Flat projection of 60 degrees south with initial claimants

south_pole_60S.py

# %%
"""
Antarctic Territorial Claims — Flat Polar View

Top-down South Polar Stereographic map showing the seven national
territorial claims on Antarctica, with flags and color-coded labels
arranged around the 60°S circle.

Background imagery: Natural Earth shaded relief (stock_img).
"""

import cartopy.crs as ccrs
import matplotlib.path as mpath
import matplotlib.pyplot as plt
import numpy as np
from matplotlib.offsetbox import AnnotationBbox, OffsetImage
from PIL import Image, ImageOps

# ── Configuration ─────────────────────────────────────────────────────

FLAG_DIR = "/tmp/flags"
OUTPUT = "south_pole_60S.png"

# Antarctic territorial claims: (lon_start, lon_end, color, country_code, label)
# Use None for label when a country has a split territory (e.g. Australia)
TERRITORIES = [
    (-74, -25, "#4e79a7", "ar", "Argentina"),
    (45, 136, "#f28e2b", "au", "Australia"),
    (142, 160, "#f28e2b", "au", None),  # Australia's eastern sector
    (-90, -53, "#e15759", "cl", "Chile"),
    (136, 142, "#b07aa1", "fr", "France"),
    (160, 210, "#59a14f", "nz", "New Zealand"),
    (-20, 45, "#76b7b2", "no", "Norway"),
    (-80, -20, "#ff9da7", "gb", "United Kingdom"),
]

# Override the default midpoint angle for overlapping claims
# (Argentina and UK share nearly the same midpoint longitude)
ANGLE_OVERRIDES = {"ar": -40, "gb": -60}

PLATE_CARREE = ccrs.PlateCarree()
PROJ = ccrs.SouthPolarStereo()


# ── Helpers ───────────────────────────────────────────────────────────


def make_circular_boundary() -> mpath.Path:
    """Create a circular clipping path for the polar axes."""
    theta = np.linspace(0, 2 * np.pi, 100)
    verts = np.vstack([np.sin(theta), np.cos(theta)]).T
    return mpath.Path(verts * 0.5 + 0.5)


def draw_territory_wedge(
    ax, lon_start: float, lon_end: float, color: str,
    lat_inner: float = -90, lat_outer: float = -60, alpha: float = 0.20,
):
    """Draw a filled wedge from the pole to 60°S between two longitudes,
    with a dashed outline."""
    n_points = max(int(abs(lon_end - lon_start)) * 2, 10)
    lons_arc = np.linspace(lon_start, lon_end, n_points)
    lons = np.concatenate([lons_arc, lons_arc[::-1], [lons_arc[0]]])
    lats = np.concatenate([
        np.full_like(lons_arc, lat_outer),
        np.full_like(lons_arc, lat_inner),
        [lat_outer],
    ])
    ax.fill(lons, lats, transform=PLATE_CARREE, color=color, alpha=alpha)
    ax.plot(lons, lats, transform=PLATE_CARREE, color=color, lw=0.8, ls="--", alpha=0.6)


def compute_axes_geometry(fig, ax):
    """Compute the axes center and radius in figure-fraction coordinates."""
    fig.canvas.draw()
    renderer = fig.canvas.get_renderer()
    ax_box = ax.get_window_extent(renderer)
    fig_box = fig.bbox
    cx = (ax_box.x0 + ax_box.x1) / 2 / fig_box.width
    cy = (ax_box.y0 + ax_box.y1) / 2 / fig_box.height
    r = min(ax_box.width, ax_box.height) / 2 / fig_box.width
    return cx, cy, r


def compute_60s_radius(fig, ax) -> float:
    """Find the radius of the 60°S circle in figure-fraction units."""
    r60_proj = abs(PROJ.transform_point(0, -60, PLATE_CARREE)[1])
    pt_center = ax.transData.transform((0, 0))
    pt_60 = ax.transData.transform((0, r60_proj))
    return abs(pt_60[1] - pt_center[1]) / fig.bbox.height


def add_flag_with_shadow(fig, flag_code: str, x: float, y: float, zoom: float = 0.75):
    """Place a flag image at (x, y) in figure-fraction coordinates,
    with a white border and subtle drop shadow."""
    flag = Image.open(f"{FLAG_DIR}/{flag_code}.png").convert("RGBA")
    flag = ImageOps.expand(flag, border=3, fill="white")

    shadow_px = 2
    w, h = flag.size
    canvas = Image.new("RGBA", (w + shadow_px * 2, h + shadow_px * 2), (0, 0, 0, 0))
    shadow = Image.new("RGBA", flag.size, (0, 0, 0, 40))
    canvas.paste(shadow, (shadow_px * 2, shadow_px * 2))
    canvas.paste(flag, (0, 0), flag)

