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Diffstat (limited to 'www/AIVDM.txt')
| -rw-r--r-- | www/AIVDM.txt | 72 |
1 files changed, 56 insertions, 16 deletions
diff --git a/www/AIVDM.txt b/www/AIVDM.txt index 383ef9ae..0dfe589c 100644 --- a/www/AIVDM.txt +++ b/www/AIVDM.txt @@ -51,19 +51,20 @@ technically difficult and impeded by legal barriers. ITU Recommendation M.1371, "Technical Characteristics for a Universal Shipborne Automatic Identification System Using Time Division Multiple -Access" <<ITU1371>>, issued in 2001, describes the bit-level format of -AIS radio messages. This standard was proprietary and expensive for -a long time. It became available for free download, apparently at -some point in 2011, well after most of ths document was assembled. +Access" <<ITU1371>>, issued in 2001, first described the bit-level +format of AIS radio messages. This standard was proprietary and +expensive. I did not have access to it or any of its followup +revisions while assembling versions of this document up to 1.29. -ITU-R M.1371 is expanded and clarified by "IALA Technical +ITU-R M.1371 was expanded and clarified by "IALA Technical Clarifications on Recommendation ITU-R M.1371-1" <<IALA>>, which is freely available. -There have been two minor revisions of ITU-R M.1371 since it was +There have been three minor revisions of ITU-R M.1371 since it was originally issued. These add interpretations to packet bitfields that -were previously marked "spare" and "regional reserved". I have not -seen these either, but have been passed information on them. +were previously marked "spare" and "regional reserved". ITU-R M.1371 +revision 4 became available for free download, apparently at some +point in early 2011, well after most of this document was assembled. The ASCII format for AIVDM/AIVDO representations of AIS radio messages seems to have been set by IEC-PAS 61162-100, "Maritime navigation and @@ -96,6 +97,8 @@ ITU-1371-3. Descriptions of messages 25 and 26 are based on AIS transceiver vendor documentation forwarded to me by a source wishing to remain anonymous. +Message type 27 was described in ITU1371-4 and added here after that +became a freely available download. Should you set out to write a decoder using this document, you are likely to find that one of your challenges is finding enough AIS @@ -130,7 +133,7 @@ relevant proprietary standards. If you are such a person, please help by reporting the following to be included in future versions of this document: -* Sample sentences of types 16-17, 22-23, and 25-26. +* Sample sentences of types 16-17, 22-23, and 25-27. * Sample sentences of type 6 and 8 conforming to <<IMO236>> and <<IMO289>>. @@ -418,6 +421,7 @@ types are as follows: |24 |Class B CS Static Data Report |25 |Binary Message, Single Slot |26 |Binary Message, Multiple Slot +|27 |Position report for long-range applications |====================================================== In normal operation, an AIS transceiver will broadcast a position report @@ -458,7 +462,7 @@ are derived from <<IALA>>. Message type 23 was decribed to me by Mike Greene based on <<IEC-62287>>. Message type 24 was described to me by <<Schwehr>>, whose Python toolkit decodes it. Message types 25-26 are reported by <<Schwehr>>, who observes they were added in Version 3 of -<<ITU1371>>. +<<ITU1371>>. Message type 27 is direct from <<ITU1371>> version 4. The "Member" column in these tables is not derived from any of the ITU standards or amendments. I have invented it in order to be able to @@ -471,7 +475,7 @@ set to use. The field breakdowns in this document have been checked against live decoded data rendered by known-good implementations for message types 1-15, 18-21, and 24. Described but unchecked are 16-17, 22-23, and -25-26. Also, the interpretation of IMO extension subtypes of messages +25-27. Also, the interpretation of IMO extension subtypes of messages 6 and 8 has yet to be tested. Bit lengths and length ranges are given because decoders should check @@ -559,7 +563,7 @@ Speed over ground is in 0.1-knot resolution from 0 to 102 knots. value 1023 indicates speed is not available, value 1022 indicates 102.2 knots or higher. -Position accuracy flag indicates the accuracy of the fix. A value of +The position accuracy flag indicates the accuracy of the fix. A value of 1 indicates a DGPS-quality fix with an