat.ax.vals) != 90]
lat.ax.labs <- paste0(ifelse(lat.ax.vals < 0, -lat.ax.vals, lat.ax.vals),
degree.sym, ifelse(lat.ax.vals < 0, " S", " N"))
# Define the x axes required
if (!length(long.ax.vals)) {
long.ax.vals <- seq(min.lon, max.lon, by = longitude.spacing)
}
if (!is.segment) {
long.ax.vals <- long.ax.vals[long.ax.vals != -180]
}
long.ax.labs <- paste0(abs(long.ax.vals), degree.sym,
ifelse(long.ax.vals <= 0, " W", " E"))
long.ax.labs[long.ax.vals == 0] <- paste0(0, degree.sym)
long.ax.labs[long.ax.vals == 180] <- paste0(180, degree.sym, " W")
lat.lines <- expand.grid(long = min.lon : max.lon, lat = lat.ax.vals)
# Define rotation angle for longitude labels
if (rotate.long.labels) {
if (pole == "N") {
long.ax.lab.rotation <- long.ax.vals - 180 - rotate.to
if (is.segment) long.ax.lab.rotation <- long.ax.lab.rotation + 180
} else {
long.ax.lab.rotation <- -long.ax.vals + rotate.to
}
} else {
long.ax.lab.rotation <- 0
}
# Get map outline and crop
if (is.segment | (pole == "N")) {
if (plot.political.boundaries) {
map.outline <- raster::crop(ne_land_50_political,
raster::extent(min.lon, max.lon,
min.lat, max.lat),
snap = "in")
} else {
map.outline <- raster::crop(ne_land_50,
raster::extent(min.lon, max.lon,
min.lat, max.lat),
snap = "in")
}
} else {
# Use different map source for south polar full longitude plot
# to circumvent buggy line at 180 deg W
map.outline <- ggplot2::map_data("world", "Antarctica")
i <- which(map.outline$lat >= min.lat & map.outline$lat <= max.lat)
map.outline <- map.outline[i, ]
}
if (!length(data.layer)) {
p <- ggplot2::ggplot()
} else {
p <- data.layer
}
p <- p +
# Plot map outline and project to polar coordinates
ggplot2::geom_polygon(data = map.outline,
ggplot2::aes(x = .data$long, y = .data$lat,
group = .data$group),
fill = land.fill.colour, size = size,
colour = land.outline.colour) +
ggplot2::coord_map("ortho",
orientation = c(ifelse(pole == "N", 90, -90),
rotate.to, 0),
xlim = c(min.lon, max.lon), clip = clip
) +
# Remove axes and labels
ggplot2::scale_x_continuous("", breaks = NULL) +
ggplot2::scale_y_continuous("", breaks = NULL) +
# Outer latitude axis
ggplot2::geom_line(
ggplot2::aes(y = outer.lat.ax.val, x = min.lon : max.lon),
size = size.outer, colour = "black")
# Inner latitude axis
if (!is.na(inner.lat.ax.val)) {
p <- p + ggplot2::geom_line(
ggplot2::aes(y = inner.lat.ax.val, x = min.lon : max.lon),
size = size.outer, colour = "black")
}
# Change theme to remove panel backgound
p <- p + ggplot2::theme(panel.background = ggplot2::element_blank())
# Add axes and labels
# Lat axis lines
if (plt.lat.axes) {
p <- p + ggplot2::geom_line(data = lat.lines,
ggplot2::aes(y = .data$lat, x = .data$long,
group = .data$lat),
size = size.axes, linetype = "dashed",
colour = "black")
}
# Lat axis labels
if (plt.lat.labels) {
if (!length(lat.ax.labs.pos)) {
lat.ax.labs.pos <- mean.lon
}
p <- p + ggplot2::geom_label(
ggplot2::aes(x = lat.ax.labs.pos, y = lat.ax.vals,
label = lat.ax.labs),
size = ax.labs.size,
alpha = 0.75, label.size = 0)
}
# Longitude axis lines
if (plt.lon.axes) {
p <- p + ggplot2::geom_segment(
ggplot2::aes(y = long.line.strt, yend = long.line.end,
x = long.ax.vals, xend = long.ax.vals),
linetype = "dashed", colour = "black", size = size.axes)
}
# Longitude axis labels
if (plt.lon.labels) {
p <- p + ggplot2::geom_text(
ggplot2::aes(x = long.ax.vals,
y = long.lab.pos.2,
label = long.ax.labs,
angle = long.ax.lab.rotation),
size = ax.labs.size)
}
# If segment add lines to edge
if (is.segment) {
p <- p + ggplot2::geom_segment(
ggplot2::aes(y = long.line.strt, yend = long.line.end,
x = c(min.lon, max.lon), xend = c(min.lon, max.lon)),
colour = "black", size = size.outer)
}
p
}
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Defines functions ggpolar
Documented in ggpolar
#' Nicely formatted polar ggplot
#'
#' Produce nicely formatted maps of the Arctic or Antarctic in polar
#' projection. Also works for longitudinal segments, e.g. just Greenland.
