pygeohash.py

import numpy as np
from math import log10

__base32 = '0123456789bcdefghjkmnpqrstuvwxyz'
__decodemap = dict()
for i in range(len(__base32)):
    __decodemap[__base32[i]] = i

def decode_exactly(geohash):
    """
    Decode the geohash to its exact values, including the error
    margins of the result.  Returns four float values: latitude,
    longitude, the plus/minus error for latitude (as a positive
    number) and the plus/minus error for longitude (as a positive
    number).
    """

    lat_interval, lon_interval = (-90.0, 90.0), (-180.0, 180.0)
    lat_err, lon_err = 90.0, 180.0
    is_even = True
    for c in geohash:
        cd = __decodemap[c]
        for mask in [16, 8, 4, 2, 1]:
            if is_even:  # adds longitude info
                lon_err /= 2
                if cd & mask:
                    lon_interval = ((lon_interval[0] + lon_interval[1]) / 2,
                                    lon_interval[1])
                else:
                    lon_interval = (lon_interval[0],
                                    (lon_interval[0] + lon_interval[1]) / 2)
            else:  # adds latitude info
                lat_err /= 2
                if cd & mask:
                    lat_interval = ((lat_interval[0] + lat_interval[1]) / 2,
                                    lat_interval[1])
                else:
                    lat_interval = (lat_interval[0],
                                    (lat_interval[0] + lat_interval[1]) / 2)
            is_even = not is_even
    lat = (lat_interval[0] + lat_interval[1]) / 2
    lon = (lon_interval[0] + lon_interval[1]) / 2
    return lat, lon, lat_err, lon_err


def point_decode(geohash):
    """
    Decode geohash, returning two float with latitude and longitude
    containing only relevant digits and with trailing zeroes removed.
    """
    lat, lon, lat_err, lon_err = decode_exactly(geohash)
    # Format to the number of decimals that are known
    lats = "%.*f" % (max(1, int(round(-log10(lat_err)))) - 1, lat)
    lons = "%.*f" % (max(1, int(round(-log10(lon_err)))) - 1, lon)
    if '.' in lats: lats = lats.rstrip('0')
    if '.' in lons: lons = lons.rstrip('0')
    return float(lats), float(lons)

def point_encode(latitude, longitude, precision=12):
    """
    Encode a position given in float arguments latitude, longitude to
    a geohash which will have the character count precision.
    """
    lat_interval = (-90.0, 90.0)
    lon_interval = (-180.0, 180.0)
    geohash = []
    bits = [16, 8, 4, 2, 1]
    bit = 0
    ch = 0
    even = True
    while len(geohash) < precision:
        if even:
            mid = (lon_interval[0] + lon_interval[1]) / 2
            if longitude > mid:
                ch |= bits[bit]
                lon_interval = (mid, lon_interval[1])
            else:
                lon_interval = (lon_interval[0], mid)
        else:
            mid = (lat_interval[0] + lat_interval[1]) / 2
            if latitude > mid:
                ch |= bits[bit]
                lat_interval = (mid, lat_interval[1])
            else:
                lat_interval = (lat_interval[0], mid)
        even = not even
        if bit < 4:
            bit += 1
        else:
            geohash += __base32[ch]
            bit = 0
            ch = 0
    return ''.join(geohash)