feat(pygal): implement area-elevation-profile (#4888)

## Implementation: `area-elevation-profile` - pygal

Implements the **pygal** version of `area-elevation-profile`.

**File:** `plots/area-elevation-profile/implementations/pygal.py`

**Parent Issue:** #4578

---
:robot: *[impl-generate
workflow](https://github.com/MarkusNeusinger/pyplots/actions/runs/23120069560)*

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: github-actions[bot]

plots/area-elevation-profile/implementations/pygal.py

@@ -0,0 +1,244 @@
+""" pyplots.ai
+area-elevation-profile: Terrain Elevation Profile Along Transect
+Library: pygal 3.1.0 | Python 3.14.3
+Quality: 86/100 | Created: 2026-03-15
+"""
+
+import re
+import xml.etree.ElementTree as ET
+
+import cairosvg
+import numpy as np
+import pygal
+from pygal.style import Style
+
+
+# Data - Alpine hiking trail elevation profile (120 km transect, sampled every ~1 km)
+np.random.seed(42)
+
+distances_km = np.linspace(0, 120, 200)
+
+# Build realistic terrain with multiple peaks and valleys
+base_terrain = (
+    800
+    + 600 * np.sin(distances_km * np.pi / 40) ** 2
+    + 400 * np.sin(distances_km * np.pi / 25 + 1.2) ** 2
+    + 300 * np.exp(-((distances_km - 55) ** 2) / 80)
+    + 500 * np.exp(-((distances_km - 85) ** 2) / 120)
+    - 200 * np.exp(-((distances_km - 30) ** 2) / 50)
+)
+noise = np.random.normal(0, 25, len(distances_km))
+elevation_m = base_terrain + noise
+elevation_m = np.maximum(elevation_m, 650)
+
+# Landmarks along the trail with types for visual differentiation
+landmarks = [
+    {"name": "Grindelwald", "km": 0, "type": "town"},
+    {"name": "Kleine Scheidegg", "km": 22, "type": "pass"},
+    {"name": "Lauterbrunnen", "km": 38, "type": "valley"},
+    {"name": "Mürren", "km": 55, "type": "summit"},
+    {"name": "Blüemlisalp Hut", "km": 72, "type": "hut"},
+    {"name": "Hohtürli Pass", "km": 85, "type": "pass"},
+    {"name": "Kandersteg", "km": 120, "type": "town"},
+]
+
+# Get elevation at landmark positions
+for lm in landmarks:
+    idx = np.argmin(np.abs(distances_km - lm["km"]))
+    lm["elev"] = float(elevation_m[idx])
+
+# Visual styling per landmark type
+TYPE_COLORS = {
+    "summit": "#b5342b",  # deep red for highest point
+    "pass": "#c45a00",  # orange for mountain passes
+    "hut": "#7b4ea0",  # purple for alpine huts (distinct from orange)
+    "valley": "#2a7f3f",  # green for valley floors
+    "town": "#306998",  # blue for towns/settlements
+}
+
+# Custom style with refined palette
+custom_style = Style(
+    background="white",
+    plot_background="white",
+    foreground="#2d2d2d",
+    foreground_strong="#2d2d2d",
+    foreground_subtle="#e8e8e8",
+    colors=("#4a7fb5", "#d4690e"),
+    font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    title_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    title_font_size=48,
+    label_font_size=36,
+    major_label_font_size=34,
+    value_font_size=28,
+    legend_font_size=30,
+    legend_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    label_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    major_label_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    value_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    opacity=0.65,
+    opacity_hover=0.75,
+    guide_stroke_color="#e8e8e8",
+    guide_stroke_dasharray="4,4",
+    major_guide_stroke_color="#d0d0d0",
+    major_guide_stroke_dasharray="6,4",
+    stroke_opacity=1.0,
+    stroke_opacity_hover=1.0,
+    tooltip_font_size=26,
+    tooltip_font_family="DejaVu Sans, Helvetica, Arial, sans-serif",
+    tooltip_border_radius=8,
+)
+
+# Chart - tightened y-range to frame data better (peak ~2009m)
+chart = pygal.XY(
+    width=4800,
+    height=2700,
+    title="Bernese Oberland Traverse · area-elevation-profile · pygal · pyplots.ai",
+    x_title="Distance (km)",
+    y_title="Elevation (m)",
+    style=custom_style,
+    fill=True,
+    show_dots=False,
+    stroke_style={"width": 4},
+    show_y_guides=True,
+    show_x_guides=False,
+    show_legend=True,
+    legend_at_bottom=True,
+    legend_box_size=24,
+    value_formatter=lambda x: f"{x:,.0f} m",
+    x_value_formatter=lambda x: f"{x:.0f} km",
+    interpolate="cubic",
+    interpolation_precision=300,
+    min_scale=5,
+    max_scale=10,
+    margin_bottom=80,
+    margin_left=100,
+    margin_right=140,
+    margin_top=60,
+    spacing=12,
+    tooltip_fancy_mode=True,
+    range=(500, 2200),
+    xrange=(0, 128),
