Module: GeoHash

Defined in:
lib/pr_geohash.rb

Overview

geohash.rb Geohash library for pure ruby Distributed under the MIT License

Based library is // github.com/davetroy/geohash-js/blob/master/geohash.js // geohash.js // Geohash library for Javascript // © 2008 David Troy // Distributed under the MIT License

Constant Summary collapse

VERSION = 
"1.0.0"
BITS = 
[0x10, 0x08, 0x04, 0x02, 0x01]
BASE32 = 
"0123456789bcdefghjkmnpqrstuvwxyz"
NEIGHBORS = 
{
  :right  => { :even => "bc01fg45238967deuvhjyznpkmstqrwx", :odd => "p0r21436x8zb9dcf5h7kjnmqesgutwvy" },
  :left   => { :even => "238967debc01fg45kmstqrwxuvhjyznp", :odd => "14365h7k9dcfesgujnmqp0r2twvyx8zb" },
  :top    => { :even => "p0r21436x8zb9dcf5h7kjnmqesgutwvy", :odd => "bc01fg45238967deuvhjyznpkmstqrwx" },
  :bottom => { :even => "14365h7k9dcfesgujnmqp0r2twvyx8zb", :odd => "238967debc01fg45kmstqrwxuvhjyznp" }
}
BORDERS = 
{
  :right  => { :even => "bcfguvyz", :odd => "prxz" },
  :left   => { :even => "0145hjnp", :odd => "028b" },
  :top    => { :even => "prxz"    , :odd => "bcfguvyz" },
  :bottom => { :even => "028b"    , :odd => "0145hjnp" }
}

Class Method Summary collapse

Class Method Details

.adjacent(geohash, dir) ⇒ Object

Calculate adjacents geohash



66
67
68
69
70
71
72
73
 
# 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

.decode(geohash) ⇒ Object

Decode from geohash

geohash

geohash code

return

decoded bounding box [[north latitude, west longitude],[south latitude, east longitude]]



22
23
24
25
26
27
28
29
30
31
32
 
# 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

.encode(latitude, longitude, precision = 12) ⇒ Object

Encode latitude and longitude into geohash



37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
 
# 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

.neighbors(geohash) ⇒ Object

Calculate neighbors (8 adjacents) geohash



56
57
58
59
60
61
 
# 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