解决geohash编码跨区域问题

在上一篇文章中提出用geohash解决匹配点的性能问题，该算法有个缺陷也就是如果在边界上的时候，该点附近的点可能就跨界了，也就是通过该点的geohash值无法找到对应的点。例如：
解决geohash编码跨区域问题
图中蓝色点为需要绑路映射的点
下方的红点为绑路计算之后的点
导致偏移的原因是
随州街上的点数据在geohashcode分区时都属于蓝点上方的分区
在数据库中查询出来的结果显示和蓝色点在一个分区的路网数据位于下图
解决geohash编码跨区域问题
所以找到的数据均位于下方的道路上导致偏移问题
为了解决这个问题提出扩散hashcode的代码查找附近范围的geohashcode代码
代码如下
所以找到的数据均位于下方的道路上导致偏移问题
为了解决这个问题提出扩散hashcode的代码查找附近范围的geohashcode代码
代码如下

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"""A simple GeoHash implementation."""`

# Forward and reverse base 32 map
BASESEQUENCE = '0123456789bcdefghjkmnpqrstuvwxyz'
BASE32MAP = dict((k, count) for count, k in enumerate(BASESEQUENCE))
BASE32MAPR = dict((count, k) for count, k in enumerate(BASESEQUENCE))

def _bits_to_float(bits, lower=-90.0, middle=0.0, upper=90.0):
    """Convert GeoHash bits to a float."""
    for i in bits:
        if i:
            lower = middle
        else:
            upper = middle
        middle = (upper + lower) / 2
    return middle

def _float_to_bits(value, lower=-90.0, middle=0.0, upper=90.0, length=15):
    """Convert a float to a list of GeoHash bits."""
    ret = []
    for i in range(length):
        if value >= middle:
            lower = middle
            ret.append(1)
        else:
            upper = middle
            ret.append(0)
        middle = (upper + lower) / 2
    return ret

def _geohash_to_bits(value):
    """Convert a GeoHash to a list of GeoHash bits."""
    b = map(BASE32MAP.get, value)
    ret = []
    for i in b:
        out = []
        for z in range(5):
            out.append(i & 0b1)
            i = i >> 1
        ret += out[::-1]
    return ret

def _bits_to_geohash(value):
    """Convert a list of GeoHash bits to a GeoHash."""
    ret = []
    # Get 5 bits at a time
    for i in (value[i:i + 5] for i in range(0, len(value), 5)):
        # Convert binary to integer
        # Note: reverse here, the slice above doesn't work quite right in reverse.
        total = sum([(bit * 2 ** count) for count, bit in enumerate(i[::-1])])
        ret.append(BASE32MAPR[total])
    # Join the string and return
    return "".join(ret)

# Public
def decode(value):
    """Decode a geohash. Returns a (lon,lat) pair."""
    assert value, "Invalid geohash: %s" % value
    # Get the GeoHash bits
    bits = _geohash_to_bits(value)
    # Unzip the GeoHash bits.
    lon = bits[0::2]
    lat = bits[1::2]
    # Convert to lat/lon
    return (
        _bits_to_float(lon, lower=-180.0, upper=180.0),
        _bits_to_float(lat)
    )

def encode(lonlat, length=12):
    """Encode a (lon,lat) pair to a GeoHash."""
    assert len(lonlat) == 2, "Invalid lon/lat: %s" % lonlat
    # Half the length for each component.
    length /= 2
    lon = _float_to_bits(lonlat[0], lower=-180.0, upper=180.0, length=length * 5)
    lat = _float_to_bits(lonlat[1], lower=-90.0, upper=90.0, length=length * 5)
    # Zip the GeoHash bits.
    ret = []
    for a, b in zip(lon, lat):
        ret.append(a)
        ret.append(b)
    return _bits_to_geohash(ret)

def adjacent(geohash, direction):
    """Return the adjacent geohash for a given direction."""
    # Based on an MIT licensed implementation by Chris Veness from:
    #   http://www.movable-type.co.uk/scripts/geohash.html
    assert direction in 'nsew', "Invalid direction: %s" % direction
    assert geohash, "Invalid geohash: %s" % geohash
    neighbor = {
        'n': ['p0r21436x8zb9dcf5h7kjnmqesgutwvy', 'bc01fg45238967deuvhjyznpkmstqrwx'],
        's': ['14365h7k9dcfesgujnmqp0r2twvyx8zb', '238967debc01fg45kmstqrwxuvhjyznp'],
        'e': ['bc01fg45238967deuvhjyznpkmstqrwx', 'p0r21436x8zb9dcf5h7kjnmqesgutwvy'],
        'w': ['238967debc01fg45kmstqrwxuvhjyznp', '14365h7k9dcfesgujnmqp0r2twvyx8zb']
    }
    border = {
        'n': ['prxz', 'bcfguvyz'],
        's': ['028b', '0145hjnp'],
        'e': ['bcfguvyz', 'prxz'],
        'w': ['0145hjnp', '028b']
    }
    last = geohash[-1]
    parent = geohash[0:-1]
    t = len(geohash) % 2
    # Check for edge cases
    if (last in border[direction][t]) and (parent):
        parent = adjacent(parent, direction)
    return parent + BASESEQUENCE[neighbor[direction][t].index(last)]

def neighbors(geohash):
    """Return all neighboring geohashes."""
    return {
        'n': adjacent(geohash, 'n'),
        'ne': adjacent(adjacent(geohash, 'n'), 'e'),
        'e': adjacent(geohash, 'e'),
        'se': adjacent(adjacent(geohash, 's'), 'e'),
        's': adjacent(geohash, 's'),
        'sw': adjacent(adjacent(geohash, 's'), 'w'),
        'w': adjacent(geohash, 'w'),
        'nw': adjacent(adjacent(geohash, 'n'), 'w'),
        'c': geohash
    }

def neighborsfit(centroid, points):
    centroid = encode(centroid)
    points = map(encode, points)
    for i in range(1, len(centroid)):
        g = centroid[0:i]
        n = set(neighbors(g).values())
        unbounded = [point for point in points if (point[0:i] not in n)]
        if unbounded:
            break
    return g[0:-1]

本文标题：解决geohash编码跨区域问题
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