settled-reach/tooling/planet-gen/sol_data/ice_moons.py

"""
Ice moon terrain builder — Europa, Ganymede, Callisto, Enceladus.

These bodies lack high-quality global DEMs. We use available mosaics
(albedo/reflectance) to derive synthetic elevation:
  - Bright = ice ridges/highlands (high)
  - Dark = mare/chaos terrain/craters (low)

Each moon gets specific temperature and appearance tuning.
"""

import numpy as np
from pathlib import Path
from scipy.ndimage import gaussian_filter

from sol_data.download import ensure_cached
from sol_data.shared import (
    GRID_W, GRID_H,
    load_image_as_elevation, resample_to_grid, normalize_01,
    compute_hillshade, assemble_terrain,
    temperature_grid_analytical,
)

# ─── Per-moon configuration ─────────────────────────────────────────────────

MOON_CONFIG = {
    "GJ0f-2": {  # Europa
        "name": "Europa",
        "mosaic_url": "https://astrogeology.usgs.gov/cache/images/3c79b3867c0dc5ec2ea33e485a079e58_europa_voyager_galileo_ssi_global_mosaic_500m.jpg",
        "mosaic_file": "europa_galileo_mosaic.jpg",
        "base_temp_K": 102.0,
        "lat_gradient_K": 10.0,
        "sigma": 2.0,         # smooth albedo → elevation
        "invert_albedo": False,  # bright = ridges (high)
    },
    "GJ0f-3": {  # Ganymede
        "name": "Ganymede",
        "mosaic_url": "https://astrogeology.usgs.gov/cache/images/f60b3c06c92f59834f2d4cf9b46cb8f7_ganymede_voyager_galileo_global_mosaic_1km.jpg",
        "mosaic_file": "ganymede_galileo_mosaic.jpg",
        "base_temp_K": 110.0,
        "lat_gradient_K": 15.0,
        "sigma": 3.0,
        "invert_albedo": False,
    },
    "GJ0f-4": {  # Callisto
        "name": "Callisto",
        "mosaic_url": "https://astrogeology.usgs.gov/cache/images/26b4e80eeb35d46c53d56cded56deeef_callisto_voyager_galileo_global_mosaic_1km.jpg",
        "mosaic_file": "callisto_galileo_mosaic.jpg",
        "base_temp_K": 115.0,
        "lat_gradient_K": 12.0,
        "sigma": 4.0,
        "invert_albedo": False,
    },
    "GJ0g-2": {  # Enceladus
        "name": "Enceladus",
        "mosaic_url": "https://astrogeology.usgs.gov/cache/images/1e9fede316c8c47fdc0b96f4c09e4915_enceladus_cassini_iss_global_mosaic_100m.jpg",
        "mosaic_file": "enceladus_cassini_mosaic.jpg",
        "base_temp_K": 75.0,
        "lat_gradient_K": 8.0,
        "sigma": 2.0,
        "invert_albedo": False,
    },
}


def _load_mosaic_as_elevation(config: dict) -> np.ndarray:
    """Load a global mosaic and convert to synthetic elevation."""
    try:
        path = ensure_cached(config["mosaic_url"], config["mosaic_file"])
        print(f"    loading {config['name']} mosaic: {path}")
        albedo = load_image_as_elevation(str(path),
                                          invert=config.get("invert_albedo", False))
        albedo = resample_to_grid(albedo, GRID_H, GRID_W, order=1)
    except Exception as e:
        print(f"    WARNING: {config['name']} mosaic unavailable ({e}), synthetic")
        albedo = _synthetic_ice_terrain(config["name"])

    # Smooth albedo to create plausible topography
    sigma = config.get("sigma", 3.0)
    elevation = gaussian_filter(albedo, sigma=sigma)
    return normalize_01(elevation)


def _synthetic_ice_terrain(name: str) -> np.ndarray:
    """Generate synthetic ice moon terrain if mosaic unavailable."""
    seed = hash(name) & 0xFFFFFFFF
    rng = np.random.default_rng(seed)
    base = rng.random((GRID_H, GRID_W)).astype(np.float32)
    base = gaussian_filter(base, sigma=6.0)
    # Add craters
    for _ in range(20):
        cy, cx = rng.integers(0, GRID_H), rng.integers(0, GRID_W)
        r = rng.integers(5, 20)
        y, x = np.ogrid[-cy:GRID_H-cy, -cx:GRID_W-cx]
        mask = x*x + y*y <= r*r
        base[mask] *= 0.5
    return normalize_01(base)


def build_terrain(body_def: dict) -> dict:
    """Build ice moon terrain dict from mosaic data."""
    import sys
    sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
    from planet_simulation import compute_biome

    body_id = body_def["id"]
    config = MOON_CONFIG.get(body_id)

    if config is None:
        raise ValueError(f"No ice moon config for {body_id}")

    print(f"  {config['name']}: loading data...")

    # ── 1. Elevation ────────────────────────────────────────────────────
    elevation = _load_mosaic_as_elevation(config)
    sea_level = 0.0
    surface_water = np.zeros((GRID_H, GRID_W), dtype=bool)

    # ── 2. Temperature ──────────────────────────────────────────────────
    temperature_K = temperature_grid_analytical(
        base_T_K=config["base_temp_K"],
        elevation=elevation,
        lapse_rate_K_per_unit=5.0,
        lat_gradient_K=config["lat_gradient_K"],
    )
    temperature_K = np.maximum(temperature_K, 40.0)

    # ── 3. Moisture ─────────────────────────────────────────────────────
    moisture = np.zeros((GRID_H, GRID_W), dtype=np.float32)

    # ── 4. Biome ────────────────────────────────────────────────────────
    biome = compute_biome(body_def, elevation, sea_level, surface_water,
                          temperature_K, moisture)

    # ── 5. Hillshade ────────────────────────────────────────────────────
    hillshade = compute_hillshade(elevation)

    return assemble_terrain(
        elevation=elevation, temperature_K=temperature_K,
        moisture=moisture, biome=biome,
        surface_water=surface_water, hillshade=hillshade,
        rivers=[], sea_level=sea_level,
    )