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NMEA output

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  • wallsofjasper2
    All, I just dl ed AISMON and would like to see the messages that it outputs. I checked the log file and i see garbled stuff inside the log. The program tells
    Message 1 of 14 , Aug 1, 2005
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      All,
      I just dl'ed AISMON and would like to see the messages that it
      outputs. I checked the log file and i see garbled stuff inside the
      log. The program tells me that i am getting positive decodes and no
      errors..
      Any clues to why the log looks garbled (i.e. not man readable) Thanks!

      Jim
    • Dave Houy
      Jim, ... The logfile records should all begin with !AIVDM, but consist of mostly- encoded data thereafter. Are you seeing something different? Dave
      Message 2 of 14 , Aug 1, 2005
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        Jim,

        > I just dl'ed AISMON and would like to see the messages that it
        > outputs. I checked the log file and i see garbled stuff inside the
        > log. The program tells me that i am getting positive decodes and no
        > errors..
        > Any clues to why the log looks garbled (i.e. not man readable) Thanks!

        The logfile records should all begin with !AIVDM, but consist of mostly-
        encoded data thereafter. Are you seeing something different?

        Dave
      • wallsofjasper2
        ... Yes, That is what i am seeing. Why is it encrypted? Is there a way to decipher the printout?
        Message 3 of 14 , Aug 1, 2005
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          --- In aismon@yahoogroups.com, "Dave Houy" <davehouy@p...> wrote:
          > Jim,
          >
          > > I just dl'ed AISMON and would like to see the messages that it
          > > outputs. I checked the log file and i see garbled stuff inside the
          > > log. The program tells me that i am getting positive decodes and no
          > > errors..
          > > Any clues to why the log looks garbled (i.e. not man readable) Thanks!
          >
          > The logfile records should all begin with !AIVDM, but consist of mostly-
          > encoded data thereafter. Are you seeing something different?
          >
          > Dave


          Yes, That is what i am seeing. Why is it encrypted? Is there a way to
          decipher the printout?
        • Dave Houy
          Jim, ... When creating AIVDM messages, it is required to encode each 6 bits of the received stream into an 8-bit byte in the output message in order to avoid
          Message 4 of 14 , Aug 1, 2005
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            Jim,

            > Yes, That is what i am seeing. Why is it encrypted? Is there a way to
            > decipher the printout?

            When creating AIVDM messages, it is required to encode each 6 bits of
            the received stream into an 8-bit byte in the output message in order
            to avoid non-printable characters.

            Dave
          • wallsofjasper2
            ... So how do i translate that then? What NMEA format are you using? I am trying to use AISMon to bring in man-readable reports so I can plot them. Thanks! :)
            Message 5 of 14 , Aug 2, 2005
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              --- In aismon@yahoogroups.com, "Dave Houy" <davehouy@p...> wrote:
              > Jim,
              >
              > > Yes, That is what i am seeing. Why is it encrypted? Is there a way to
              > > decipher the printout?
              >
              > When creating AIVDM messages, it is required to encode each 6 bits of
              > the received stream into an 8-bit byte in the output message in order
              > to avoid non-printable characters.
              >
              > Dave

              So how do i translate that then? What NMEA format are you using?
              I am trying to use AISMon to bring in man-readable reports so I can
              plot them. Thanks! :)

              Jim
            • Dave Houy
              Jim, ... AISMon currently produces NMEA output for AIS message types 1-3 and 5. The next version will also support Class B types 18 and 19. To reconstitute
              Message 6 of 14 , Aug 2, 2005
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                Jim,

                > So how do i translate that then?

                AISMon currently produces NMEA output for AIS message types 1-3 and
                5. The next version will also support Class B types 18 and 19.

                To reconstitute the original AIS bitstream, for each encoded NMEA
                byte:

                x=byte
                if x >= 95 then
                x = x - 56
                else
                x = x - 48
                endif

                The low-order six bits of x are the original AIS bits.

                Dave
              • wallsofjasper2
                ... Could you provide an example of how you decoded this? for example: !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B
                Message 7 of 14 , Aug 2, 2005
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                  --- In aismon@yahoogroups.com, "Dave Houy" <davehouy@p...> wrote:
                  > Jim,
                  >
                  > > So how do i translate that then?
                  >
                  > AISMon currently produces NMEA output for AIS message types 1-3 and
                  > 5. The next version will also support Class B types 18 and 19.
                  >
                  > To reconstitute the original AIS bitstream, for each encoded NMEA
                  > byte:
                  >
                  > x=byte
                  > if x >= 95 then
                  > x = x - 56
                  > else
                  > x = x - 48
                  > endif
                  >
                  > The low-order six bits of x are the original AIS bits.
                  >
                  > Dave

                  Could you provide an example of how you decoded this? for example:

                  !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B
                • Dave Houy
                  Jim, ... Firstly, I did not decode this message, I encoded it from the decoded AIS bitstream. Put these 28 bytes 13uTAH002nJRLAHEwTi674rh04:8 through the
                  Message 8 of 14 , Aug 2, 2005
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                    Jim,

                    > Could you provide an example of how you decoded this? for example:
                    >
                    > !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B

                    Firstly, I did not decode this message, I encoded it from the decoded
                    AIS bitstream.

                    Put these 28 bytes 13uTAH002nJRLAHEwTi674rh04:8 through the provided
                    decoding routine, and the accumulated returned 168 (i.e. 28 * 6) bits
                    represent the original AIS message. AIS message formats are documented
                    in ITU-R M.1371-1, available at www.itu.int.