#'
#' @param pole character; which pole: north ("N") or south ("S")? Note that
#' full-longitude south polar plots only include the Antarctic main land,
#' irrespective of the latitude setting.
#' @param data.layer optional ggplot2 layer of data onto which the polar map
#' shall be plotted. Defaults to \code{NULL} which only plots the map.
#' @param max.lat maximum latitude in degree.
#' @param min.lat minimum latitude in degree.
#' @param max.lon maximum longitude in degree.
#' @param min.lon minimum longitude in degree.
#' @param longitude.spacing interval between longitude axis tick marks.
#' @param n.lat.labels approximate number of latitude tick marks.
#' @param plot.political.boundaries logical; should political (country)
#' boundaries be plotted? Defaults to FALSE.
#' @param land.fill.colour colour to shade the land (default "Grey").
#' @param land.outline.colour colour for the land surface outlines (default
#' "Black"); set to the same colour as \code{land.fill.colour} to hide
#' them. This parameter also controls the colours of the political boundaries,
#' if they are switched on.
#' @param rotate logical; if plotting a segment of < 360 degrees longitude,
#' rotate the plot so that north is up (or south is down) as seen from the
#' mean longitude of the segment.
#' @param nearest.x.degrees round latitude tickmarks to how many degrees?
#' @param lat.ax.vals manually set the latitude axis values where to plot
#' latitude labels and lines. This overrides the automatic setting by
#' \code{n.lat.labels} and \code{x.nearest.degress}, while the default
#' \code{NULL} means to use the automatic setting.
#' @param long.ax.vals manually set the longitude axis values where to plot
#' longitude labels and lines. This overrides the automatic setting by
#' \code{longitude.spacing}, while the default \code{NULL} means to use the
#' automatic setting.
#' @param plt.lat.axes logical; shall latitude axes be plotted?
#' @param plt.lat.labels logical; shall latitude labels be plotted? Per default
#' set to the value of \code{plt.lat.axes}.
#' @param plt.lon.axes logical; shall longitude axes be plotted?
#' @param plt.lon.labels logical; shall longitude labels be plotted? Per default
#' set to the value of \code{plt.lon.axes}.
#' @param f.long.label.ticks fraction of the plotted latitude axis range by
#' which the longitude ticksmarks extend behind the outer latitude axis,
#' i.e. the minimum (maximum) latitude for north (south) polar plots.
#' @param f.long.label.pos fraction of the plotted latitude axis range by
#' which the longitude labels are offset from the outer latitude axis.
#' @param rotate.long.labels logical; controls whether the longitude axis labels
#' are rotated according to their value and the setting of \code{rotate} (the
#' default) or not.
#' @param lat.ax.labs.pos longitudinal positions of the latitude axis
#' labels. Per default, the labels are placed at 0 E (180 W) for north (south)
#' polar plots or at the mean longitude of a segment; use this parameter to
#' override the default setting.
#' @param ax.labs.size size in mm of latitude and longitude axis labels.
#' @param size size in mm of the continental and land outlines.
#' @param size.axes size in mm of the latitude and longitude axes.
#' @param size.outer size in mm of the outer (and potential inner) longitude
#' circle and, if plotting a segment, of the outer latitude lines.
