def calc_transfers(conn, threshold_meters=1000):
geohash_precision = _get_geo_hash_precision(threshold_meters / 1000.)
geo_index = GeoGridIndex(precision=geohash_precision)
g = GTFS(conn)
stops = g.get_table("stops")
stop_geopoints = []
cursor = conn.cursor()
for stop in stops.itertuples():
stop_geopoint = GeoPoint(stop.lat, stop.lon, ref=stop.stop_I)
geo_index.add_point(stop_geopoint)
stop_geopoints.append(stop_geopoint)
for stop_geopoint in stop_geopoints:
nearby_stop_geopoints = geo_index.get_nearest_points_dirty(
stop_geopoint, threshold_meters / 1000.0, "km")
from_stop_I = int(stop_geopoint.ref)
from_lat = stop_geopoint.latitude
from_lon = stop_geopoint.longitude
to_stop_Is = []
distances = []
for nearby_stop_geopoint in nearby_stop_geopoints:
to_stop_I = int(nearby_stop_geopoint.ref)
if to_stop_I == from_stop_I:
continue
to_lat = nearby_stop_geopoint.latitude
to_lon = nearby_stop_geopoint.longitude
distance = math.ceil(
wgs84_distance(from_lat, from_lon, to_lat, to_lon))
if distance <= threshold_meters:
to_stop_Is.append(to_stop_I)
distances.append(distance)
n_pairs = len(to_stop_Is)
from_stop_Is = [from_stop_I] * n_pairs
cursor.executemany(
'INSERT OR REPLACE INTO stop_distances VALUES (?, ?, ?, ?, ?, ?);',
zip(from_stop_Is, to_stop_Is, distances, [None] * n_pairs,
[None] * n_pairs, [None] * n_pairs))
cursor.execute(
'CREATE INDEX IF NOT EXISTS idx_sd_fsid ON stop_distances (from_stop_I);'
)