                    Dave
                  • Jim Wyman
                    Thanks! I will try this tomorrow...
                    Message 9 of 14 , Aug 2, 2005
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                      Thanks! I will try this tomorrow...

                      Dave Houy wrote:
                      Jim,

                      > Could you provide an example of how you decoded this? for example:
                      >
                      > !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B

                      Firstly, I did not decode this message, I encoded it from the decoded
                      AIS bitstream.

                      Put these 28 bytes 13uTAH002nJRLAHEwTi674rh04:8 through the provided
                      decoding routine, and the accumulated returned 168 (i.e. 28 * 6) bits
                      represent the original AIS message.  AIS message formats are documented
                      in ITU-R M.1371-1, available at www.itu.int.

                      Dave


                    • wallsofjasper2
                      Dave, Thanks for all the help. That algorithm did the trick... One thing though.. On message type 5 (static ship/voyage data), there are so-called normal 6-bit
                      Message 10 of 14 , Aug 3, 2005
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                        Dave,
                        Thanks for all the help. That algorithm did the trick... One thing
                        though.. On message type 5 (static ship/voyage data), there are
                        so-called normal 6-bit ascii fields for the call sign. This is a 7
                        character long field. What do I use do convert the 6-bit values into a
                        man-readable character. Is their ASCII table for 6-bit values?

                        --- In aismon@yahoogroups.com, Jim Wyman <jwyman@g...> wrote:
                        > Thanks! I will try this tomorrow...
                        >
                        > Dave Houy wrote:
                        >
                        > > Jim,
                        > >
                        > > > Could you provide an example of how you decoded this? for example:
                        > > >
                        > > > !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B
                        > >
                        > > Firstly, I did not decode this message, I encoded it from the decoded
                        > > AIS bitstream.
                        > >
                        > > Put these 28 bytes 13uTAH002nJRLAHEwTi674rh04:8 through the provided
                        > > decoding routine, and the accumulated returned 168 (i.e. 28 * 6) bits
                        > > represent the original AIS message. AIS message formats are
                        documented
                        > > in ITU-R M.1371-1, available at www.itu.int.
                        > >
                        > > Dave
                        > >
                        > >
                        > >
                        > >
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                      • Dave Houy
                        Jim, ... See Table 14 on page 42 of ITU-R M.1371-1. Dave
                        Message 11 of 14 , Aug 3, 2005
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                          Jim,

                          > What do I use do convert the 6-bit values into a
                          > man-readable character. Is their ASCII table for
                          > 6-bit values?

                          See Table 14 on page 42 of ITU-R M.1371-1.

                          Dave
                        • wallsofjasper2
                          Dave, I do not have that document. I am looking at the IALA Technical Clarifications on ITU Recommendations ITU-R M.1371-1 Edition 1.4 2003 for all the message
                          Message 12 of 14 , Aug 3, 2005
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                            Dave,
                            I do not have that document. I am looking at the IALA Technical
                            Clarifications on ITU Recommendations ITU-R M.1371-1 Edition 1.4 2003
                            for all the message formats.

                            Jim




                            --- In aismon@yahoogroups.com, "Dave Houy" <davehouy@p...> wrote:
                            > Jim,
                            >
                            > > What do I use do convert the 6-bit values into a
                            > > man-readable character. Is their ASCII table for
                            > > 6-bit values?
                            >
                            > See Table 14 on page 42 of ITU-R M.1371-1.
                            >
                            > Dave
                          • Dave Houy
                            Jim, ... Then download it from www.itu.int, as I have done. Dave
                            Message 13 of 14 , Aug 4, 2005
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                              Jim,

                              > I do not have that document.

                              Then download it from www.itu.int, as I have done.

                              Dave
                            • m_halterman
                              Jim, I have been working on a decoder function to no avail. Would you be willing to post the code you came up with to decode the AIS message? Thanks, Mike ...
                              Message 14 of 14 , Aug 7, 2006
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                                Jim, I have been working on a decoder function to no avail. Would
                                you be willing to post the code you came up with to decode the AIS
                                message?

                                Thanks,

                                Mike

                                --- In aismon@yahoogroups.com, "wallsofjasper2" <jwyman@...> wrote:
                                >
                                > Dave,
                                > Thanks for all the help. That algorithm did the trick... One thing
                                > though.. On message type 5 (static ship/voyage data), there are
                                > so-called normal 6-bit ascii fields for the call sign. This is a 7
                                > character long field. What do I use do convert the 6-bit values
                                into a
                                > man-readable character. Is their ASCII table for 6-bit values?
                                >
                                > --- In aismon@yahoogroups.com, Jim Wyman <jwyman@g...> wrote:
                                > > Thanks! I will try this tomorrow...
                                > >
                                > > Dave Houy wrote:
                                > >
                                > > > Jim,
                                > > >
                                > > > > Could you provide an example of how you decoded this? for
                                example:
                                > > > >
                                > > > > !AIVDM,1,1,,A,13uTAH002nJRLAHEwTi674rh04:8,0*2B
                                > > >
                                > > > Firstly, I did not decode this message, I encoded it from the
                                decoded
                                > > > AIS bitstream.
                                > > >
                                > > > Put these 28 bytes 13uTAH002nJRLAHEwTi674rh04:8 through the
                                provided
                                > > > decoding routine, and the accumulated returned 168 (i.e. 28 *
                                6) bits
                                > > > represent the original AIS message. AIS message formats are
                                > documented
                                > > > in ITU-R M.1371-1, available at www.itu.int.
                                > > >
                                > > > Dave
                                > > >
                                > > >
                                > > >
                                > > >
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