geohash.py

# -*- coding: utf8 -*-

# GeoHash decode and encode library

base32 = {
    '0': '00000',
    '1': '00001',
    '2': '00010',
    '3': '00011',
    '4': '00100',
    '5': '00101',
    '6': '00110',
    '7': '00111',
    '8': '01000',
    '9': '01001',
    'b': '01010',
    'c': '01011',
    'd': '01100',
    'e': '01101',
    'f': '01110',
    'g': '01111',
    'h': '10000',
    'j': '10001',
    'k': '10010',
    'm': '10011',
    'n': '10100',
    'p': '10101',
    'q': '10110',
    'r': '10111',
    's': '11000',
    't': '11001',
    'u': '11010',
    'v': '11011',
    'w': '11100',
    'x': '11101',
    'y': '11110',
    'z': '11111'
}

class GeoHash():
    def decode(self, geohash_str):
        # 緯度経度の範囲を求める
        def dehash(bit_array, min, max):
            for bit in bit_array:
                if bit:
                    min = (max + min) / 2.0
                else:
                    max = (max + min) / 2.0
            return (min, max)
        
        # 二進数文字列に変換する
        bit_array = []
        for str in geohash_str:
            bit_array.append(base32[str])
        
        # 偶数bitと奇数bitに分割する
        longtitude_bit_array = [] # 偶数bit
        latitude_bit_array = [] # 奇数bit
        i = 0
        for bit in bit_array:
            if i % 2 == 0:
                longtitude_bit_array.append(bit[0])
                latitude_bit_array.append(bit[1])
                longtitude_bit_array.append(bit[2])
                latitude_bit_array.append(bit[3])
                longtitude_bit_array.append(bit[4])
            else:
                latitude_bit_array.append(bit[0])
                longtitude_bit_array.append(bit[1])
                latitude_bit_array.append(bit[2])
                longtitude_bit_array.append(bit[3])
                latitude_bit_array.append(bit[4])
            i += 1
        
        latitude_bit_array = map(int, latitude_bit_array)
        longtitude_bit_array = map(int, longtitude_bit_array)
        latitude = dehash(latitude_bit_array, -90.0, 90.0)
        longtitude = dehash(longtitude_bit_array, -180.0, 180.0)
        
        return {'latitude': latitude, 'longtitude': longtitude}
    
    def encode(self, latitude, longtitude, str_len):
        # 緯度または経度の二進数文字列を求める
        def as_bit(val, bit_len, min, max):
            bit_array = []
            for i in range(bit_len):
                mid = (max + min) / 2.0
                if val > mid:
                    bit_array.append('1')
                    min = mid
                else:
                    bit_array.append('0')
                    max = mid
            return bit_array
        
        # 緯度と経度の二進数文字列を求める
        lat_len = str_len * 5 / 2
        lng_len = str_len * 5 / 2
        if str_len % 2 == 1:
            lng_len += 1
        latitude_bit_array = as_bit(latitude, lat_len, -90.0, 90.0)
        longtitude_bit_array = as_bit(longtitude, lng_len, -180.0, 180.0)
        
        # 5桁ごとにまとめる
        mixed_bit_array = []
        bit_array = []
        for i in range(str_len*5):
            if i % 2 == 0:
                mixed_bit_array.append(longtitude_bit_array.pop(0))
            else:
                mixed_bit_array.append(latitude_bit_array.pop(0))
            if (i+1) % 5 == 0:
                bit_array.append(''.join(mixed_bit_array))
                mixed_bit_array = []
        
        # Base32に変換する
        geohash_str = []
        for bit in bit_array:
            for k, v in base32.iteritems():
                if bit == v:
                    geohash_str.append(k)
        
        return ''.join(geohash_str)