#' @param clip Should drawing be clipped to the extent of the plot panel? A
#' setting of \code{"on"} (the default) means yes, and a setting of
#' \code{"off"} means no. For details, please see
#' \code{\link[ggplot2]{coord_cartesian}}.
#' @importFrom rlang .data
#' @author Andrew Dolman <andrew.dolman@awi.de> with some modifications by
#' Thomas Münch.
#' @source Code adapted from Mikey Harper's plot; see
#' https://stackoverflow.com/a/49084793.
#'
#' Coastlines and political boundaries for complete north polar plots, and for
#' north and south polar segment plots, have been obtained from the
#' rnaturalearth package:
#' https://cran.r-project.org/web/packages/rnaturalearth/index.html
#'
#' Complete south polar plots use ggplot2 data.
#' @examples
#'
#' # full north polar plot
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4)
#'
#' # with political boundaries
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
#' plot.political.boundaries = TRUE)
#'
#' # hide land surface outlines
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55, n.lat.labels = 4,
#' land.outline.colour = "Grey")
#'
#' # full south polar plot
#' ggpolar(pole = "S", max.lat = -60, min.lat = -90)
#'
#' # north polar segment plot with adjusted longitude and latitude labelling
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55,
#' max.lon = 0, min.lon = -80,
#' longitude.spacing = 15, n.lat.labels = 5)
#'
#' # rotate the segment
#' ggpolar(pole = "N", max.lat = 90, min.lat = 55,
#' max.lon = 0, min.lon = -80,
#' longitude.spacing = 15, n.lat.labels = 5,
#' rotate = TRUE)
#'
#' # south polar segment plot
#' ggpolar(pole = "S", max.lat = -55, min.lat = -90,
#' max.lon = 80, min.lon = -20,
#' longitude.spacing = 30, rotate = TRUE)
#'
#' # it is also possible to plot a ring segment;
#' # additionally, there are various options to cuzstomize position and look of
#' # axis labels etc., with a few examples shown here
#' ggpolar(pole = "N", max.lat = 85, min.lat = 57.5,
#' max.lon = -10, min.lon = -75, rotate = TRUE,
#' lat.ax.vals = c(60, 70, 80), # explicitly specify latitude labels
#' long.ax.vals = -c(20, 40, 60), # explicitly specify longitude labels
#' f.long.label.ticks = Inf, # don't draw longitude lines beyond segment
#' f.long.label.pos = 15, # adjust label position from segment outline
#' rotate.long.labels = FALSE, # don't rotate longitude labels
#' lat.ax.labs.pos = -75 - c(3.5, 5, 10), # move latitude labels to left side
#' ax.labs.size = 4.75) # larger labels
#'
#' # ---------------------------------------------------------------------------
#'
#' # if you want to add points or a spatial field of data to a ggpolar plot, it
#' # can be convenient to create that plot separately and then provide it as an
#' # argument to ggpolar, so that it can be added to the polar plot internally:
#'
#' library(ggplot2)
#'
#' # create some dummy data
#' nx <- 360 / 5
#' ny <- 30 / 5
#'
#' lon <- seq(0, 355, length.out = nx)
#' lat <- seq(-65, -90, length.out = ny)
#'
#' df <- data.frame(lon = rep(lon, times = ny), lat = rep(lat, each = nx),
#' dat = runif(n = nx * ny, min = -1, max = 1))
#'
#' # Colorbrewer2 colour scales for plotting the "correlation" data can be
#' # obtained directly with the respective grfxtools function
#' colour.scale <- ColorPal("RdBu", rev = TRUE)
#'
#' # create ggplot for data
#' p <- ggplot() +
