GeoHash

# File lib/pr_geohash.rb, line 66
def adjacent(geohash, dir)
  base, lastChr = geohash[0..-2], geohash[-1,1]
  type = (geohash.length % 2)==1 ? :odd : :even
  if BORDERS[dir][type].include?(lastChr)
    base = adjacent(base, dir)
  end
  base + BASE32[NEIGHBORS[dir][type].index(lastChr),1]
end

# File lib/pr_geohash.rb, line 22
def decode(geohash)
  latlng = [[-90.0, 90.0], [-180.0, 180.0]]
  is_lng = 1
  geohash.downcase.scan(/./) do |c|
    BITS.each do |mask|
      latlng[is_lng][(BASE32.index(c) & mask)==0 ? 1 : 0] = (latlng[is_lng][0] + latlng[is_lng][1]) / 2
      is_lng ^= 1
    end
  end
  latlng.transpose
end

# File lib/pr_geohash.rb, line 37
def encode(latitude, longitude, precision=12)
  latlng = [latitude, longitude]
  points = [[-90.0, 90.0], [-180.0, 180.0]]
  is_lng = 1
  (0...precision).map {
    ch = 0
    5.times do |bit|
      mid = (points[is_lng][0] + points[is_lng][1]) / 2
      points[is_lng][latlng[is_lng] > mid ? 0 : 1] = mid
      ch |=  BITS[bit] if latlng[is_lng] > mid
      is_lng ^= 1
    end
    BASE32[ch,1]
  }.join
end

# File lib/pr_geohash.rb, line 56
def neighbors(geohash)
  [[:top, :right], [:right, :bottom], [:bottom, :left], [:left, :top]].map{ |dirs|
    point = adjacent(geohash, dirs[0])
    [point, adjacent(point, dirs[1])]
  }.flatten
end