extract POIs from a TomTom *.ov2 file (in Ruby)

binary_file_string_utils.rb

module BinaryFileStringUtils
 def byte_to_int
   self.unpack('U').first
 end

 def little_endian_to_int
   # source : http://stackoverflow.com/questions/5236059/unpack-signed-little-endian-in-ruby
   arr, bits, num = self.unpack('V*'), 0, 0
   arr.each do |int|
     num += int << bits
     bits += 32
   end
   num >= 2**(bits-1) ? num - 2**bits : num  # Convert from unsigned to signed
 end
end
String.send :include, BinaryFileStringUtils

main.rb

path = File.absolute_path File.join File.dirname($FILENAME), '..', 'data/poi/Amis.ov2'

File.open(path, 'rb') do |file|
  @pois = POI::Reader.new(file).extract_pois
end
puts @pois

#<struct POI type=2, x=4.12345, y=50.1234, text="Al">
#<struct POI type=2, x=4.23456, y=50.5678, text="Bob">
#<struct POI type=2, x=4.34567, y=50.9012, text="Carl">

poi.rb

class POI < Struct.new(:type, :x, :y, :text)
end

poi_reader.rb

class POI
  class Reader
    attr_reader :file
    def initialize(file)
      @file = file
      file.extend POIFileReadingUtils
    end

    def extract_pois
      pois = []
      begin
        poi = extract_poi
        pois << poi if poi
      end until file.eof?
      pois
    end

  private

    def extract_poi
      raw_type = file.read(1)
      type = raw_type.byte_to_int rescue raw_type

      case type
        when 0  then skip_type_0_poi
        when 2  then extract_type_2_poi
        when 1, 3
          raise "Not Implemented type : #{type.inspect}"
        else
          raise "Invalid type : #{type.inspect}"
      end
    end

    def skip_type_0_poi
      len   = file.read_poi_record_len
      rest  = file.read(len - (1+4))
      nil
    end

    def extract_type_2_poi
      len   = file.read_poi_record_len
      x     = file.read_poi_x_coordinate
      y     = file.read_poi_y_coordinate
      text  = file.read_poi_text(len - (1+4+4+4))
      POI.new(2, x, y, text)
    end
  end

private
  module POIFileReadingUtils
    def read_poi_text(len)
      read(len).chomp("\u0000")
    end
    def read_poi_record_len
      read(4).little_endian_to_int
    end
    def read_poi_x_coordinate
      read(4).little_endian_to_int/100_000.0
    end
    alias read_poi_y_coordinate read_poi_x_coordinate
  end


end