#' geom_tile(aes(x = lon, y = lat, fill = dat),
#' data = df, colour = "transparent") +
#' scale_fill_gradientn(colours = colour.scale,
#' limits = c(-1, 1),
#' name = "Correlation") +
#' theme(legend.key.height = unit(0.75, units = "inches"),
#' legend.text = element_text(size = 18),
#' legend.title = element_text(size = 18),
#' text = element_text(size = 18))
#'
#' # plot data projected on south polar map
#' ggpolar(pole = "S", data.layer = p,
#' max.lat = -60, min.lat = -90, n.lat.labels = 3,
#' longitude.spacing = 45,
#' land.fill.colour = "transparent")
#'
#' # ---------------------------------------------------------------------------
#'
#' \dontrun{
#' ggpolar(pole = "W", max.lat = -55, min.lat = -90)
#' ggpolar(pole = "S", max.lat = 90, min.lat = 55)
#' ggpolar(pole = "S", max.lat = -90, min.lat = -55)
#' }
#' @export
ggpolar <- function(pole = c("N", "S"), data.layer = NULL, max.lat, min.lat,
max.lon = 180, min.lon = -180, longitude.spacing = 60,
n.lat.labels = 4, plot.political.boundaries = FALSE,
land.fill.colour = "Grey", land.outline.colour = "Black",
rotate = FALSE, nearest.x.degrees = 5,
lat.ax.vals = NULL, long.ax.vals = NULL,
plt.lat.axes = TRUE, plt.lat.labels = plt.lat.axes,
plt.lon.axes = TRUE, plt.lon.labels = plt.lon.axes,
f.long.label.ticks = 20, f.long.label.pos = 7,
rotate.long.labels = TRUE, lat.ax.labs.pos = NULL,
ax.labs.size = 4, size = 0.5, size.axes = 0.25,
size.outer = 1, clip = "on") {
pole <- match.arg(pole, choices = c("N", "S"))
if (pole == "N" & max.lat < 0) stop("If pole == N, max.lat should be positive")
if (pole == "S" & min.lat > 0) stop("If pole == S, min.lat should be negative")
# degree symbol
degree.sym <- "\u00b0"
stopifnot(max.lat > min.lat)
stopifnot(max.lon <= 180 & min.lon >= -180 & max.lat <= 90 & min.lat >= -90)
is.segment <- (min.lon == -180 & max.lon == 180) == FALSE
mean.lon <- mean(c(min.lon, max.lon))
# if not a segment
if (!is.segment) {
mean.lon <- ifelse(pole == "N", 0, 180)
}
rotate.to <- 0
if (rotate & is.segment) {rotate.to <- mean.lon}
lat.range <- abs(max.lat - min.lat)
d.lat.ax.vals <- nearest.x.degrees *
round((max.lat - min.lat)/n.lat.labels/nearest.x.degrees)
# Hemisphere specific values
if (pole == "N") {
if (!length(lat.ax.vals)) {
lat.ax.vals <- seq(min.lat + d.lat.ax.vals, max.lat, by = d.lat.ax.vals)
}
outer.lat.ax.val <- min.lat
inner.lat.ax.val <- ifelse(max.lat == 90, NA, max.lat)
long.lab.pos.1 <- outer.lat.ax.val - (lat.range / f.long.label.ticks)
long.lab.pos.2 <- outer.lat.ax.val - (lat.range / f.long.label.pos)
long.line.strt <- max.lat
long.line.end <- long.lab.pos.1
} else if (pole == "S") {
if (!length(lat.ax.vals)) {
lat.ax.vals <- seq(max.lat - d.lat.ax.vals, min.lat, by = -d.lat.ax.vals)
}
outer.lat.ax.val <- max.lat
inner.lat.ax.val <- ifelse(min.lat == -90, NA, min.lat)
long.lab.pos.1 <- outer.lat.ax.val + (lat.range / f.long.label.ticks)
long.lab.pos.2 <- outer.lat.ax.val + (lat.range / f.long.label.pos)
long.line.strt <- long.lab.pos.1
long.line.end <- min.lat
}
lat.ax.vals <- lat.ax.vals[abs(lat.ax.vals) != 90]
lat.ax.labs <- paste0(ifelse(lat.ax.vals < 0, -lat.ax.vals, lat.ax.vals),
degree.sym, ifelse(lat.ax.vals < 0, " S", " N"))
# Define the x axes required
if (!length(long.ax.vals)) {
long.ax.vals <- seq(min.lon, max.lon, by = longitude.spacing)
}
if (!is.segment) {
long.ax.vals <- long.ax.vals[long.ax.vals != -180]
}