accuracy of < 10ms. 0, the default, indicates an unaugmented GNSS fix with accuracy > 10m. @@ -2167,8 +2171,10 @@ than 9, and (c) end padding changes from 6 to 10 bits. |38-39 | 2 |Spare | |Not used |40-55 | 16 |DAC/FID | |DAC = 001 FID = 11 |56-80 | 25 |Longitude |lon |Signed: unit minutes * 0.001 +| | | | |East positive, West negative | | | | |181000 = N/A (default) |81-104 | 24 |Latitude |lat |Signed: unit minutes * 0.001 +| | | | |North positive, South negative | | | | |91000 = N/A (default) |105-105 | 1 |Fix quality |accuracy |As in Common Navigation Block |106-110 | 5 |Day |day |1-31, 0=N/A (default) @@ -2932,7 +2938,7 @@ Takes up 60-1064 bits (up to 5 slots). [frame="topbot",options="header"] |============================================================================== |Field |Len |Description | Member | Units -|0-5 | 6 | Message Type | type | Unsigned integer: 25 +|0-5 | 6 | Message Type | type | Unsigned integer: 26 |6-7 | 2 | Repeat Indicator | repeat | As in CNB |8-37 | 30 | MMSI | mmsi | Unsigned integer: 9 digits |38 | 1 | Destination indicator| addressed | 0=broadcast,1=addressed @@ -2957,6 +2963,39 @@ whether it should be interpretred as a SOTDMA or ITDMA state. Note: Type 26 is extremely rare. As of March 2010 it has not been observed even in long-duration samples from AISHub. +=== Type 27: Long Range AIS Broadcast message === + +ITU-1371-4 says this message is primarily intended for long-range +detection of AIS Class A equipped vessels (typically by +satellite). This message has a similar content to Messages 1, 2 and 3, +but the total number of bits has been compressed to allow for +increased propagation delays associated with long-range detection + +[frame="topbot",options="header"] +|============================================================================== +|Field |Len |Description |Member |Units +|0-5 | 6 |Message Type |type |Unsigned integer: 27 +|6-7 | 2 |Repeat Indicator |repeat |As in CNB +|8-37 | 30 |MMSI |mmsi |Unsigned integer: 9 digits +|38-38 | 1 |Position Accuracy |accuracy |See Common Navigation Block +|39-39 | 1 |RAIM flag |raim |See Common Navigation Block +|40-43 | 4 |Navigation Status |status |See Common Navigation Block +|44-61 | 18 |Longitude |lon |Signed: minutes/10 +| | | | |East positive, West negative +| | | | |181000 = N/A (default) +|62-78 | 17 |Latitude |lat |Signed: minutes/10 +| | | | |North positive, South negative +| | | | |91000 = N/A (default) +|79-84 | 6 |Speed Over Ground |speed |Knots (0-62); 63 = N/A (default) +|85-93 | 9 |Course Over Ground |course |0 to 359 degrees, +| | | | |511 = not available +|94-94 | 1 |GNSS Position status|gnss |0 = current GNSS position +| | | | |1 = not GNSS position (default) +|95-95 | 1 |Spare | |Not used +|============================================================================== + +Note: Type 27 has not been observed in the wild as of early 2011. + == Local extensions == Some regional authorities extend the AIS message set. @@ -3177,7 +3216,7 @@ controlled-vocabulary fields. An AIS-JSON object may have the optional attribute "scaled":true to signify that the rest of its fields are scaled; if this attribute has the value 'false' or is omitted, no scaling has been performed. Message types for which the unscaled and -scaled dumps will differ are 1-5, 9, 11, 17-19, and 21-24. +scaled dumps will differ are 1-5, 9, 11, 17-19, 21-24, and 27. 5. In unscaled mode, float-valued fields are dumped in their unscaled integer form. In scaled mode, division or other specified scaling is @@ -3212,6 +3251,7 @@ integer indices. In scaled mode, the values are dumped as strings. | 21 | lon, lat | aid_type, epfd | 22-23 | ne_lon,ne_lat, sw_lon, sw_lat | - | 24 | - | shiptype +| 27 | lon, lat | - |=========================================================================== As the Beaufort scale is usually quoted numerically, conforming implementations @@ -3387,8 +3427,8 @@ Version 1.27 describes the sometime U.S. practice of omitting the leading Version 1.28 merges updates from IMO 289, communicated by Kurt Schwehr. -Version 1.29 added much information on WMO special message format in +Version 1.29 added much information on WMO special message formats in types 6 and 8. Version 1.30 was revised because M.1371-4 is now a free download. -Also, we describe "pilot plugs". +Also, we describe "pilot plugs" and AIS message type 27. |