Create state_lookup.py

state_lookup.py

@@ -0,0 +1,191 @@
+"""
+Derive the German Bundesland (federal state) from a lat/lon coordinate.
+
+On first use: downloads a simplified GeoJSON of German state boundaries from
+GitHub and caches it next to this file as .states_geojson_cache.json.
+Subsequent runs use the local cache (works offline).
+
+If both the cache and the download fail, get_state() returns "" and the state
+filter will simply show no options — the rest of the app keeps working normally.
+"""
+
+import os
+import json
+
+try:
+    from urllib.request import urlopen, Request
+    _HAS_URLLIB = True
+except ImportError:
+    _HAS_URLLIB = False
+
+_DIR = os.path.dirname(os.path.abspath(__file__))
+_CACHE_FILE = os.path.join(_DIR, ".states_geojson_cache.json")
+_GEOJSON_URL = (
+    "https://raw.githubusercontent.com/isellsoap/deutschlandGeoJSON/"
+    "main/2_bundeslaender/4_niedrig.geo.json"
+)
+
+_state_polygons = None  # {name: [polygons]}  polygon = [rings]  ring = [[lat, lon], ...]
+_coord_cache: dict = {}  # (lat_r, lon_r) → state_name
+
+
+# ── geometry helpers ──────────────────────────────────────────────────────────
+
+def _ray_cast(lat, lon, ring):
+    """Standard ray-casting point-in-polygon for a single ring."""
+    n = len(ring)
+    inside = False
+    j = n - 1
+    for i in range(n):
+        lat_i, lon_i = ring[i][0], ring[i][1]
+        lat_j, lon_j = ring[j][0], ring[j][1]
+        if ((lon_i > lon) != (lon_j > lon)) and \
+           (lat < (lat_j - lat_i) * (lon - lon_i) / (lon_j - lon_i) + lat_i):
+            inside = not inside
+        j = i
+    return inside
+
+
+def _in_multipolygon(lat, lon, feature_polys):
+    """
+    feature_polys: list of polygons.
+    Each polygon is a list of rings (outer first, then holes).
+    Each ring is [[lat, lon], ...].
+    """
+    for polygon in feature_polys:
+        if not polygon:
+            continue
+        if _ray_cast(lat, lon, polygon[0]):
+            if not any(_ray_cast(lat, lon, hole) for hole in polygon[1:]):
+                return True
+    return False
+
+
+# ── canonical German state names ──────────────────────────────────────────────
+
+# Maps any known variant (English, alternate spelling, abbreviation) to the
+# canonical German name used in the filter dropdown.
+_CANONICAL = {
+    # Identity (already correct)
+    "Baden-Württemberg":        "Baden-Württemberg",
+    "Bayern":                   "Bayern",
+    "Berlin":                   "Berlin",
+    "Brandenburg":              "Brandenburg",
+    "Bremen":                   "Bremen",
+    "Hamburg":                  "Hamburg",
+    "Hessen":                   "Hessen",
+    "Mecklenburg-Vorpommern":   "Mecklenburg-Vorpommern",
+    "Niedersachsen":            "Niedersachsen",
+    "Nordrhein-Westfalen":      "Nordrhein-Westfalen",
+    "Rheinland-Pfalz":          "Rheinland-Pfalz",
+    "Saarland":                 "Saarland",
+    "Sachsen":                  "Sachsen",
+    "Sachsen-Anhalt":           "Sachsen-Anhalt",
+    "Schleswig-Holstein":       "Schleswig-Holstein",
+    "Thüringen":                "Thüringen",
+    # English names (Natural Earth / some GeoJSON sources)
+    "Bavaria":                          "Bayern",
+    "Hesse":                            "Hessen",
+    "Lower Saxony":                     "Niedersachsen",
+    "Mecklenburg-Western Pomerania":    "Mecklenburg-Vorpommern",
+    "North Rhine-Westphalia":           "Nordrhein-Westfalen",
+    "Rhineland-Palatinate":             "Rheinland-Pfalz",
+    "Saxony":                           "Sachsen",
+    "Saxony-Anhalt":                    "Sachsen-Anhalt",
+    "Thuringia":                        "Thüringen",
+    # Common alternate spellings / abbreviations
+    "Baden-Wuerttemberg":       "Baden-Württemberg",
+    "Thuringen":                "Thüringen",
+    "Thueringen":               "Thüringen",
+    "Nordrhein Westfalen":      "Nordrhein-Westfalen",
+    "NRW":                      "Nordrhein-Westfalen",
+    "Mecklenburg Vorpommern":   "Mecklenburg-Vorpommern",
+    "Rheinland Pfalz":          "Rheinland-Pfalz",
+}
+
+
+def _normalise(name):
+    """Return the canonical German state name, or the original if unknown."""
+    return _CANONICAL.get(name, name)
+
+
+# ── GeoJSON loading ───────────────────────────────────────────────────────────
+
+def _parse_geojson(geojson):
+    """Convert a GeoJSON FeatureCollection to {state_name: feature_polys}."""
+    result = {}
+    for feature in geojson.get("features", []):
+        props = feature.get("properties") or {}
+        name = ""
+        for key in ("GEN", "NAME_1", "name", "NAME"):
+            if props.get(key):
+                name = _normalise(str(props[key]).strip())
+                break
+        if not name:
+            continue
+
+        geom = feature.get("geometry") or {}
+        raw_polys = []
+        if geom.get("type") == "Polygon":
+            raw_polys = [geom["coordinates"]]
+        elif geom.get("type") == "MultiPolygon":
+            raw_polys = geom["coordinates"]
+
+        # GeoJSON coordinates are [lon, lat]; convert to [lat, lon]
+        converted = []
+        for poly in raw_polys:
+            converted.append([[[pt[1], pt[0]] for pt in ring] for ring in poly])
+
+        if converted:
+            result[name] = converted
+    return result
+
+
+def _load_state_polygons():
+    global _state_polygons
+    if _state_polygons is not None:
+        return _state_polygons
+
+    geojson = None
+
+    if os.path.exists(_CACHE_FILE):
+        try:
+            with open(_CACHE_FILE, encoding="utf-8") as f:
+                geojson = json.load(f)
+        except Exception:
+            geojson = None
+
+    if geojson is None and _HAS_URLLIB:
+        try:
+            req = Request(_GEOJSON_URL, headers={"User-Agent": "StandorteMapApp/1.0"})
+            with urlopen(req, timeout=10) as resp:
+                geojson = json.loads(resp.read())
+            try:
+                with open(_CACHE_FILE, "w", encoding="utf-8") as f:
+                    json.dump(geojson, f)
+            except Exception:
+                pass
+        except Exception:
+            geojson = None
+
+    _state_polygons = _parse_geojson(geojson) if geojson else {}
+    return _state_polygons
+
+
+# ── public API ────────────────────────────────────────────────────────────────
+
+def get_state(lat, lon):
+    """Return the German Bundesland name for (lat, lon), or '' if unknown."""
+    key = (round(lat, 3), round(lon, 3))
+    if key in _coord_cache:
+        return _coord_cache[key]
+
+    polygons = _load_state_polygons()
+    result = ""
+    for name, feature_polys in polygons.items():
+        if _in_multipolygon(lat, lon, feature_polys):
+            result = name
+            break
+
+    _coord_cache[key] = result
+    return result