long.ax.labs <- paste0(abs(long.ax.vals), degree.sym,
ifelse(long.ax.vals <= 0, " W", " E"))
long.ax.labs[long.ax.vals == 0] <- paste0(0, degree.sym)
long.ax.labs[long.ax.vals == 180] <- paste0(180, degree.sym, " W")
lat.lines <- expand.grid(long = min.lon : max.lon, lat = lat.ax.vals)
# Define rotation angle for longitude labels
if (rotate.long.labels) {
if (pole == "N") {
long.ax.lab.rotation <- long.ax.vals - 180 - rotate.to
if (is.segment) long.ax.lab.rotation <- long.ax.lab.rotation + 180
} else {
long.ax.lab.rotation <- -long.ax.vals + rotate.to
}
} else {
long.ax.lab.rotation <- 0
}
# Get map outline and crop
if (is.segment | (pole == "N")) {
if (plot.political.boundaries) {
map.outline <- raster::crop(ne_land_50_political,
raster::extent(min.lon, max.lon,
min.lat, max.lat),
snap = "in")
} else {
map.outline <- raster::crop(ne_land_50,
raster::extent(min.lon, max.lon,
min.lat, max.lat),
snap = "in")
}
} else {
# Use different map source for south polar full longitude plot
# to circumvent buggy line at 180 deg W
map.outline <- ggplot2::map_data("world", "Antarctica")
i <- which(map.outline$lat >= min.lat & map.outline$lat <= max.lat)
map.outline <- map.outline[i, ]
}
if (!length(data.layer)) {
p <- ggplot2::ggplot()
} else {
p <- data.layer
}
p <- p +
# Plot map outline and project to polar coordinates
ggplot2::geom_polygon(data = map.outline,
ggplot2::aes(x = .data$long, y = .data$lat,
group = .data$group),
fill = land.fill.colour, size = size,
colour = land.outline.colour) +
ggplot2::coord_map("ortho",
orientation = c(ifelse(pole == "N", 90, -90),
rotate.to, 0),
xlim = c(min.lon, max.lon), clip = clip
) +
# Remove axes and labels
ggplot2::scale_x_continuous("", breaks = NULL) +
ggplot2::scale_y_continuous("", breaks = NULL) +
# Outer latitude axis
ggplot2::geom_line(
ggplot2::aes(y = outer.lat.ax.val, x = min.lon : max.lon),
size = size.outer, colour = "black")
# Inner latitude axis
if (!is.na(inner.lat.ax.val)) {
p <- p + ggplot2::geom_line(
ggplot2::aes(y = inner.lat.ax.val, x = min.lon : max.lon),
size = size.outer, colour = "black")
}
# Change theme to remove panel backgound
p <- p + ggplot2::theme(panel.background = ggplot2::element_blank())
# Add axes and labels
# Lat axis lines
if (plt.lat.axes) {
p <- p + ggplot2::geom_line(data = lat.lines,
ggplot2::aes(y = .data$lat, x = .data$long,
group = .data$lat),
size = size.axes, linetype = "dashed",
colour = "black")
}
# Lat axis labels
if (plt.lat.labels) {
if (!length(lat.ax.labs.pos)) {
lat.ax.labs.pos <- mean.lon
}
p <- p + ggplot2::geom_label(
ggplot2::aes(x = lat.ax.labs.pos, y = lat.ax.vals,
label = lat.ax.labs),
size = ax.labs.size,
alpha = 0.75, label.size = 0)
}
# Longitude axis lines
if (plt.lon.axes) {
p <- p + ggplot2::geom_segment(
ggplot2::aes(y = long.line.strt, yend = long.line.end,
x = long.ax.vals, xend = long.ax.vals),
linetype = "dashed", colour = "black", size = size.axes)
}
# Longitude axis labels
if (plt.lon.labels) {
p <- p + ggplot2::geom_text(
ggplot2::aes(x = long.ax.vals,
y = long.lab.pos.2,
label = long.ax.labs,
angle = long.ax.lab.rotation),
size = ax.labs.size)
}
# If segment add lines to edge
if (is.segment) {
p <- p + ggplot2::geom_segment(
ggplot2::aes(y = long.line.strt, yend = long.line.end,
x = c(min.lon, max.lon), xend = c(min.lon, max.lon)),
colour = "black", size = size.outer)
}
p
}
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