#!/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 pi, atan, sinh, degrees, pow as math_pow


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))))