    ab = AnnotationBbox(
        OffsetImage(np.array(canvas), zoom=zoom),
        (x, y), xycoords="figure fraction", frameon=False,
    )
    fig.add_artist(ab)


def label_alignment(angle_deg: float, fx: float, fy: float):
    """Determine text position and alignment based on which side of
    the circle the flag sits on."""
    angle_deg = angle_deg % 360
    if 45 < angle_deg < 135:  # right side
        return fx + 0.055, fy, "left", "center"
    elif 225 < angle_deg < 315:  # left side
        return fx - 0.055, fy, "right", "center"
    elif angle_deg <= 45 or angle_deg >= 315:  # top
        return fx, fy + 0.045, "center", "bottom"
    else:  # bottom
        return fx, fy - 0.045, "center", "top"


# ── Build the map ─────────────────────────────────────────────────────

fig = plt.figure(figsize=(11, 11), facecolor="white")
ax = fig.add_axes([0.08, 0.08, 0.84, 0.84], projection=PROJ)
ax.set_extent([-180, 180, -90, -50], PLATE_CARREE)
ax.set_boundary(make_circular_boundary(), transform=ax.transAxes)

# Background imagery
ax.stock_img()
ax.coastlines(lw=0.6, color="#4a4a4a", zorder=2)
ax.gridlines(draw_labels=False, color="white", alpha=0.15, lw=0.5)
ax.patch.set_visible(False)

# Territory wedges
for lon0, lon1, color, _, _ in TERRITORIES:
    draw_territory_wedge(ax, lon0, lon1, color)

# 60°S circle
circle_lons = np.linspace(0, 360, 361)
ax.plot(
    circle_lons, np.full_like(circle_lons, -60),
    color="#d63031", lw=2, transform=PLATE_CARREE,
    ls=(0, (8, 4)), zorder=5,
)

# ── Place flags and labels ────────────────────────────────────────────

ax_cx, ax_cy, _ = compute_axes_geometry(fig, ax)
r60 = compute_60s_radius(fig, ax)
flag_r = r60 * 1.05   # flags sit just outside the 60°S circle
edge_r = r60           # connectors start at the circle

placed = set()
for lon0, lon1, color, code, label in TERRITORIES:
    if label is None or code in placed:
        continue
    placed.add(code)

    # Determine the angular position for this flag
    mid_lon = ANGLE_OVERRIDES.get(code, (lon0 + lon1) / 2)
    angle = np.deg2rad(mid_lon)
    sin_a, cos_a = np.sin(angle), np.cos(angle)

    # Flag and connector positions in figure-fraction coordinates
    # (SouthPolarStereo: 0° longitude at top, longitude increases clockwise)
    fx = ax_cx + flag_r * sin_a
    fy = ax_cy + flag_r * cos_a
    ex = ax_cx + edge_r * sin_a
    ey = ax_cy + edge_r * cos_a

    add_flag_with_shadow(fig, code, fx, fy)

    # Connector line from 60°S circle to flag
    fig.add_artist(plt.Line2D(
        [ex, fx], [ey, fy],
        transform=fig.transFigure,
        color=color, lw=1.5, alpha=0.8,
        solid_capstyle="round", clip_on=False,
    ))

    # Anchor dot at the circle edge
    fig.add_artist(plt.Line2D(
        [ex], [ey],
        transform=fig.transFigure,
        marker="o", markersize=4, color=color,
        lw=0, clip_on=False,
    ))

    # Color-coded label
    tx, ty, ha, va = label_alignment(np.rad2deg(angle), fx, fy)
    fig.text(
        tx, ty, label,
        ha=ha, va=va,
        fontsize=11, fontweight="bold", fontstyle="italic",
        color=color,
        bbox=dict(boxstyle="round,pad=0.15", fc="white", ec="none", alpha=1.0),
    )

# ── 60°S annotation ──────────────────────────────────────────────────
# Place "60°S" inline at the top of the red dashed circle.
# In projected coordinates, the topmost point is at (0, +r60).
r60_proj_y = abs(PROJ.transform_point(0, -60, PLATE_CARREE)[1])
top_disp = ax.transData.transform((0, r60_proj_y))
top_fig = fig.transFigure.inverted().transform(top_disp)
fig.text(
    top_fig[0], top_fig[1], " 60°S ",
    ha="center", va="center",
    fontsize=8.5, color="#d63031", fontweight="bold", fontstyle="italic",
    bbox=dict(boxstyle="round,pad=0.15", fc="white", ec="none", alpha=0.9),
    transform=fig.transFigure,
)

fig.savefig(OUTPUT, dpi=200, transparent=True)
print(f"Saved {OUTPUT}")