PolylineDecoder.rb

# polyline_decoder.rb by George Lantz August 2007



# Usage Example:

#

# line = "{b~zEdruxPT?L|@PP"

# polyline_decoder = PolylineDecoder.new

# line_arr = polyline_decoder.decode(line)

#

# line_arr.each do |ln|

#   puts ln[0].to_s  + ", " + ln[1].to_s

# end



class PolylineDecoder

  

  def decode(polyline)

      encoded = polyline

      len = encoded.length

      index = 0

      array = Array.new

      lat = 0

      lng = 0

      

      while (index < len)

        shift = 0

        result = 0

        

        loop do

          a = encoded[index]

          b = a - 63

          result |= (b & 0x1f) << shift

          shift += 5

          index += 1

          break unless (b >= 0x20)

        end

        

        dlat = ((result & 1) == 1 ? ~(result >> 1) : (result >> 1))

        lat += dlat

        

        shift = 0

        result = 0

        loop do

          a = encoded[index]

          b = a - 63

          result |= (b & 0x1f) << shift

          shift += 5

          index += 1

          break unless (b >= 0x20)

        end

        

        dlng = ((result & 1) == 1 ? ~(result >> 1) : (result >> 1))

        lng += dlng

        

        array.push([lat * 1e-5, lng * 1e-5])

      end

      

      return array

  end

end