ads_frequency.rb

module ADS_B
    class Decoder
        def parse_segment_msg(msg)
            return msg.to_s(2)[0..4], 
                   msg.to_s(2)[5..7], 
                   msg.to_s(2)[8..31], 
                   msg.to_s(2)[32..87], 
                   msg.to_s(2)[88..111]
        end

=begin
        ///////////////////////////////
        //// Identification trame ////
        ////////////////////////////
=end
        def parse_me_trame_identification_aircraft(me)
            return me[0..4], me[5..7], 
                    [me[8..13], me[14..19], 
                    me[20..25], me[26..31], 
                    me[32..37], me[38..43], 
                    me[44..49], me[50..55]] 
        end

        def is_identification_tc(me)
            return true if me[0..4].to_i(2) <= 4 && me[0..4].to_i(2) >= 1
        end

        def decode_icao_value(identification_trame_me)
            tc, ca, c = parse_me_trame_identification_aircraft(identification_trame_me)
            if(is_identification_tc(identification_trame_me))
                c.map.with_index do |char, i|
                    if(char.to_i(2) >= 1 && char.to_i(2) <= 26)
                        c[i] = ((char.to_i(2)-1 & 31) + 65).chr
                    else
                        c[i] = (char.to_i(2) != 32 ? char.to_i(2).chr : "_")
                    end
                end
                return true, tc.to_i(2), ca.to_i(2), c.join
            else
                return "NOT_VALID_IDENTIFICATION_AIRCRAFT_ME", nil, nil, nil
            end
        end
=begin
        ///////////////////////////////////
        //// End Identification trame ////
        /////////////////////////////////
=end 


=begin
        ///////////////////////////////
        ////   Position trame    ////
        ////////////////////////////
=end

        def parse_position_me_trame(me_trame)
            return me_trame[0..4],me_trame[5..6], 
                   me_trame[7], me_trame[8..19], 
                   me_trame[20], me_trame[21],
                   me_trame[22..38], me_trame[39..55]
        end

        def mod(x, y)
            return x-y*((x/y).floor)
        end

        def nl(lat)
            return ((2*Math::PI)/(Math.acos(1-((1-Math.cos(Math::PI/(2*15)))/(Math.cos((Math::PI/180)*lat)**2))))).floor
        end

        def global_unambiguous_position(me1, me2)
            tc1, ss1, saf1, alt1, t1, f1, lat_pcr1, long_pcr1 = self.parse_position_me_trame(me1)
            tc2, ss2, saf2, alt2, t2, f2, lat_pcr2, long_pcr2 = self.parse_position_me_trame(me2)
            #calculate hint of lat
            j = (59*lat_pcr1.to_i(2)/2**17-60*lat_pcr2.to_i(2)/2**17+1/2).floor
            #decode lat even
            lat_even = (360/60.to_f)*((j%60)+lat_pcr1.to_i(2)/(2**17).to_f)
            lat_odd = (360/59.to_f)*((j%59)+lat_pcr2.to_i(2)/(2**17).to_f)
            lat = lat_even
            if(nl(lat) == nl(lat_odd))
                m = (long_pcr1.to_i(2)/2**17*(nl(lat)-1)-long_pcr2.to_i(2)/2**17*nl(lat)+1/2).floor
                n = [nl(lat), 1].max
                long = (360/n.to_f)*((m%n)+long_pcr1.to_i(2)/(2**17).to_f)
                return lat, long
            end
        end

        def decode_position_globally(trame_even, trame_odd)
            df_even, ca_even, icao_even, me_even, pi_even = self.parse_segment_msg(trame_even)
            df_odd, ca_odd, icao_odd, me_odd, pi_odd = self.parse_segment_msg(trame_odd)

            return global_unambiguous_position(me_even, me_odd)
        end


        def decode_locally_unambiguous_position(trame, lat_ref, long_ref)
            tc1, ss1, saf1, alt1, t1, f1, lat_pcr1, long_pcr1 = self.parse_position_me_trame(trame.to_s(2))
            dLat = (360/60)
            #Equation to get latitude zone index
            j = (lat_ref/dLat).floor + (((lat_ref%dLat)/dLat)-(lat_pcr1.to_i(2)/2**17)+(1/2)).floor
            lat = dLat*(j+(lat_pcr1.to_i(2)/2**17))
            puts lat
        end



=begin
        ///////////////////////////////
        ////  End Position trame  ////
        ////////////////////////////
=end

        def decode(msg)
            if(msg.to_s(2).length == 112)
                df, ca, icao, me, pi = self.parse_segment_msg(msg)
                if(self.is_identification_tc(me))
                    return (error, tc, ca, name = self.decode_icao_value(me))
                end
            else
                return "NOT_VALID_LENGTH_TRAME", nil
            end
        end
    end
end


dec = ADS_B::Decoder.new
dec.decode_locally_unambiguous_position(0x8D40621D58C382D690C8AC2863A7, 52.258, 3.918)