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#!/usr/bin/env python
# -------------------------------------------------------
# Translates between lat/long and the slippy-map tile
# numbering scheme
#
# http://wiki.openstreetmap.org/index.php/Slippy_map_tilenames
#
# Written by Oliver White, 2007
# This file is public-domain
# -------------------------------------------------------
from math import atan, degrees, pi
from math import pow as math_pow
from math import sinh
def num_tiles(z):
return math_pow(2, z)
def lat_edges(y, z):
n = num_tiles(z)
unit = 1 / n
relY1 = y * unit
relY2 = relY1 + unit
lat1 = mercator_to_lat(pi * (1 - 2 * relY1))
lat2 = mercator_to_lat(pi * (1 - 2 * relY2))
return (lat1, lat2)
def lon_edges(x, z):
n = num_tiles(z)
unit = 360 / n
lon1 = -180 + x * unit
lon2 = lon1 + unit
return (lon1, lon2)
def tile_edges(x, y, z):
lat1, lat2 = lat_edges(y, z)
lon1, lon2 = lon_edges(x, z)
return (lon1, lat2, lon2, lat1) # w, s, e, n
def mercator_to_lat(mercatorY):
return degrees(atan(sinh(mercatorY)))
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