AIS Message Definitions

AIS Message: positionb (::)


Standard Class B equipment position report

See Also:

Name NumberOfBits ArrayLength Type Units Description
MessageID 6 uint AIS message number. Must be 18
RepeatIndicator 2 uint Indicated how many times a message has been repeated
0: default
3: do not repeat any more
UserID 30 uint Unique ship identification number (MMSI)
Reserved1 8 uint Reseverd for definition by a compentent regional or local authority. Should be set to zero.
SOG 10 udecimal knots Speed over ground
102.2: 102.2 knots or higher
PositionAccuracy 1 uint Accuracy of positioning fixes
0: low (greater than 10 m)
1: high (less than 10 m)
longitude 28 decimal degrees Location of the vessel East West location
latitude 27 decimal degrees Location of the vessel North South location
COG 12 udecimal degrees Course over ground
TrueHeading 9 uint degrees True heading (relative to true North)
TimeStamp 6 uint seconds UTC second when the report was generated
60: not available/default
61: manual input
62: dead reckoning
63: inoperative
Spare 2 uint Not used. Should be set to zero.
cs_unit 1 bool Does this unit do Carrier Sense?
False: Class B SOTDMA unit
True: Class B CS unit
display_flag 1 bool Does this class B unit have an integrated display?
False: No display
True: Integrated Display
dsc_flag 1 bool Does it have dedicated or time-shared DSC radio function?
False: No DSC function
True: Has DSC
band_flag 1 bool How flexible is the freq handling of the unit?
False: Upper 525 kHz band
True: Whole marine band
msg22_flag 1 bool Can the unit handle msg 22?
False: No freq management
True: Freq management with msg 22
mode_flag 1 bool Assigned mode wrt to VDL slots
False: Autonomous and continuous mode
True: Assigned mode
RAIM 1 bool Receiver autonomous integrity monitoring flag
False: not in use
True: in use
CommStateSelector 1 uint SOTDMA or ITDMA
CommState 19 uint Not decoded by this software yet