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scripts/download_srtm.py

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+#!/usr/bin/env python3
+"""Download SRTM GL1 GeoTIFF tiles for a bounding box via OpenTopography."""
+
+from __future__ import annotations
+
+import argparse
+import math
+import sys
+from pathlib import Path
+
+import httpx
+
+OPENTOPOGRAPHY_URL = "https://portal.opentopography.org/API/globaldem"
+
+
+def tile_names_for_bbox(min_lat: float, min_lng: float, max_lat: float, max_lng: float) -> list[str]:
+  tiles: list[str] = []
+  for lat in range(math.floor(min_lat), math.ceil(max_lat)):
+    ns = "N" if lat >= 0 else "S"
+    for lng in range(math.floor(min_lng), math.ceil(max_lng)):
+      ew = "E" if lng >= 0 else "W"
+      tiles.append(f"{ns}{abs(lat):02d}{ew}{abs(lng):03d}")
+  return tiles
+
+
+def download_tile(tile: str, output_dir: Path, api_key: str | None) -> None:
+  params = {
+    "demtype": "SRTMGL1",
+    "south": int(tile[1:3]) * (1 if tile[0] == "N" else -1),
+    "north": int(tile[1:3]) * (1 if tile[0] == "N" else -1) + 1,
+    "west": int(tile[4:7]) * (1 if tile[3] == "E" else -1),
+    "east": int(tile[4:7]) * (1 if tile[3] == "E" else -1) + 1,
+    "outputFormat": "GTiff",
+  }
+  if api_key:
+    params["API_Key"] = api_key
+
+  output_path = output_dir / f"{tile}.tif"
+  if output_path.exists():
+    print(f"skip {tile}: already exists")
+    return
+
+  print(f"downloading {tile}...")
+  with httpx.stream("GET", OPENTOPOGRAPHY_URL, params=params, timeout=300.0, follow_redirects=True) as response:
+    response.raise_for_status()
+    with output_path.open("wb") as file:
+      for chunk in response.iter_bytes():
+        file.write(chunk)
+  print(f"saved {output_path}")
+
+
+def main() -> int:
+  parser = argparse.ArgumentParser(description="Download SRTM GL1 GeoTIFF tiles")
+  parser.add_argument("--bbox", nargs=4, type=float, metavar=("MIN_LAT", "MIN_LNG", "MAX_LAT", "MAX_LNG"))
+  parser.add_argument("--tiles", nargs="*", help="Explicit tile names, e.g. N59E030")
+  parser.add_argument("--output", default="data/srtm", help="Output directory")
+  parser.add_argument("--api-key", default=None, help="OpenTopography API key")
+  args = parser.parse_args()
+
+  output_dir = Path(args.output)
+  output_dir.mkdir(parents=True, exist_ok=True)
+
+  if args.tiles:
+    tiles = args.tiles
+  elif args.bbox:
+    tiles = tile_names_for_bbox(*args.bbox)
+  else:
+    parser.error("provide --bbox or --tiles")
+
+  for tile in tiles:
+    try:
+      download_tile(tile, output_dir, args.api_key)
+    except httpx.HTTPError as exc:
+      print(f"failed {tile}: {exc}", file=sys.stderr)
+
+  return 0
+
+
+if __name__ == "__main__":
+  raise SystemExit(main())