Geohashの計算ロジックの勉強

geohash_test.rb

# coding: utf-8
#
# Geohash encode/decode Test for tmp binary
# 
#

LEVEL = 8
LENGTH = LEVEL*5/2

def encode(lon, str, min, max)
  return str if str.size == LENGTH
  puts d1 = max - lon
  puts d2 = lon - min
  # ライブラリによっては、d1 == d2 の時の挙動が異なる
  if d1 < d2
    str += "1"
    min += (max - min) / 2
  else
    str += "0"
    max -= (max - min) / 2
  end
  puts "#{str},#{min},#{max}"
  return encode(lon, str, min, max)
end

def decode(arr, min, max)
  return if arr.size == 0
  puts arr.join()
  val = arr.shift
  case val 
  when "0" 
    max -= (max - min) / 2 
  when "1" 
    min += (max - min) / 2 
  else
    raise "ERROR"
  end 
  puts "#{val},#{min},#{max}"
  decode(arr, min, max)
end

lon = 138.818702697754
lat = 36.9964599609375
puts "encode test: input #{lon}"
puts encode(lon, "", min=-180.0, max=180.0)
puts "--------------------------------------------"
puts "encode test: input #{lat}"
puts encode(lat, "", min=-90.0, max=90.0)
puts "--------------------------------------------"

# 以下は上記緯度経度のencode後の文字列
lon = "11100010101101110010"
lat = "10110100100111100000"
puts "decode test input: #{lon}"
decode(lon.split(""), min=-180.0, max=180.0)
puts "--------------------------------------------"
puts "decode test input: #{lat}"
decode(lat.split(""), min=-90.0, max=90.0)