+    show_minor_x_labels=False,
+    show_minor_y_labels=False,
+    truncate_legend=-1,
+    dynamic_print_values=True,
+    print_values=False,
+    show_x_labels=True,
+    show_y_labels=True,
+    x_labels_major_count=7,
+    y_labels_major_count=6,
+)
+
+# Elevation profile as filled XY series
+profile_data = [
+    {"value": (float(d), float(e)), "label": f"{d:.1f} km — {e:.0f} m"}
+    for d, e in zip(distances_km, elevation_m, strict=True)
+]
+chart.add("Elevation Profile", profile_data)
+
+# Landmark markers as separate series with visible dots
+landmark_data = [
+    {"value": (float(lm["km"]), lm["elev"]), "label": f"{lm['name']} — {lm['elev']:.0f} m"} for lm in landmarks
+]
+chart.add("Landmarks", landmark_data, fill=False, show_dots=True, dots_size=16, stroke=False)
+
+# Save interactive HTML version with pygal's native tooltip support
+chart.render_to_file("plot.html")
+
+# Render SVG for annotation post-processing
+svg_bytes = chart.render()
+SVG_NS = "http://www.w3.org/2000/svg"
+ET.register_namespace("", SVG_NS)
+ET.register_namespace("xlink", "http://www.w3.org/1999/xlink")
+root = ET.fromstring(svg_bytes)
+
+# Build parent map and find landmark circles (only dots from the Landmarks series)
+parent_map = {child: parent for parent in root.iter() for child in parent}
+circles = sorted(
+    [c for c in root.iter(f"{{{SVG_NS}}}circle") if float(c.get("r", "0")) > 3], key=lambda c: float(c.get("cx", "0"))
+)
+
+# Find plot bottom from horizontal guide paths (format: "M0.0 Y h...")
+
+plot_bottom_y = 0
+for path in root.iter(f"{{{SVG_NS}}}path"):
+    cls = path.get("class", "")
+    d = path.get("d", "")
+    if "guide" in cls and " h" in d:
+        m = re.match(r"M[\d.]+ ([\d.]+) h", d)
+        if m:
+            plot_bottom_y = max(plot_bottom_y, float(m.group(1)))
+
+# Label positioning: stagger closely-spaced labels to avoid overlap
+label_offsets = {
+    "Grindelwald": -42,
+    "Kleine Scheidegg": -42,
+    "Lauterbrunnen": -42,
+    "Mürren": -52,
+    "Blüemlisalp Hut": -70,
+    "Hohtürli Pass": -42,
+    "Kandersteg": -42,
+}
+
+ns = f"{{{SVG_NS}}}"
+for i, circle in enumerate(circles[: len(landmarks)]):
+    parent_elem = parent_map.get(circle)
+    if parent_elem is None:
+        continue
+
+    cx, cy = float(circle.get("cx", "0")), float(circle.get("cy", "0"))
+    lm = landmarks[i]
+    lm_color = TYPE_COLORS.get(lm["type"], "#c45a00")
+    y_off = label_offsets.get(lm["name"], -42)
+
+    # Text anchor based on position
+    if i == 0:
+        anchor, dx = "start", 10
+    elif i == len(landmarks) - 1:
+        anchor, dx = "end", -10
+    else:
+        anchor, dx = "middle", 0
+
+    # Vertical dashed marker line
+    vline = ET.SubElement(parent_elem, f"{ns}line")
+    for attr, val in [("x1", cx), ("y1", cy), ("x2", cx), ("y2", plot_bottom_y)]:
+        vline.set(attr, f"{val:.1f}")
+    vline.set("stroke", lm_color)
+    vline.set("stroke-width", "2")
+    vline.set("stroke-dasharray", "8,5")
+    vline.set("opacity", "0.55")
+
+    # Landmark name (bold, colored by type)
+    name_el = ET.SubElement(parent_elem, f"{ns}text")
+    name_el.set("x", f"{cx + dx:.1f}")
+    name_el.set("y", f"{cy + y_off:.1f}")
+    name_el.set("text-anchor", anchor)
+    name_el.set("font-size", "32")
+    name_el.set("font-family", "DejaVu Sans, Helvetica, Arial, sans-serif")
+    name_el.set("fill", lm_color)
+    name_el.set("font-weight", "bold")
+    name_el.text = lm["name"]
+
+    # Elevation label (gray, below name)
+    elev_el = ET.SubElement(parent_elem, f"{ns}text")
+    elev_el.set("x", f"{cx + dx:.1f}")
+    elev_el.set("y", f"{cy + y_off + 24:.1f}")
+    elev_el.set("text-anchor", anchor)
+    elev_el.set("font-size", "26")
+    elev_el.set("font-family", "DejaVu Sans, Helvetica, Arial, sans-serif")
+    elev_el.set("fill", "#555555")
+    elev_el.text = f"{lm['elev']:.0f} m"
+
+# Add vertical exaggeration note (spec requirement) - positioned bottom-right
+note_el = ET.SubElement(root, f"{ns}text")
+note_el.set("x", "4650")
+note_el.set("y", f"{plot_bottom_y + 48:.0f}")
+note_el.set("text-anchor", "end")
+note_el.set("font-size", "28")
+note_el.set("font-family", "DejaVu Sans, Helvetica, Arial, sans-serif")
+note_el.set("fill", "#555555")
+note_el.set("font-style", "italic")
+note_el.text = "Vertical exaggeration ~10\u00d7 for terrain visibility"
+
+# Convert to PNG
+cairosvg.svg2png(bytestring=ET.tostring(root, encoding="unicode").encode("utf-8"), write_to="plot.png")