/Users/brianlane/projs/aisparser/c/src/vdm_parse.c File Reference

Detailed Description

AIVDM/AIVDO AIS Sentence Parser.

Author:
Copyright 2006-2008 by Brian C. Lane <bcl@brianlane.com>, All Rights Reserved
Version:
1.8
This module contains the functions to parse incoming Automatic Identification System (AIS) serial messages as defined by IEC-61993-2 Each message type has its own structure, of the form aismsg_XX, based on the message id of the message. The parse routine for each message is of the form parse_ais_<msgid>, eg, parse_ais_5()

Each of the aismsg_XX parsing functions expect to be passed a pointer to a ais_sate structure containing the raw 6-bit data and a pointer to the aismsg_XX structure to place the parsed information into.

All aismsg_XX structures are cleared by their respecive parsers, except for parse_ais_24() which stores 2 messages into a single structure.

Data like the ship's name and callsign are converted to ASCII before being stored. Positions are converted to signed long values, and other fields like course over ground, speed, heading, etc. are left for further decoding. 1/1000 minute positions are converted to 1/10000 minute positions to make comparisons easier.

Not all of these parsers have been fully tested with live data. Here is a list of the ones that have been tested so far: 1,3,4,5,7,12,15,20

If you have valid data for other message ids and would like to contribute them please email them to bcl@brianlane.com

Example: 

    ais_state ais;
    aismsg_1  msg_1;
    char buf[256];

    memset( &state, 0, sizeof(state) );

    // Process incoming packets from some source
    while( message_source_active )
    {
        // Get your messages from your source, whatever that may be
        fill_buf( buf, 255);

        // Is there a complete message available?
        if (assemble_vdm( &ais, buf ) == 0)
        {
            // Get the 6 bit message id
            ais.msgid = (unsigned char) get_6bit( &ais.six_state, 6 );
            
            // process message with appropriate parser
            switch( ais.msgid ) {
                case 1:
                    if( parse_ais_1( &ais, &msg_1 ) == 0 )
                    {
                        // Successfully parsed a message 1 into msg_1 struct
                    }
                    break;
            }
        }
    }

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "portable.h"
#include "nmea.h"
#include "sixbit.h"
#include "vdm_parse.h"

Functions

int __stdcall get_timetag (sixbit *state, timetag *datetime)
 Get 20 bit ETA, Seaway and IMO Timetag.
void __stdcall conv_sign (unsigned int sign_bit, int *value)
 Convert a 2's complement value to a signed integer value.
char __stdcall ais2ascii (char value)
 Convert a AIS 6-bit character to ASCII.
int __stdcall pos2ddd (long latitude, long longitude, double *lat_dd, double *long_ddd)
 Convert 1/10000 minute position to signed DD.DDDDDD format.
int __stdcall pos2dmm (long latitude, long longitude, short *lat_dd, double *lat_min, short *long_ddd, double *long_min)
 Convert 1/10000 minute position to signed DD MM.MMMM format.
int __stdcall conv_pos (long *latitude, long *longitude)
 Convert unsigned 1/10000 minute position to signed.
int __stdcall assemble_vdm (ais_state *state, char *str)
 Assemble AIVDM/VDO sentences.
int __stdcall parse_ais_1 (ais_state *state, aismsg_1 *result)
 Parse an AIS message 1 into an aismsg_1 structure.
int __stdcall parse_ais_2 (ais_state *state, aismsg_2 *result)
 Parse an AIS message 2 into an aismsg_2 structure.
int __stdcall parse_ais_3 (ais_state *state, aismsg_3 *result)
 Parse an AIS message 3 into an aismsg_3 structure.
int __stdcall parse_ais_4 (ais_state *state, aismsg_4 *result)
 Parse an AIS message 4 into an aismsg_4 structure.
int __stdcall parse_ais_5 (ais_state *state, aismsg_5 *result)
 Parse an AIS message 5 into an aismsg_5 structure.
int __stdcall parse_ais_6 (ais_state *state, aismsg_6 *result)
 Parse an AIS message 6 into an aismsg_6 structure.
int __stdcall parse_ais_7 (ais_state *state, aismsg_7 *result)
 Parse an AIS message 7 into an aismsg_7 structure.
int __stdcall parse_ais_8 (ais_state *state, aismsg_8 *result)
 Parse an AIS message 8 into an aismsg_8 structure.
int __stdcall parse_ais_9 (ais_state *state, aismsg_9 *result)
 Parse an AIS message 9 into an aismsg_9 structure.
int __stdcall parse_ais_10 (ais_state *state, aismsg_10 *result)
 Parse an AIS message 10 into an aismsg_10 structure.
int __stdcall parse_ais_11 (ais_state *state, aismsg_11 *result)
 Parse an AIS message 11 into an aismsg_11 structure.
int __stdcall parse_ais_12 (ais_state *state, aismsg_12 *result)
 Parse an AIS message 12 into an aismsg_12 structure.
int __stdcall parse_ais_13 (ais_state *state, aismsg_13 *result)
 Parse an AIS message 13 into an aismsg_13 structure.
int __stdcall parse_ais_14 (ais_state *state, aismsg_14 *result)
 Parse an AIS message 14 into an aismsg_14 structure.
int __stdcall parse_ais_15 (ais_state *state, aismsg_15 *result)
 Parse an AIS message 15 into an aismsg_15 structure.
int __stdcall parse_ais_16 (ais_state *state, aismsg_16 *result)
 Parse an AIS message 16 into an aismsg_16 structure.
int __stdcall parse_ais_17 (ais_state *state, aismsg_17 *result)
 Parse an AIS message 17 into an aismsg_17 structure.
int __stdcall parse_ais_18 (ais_state *state, aismsg_18 *result)
 Parse an AIS message 18 into an aismsg_18 structure.
int __stdcall parse_ais_19 (ais_state *state, aismsg_19 *result)
 Parse an AIS message 19 into an aismsg_19 structure.
int __stdcall parse_ais_20 (ais_state *state, aismsg_20 *result)
 Parse an AIS message 20 into an aismsg_20 structure.
int __stdcall parse_ais_21 (ais_state *state, aismsg_21 *result)
 Parse an AIS message 21 into an aismsg_21 structure.
int __stdcall parse_ais_22 (ais_state *state, aismsg_22 *result)
 Parse an AIS message 22 into an aismsg_22 structure.
int __stdcall parse_ais_23 (ais_state *state, aismsg_23 *result)
 Parse an AIS message 23 into an aismsg_23 structure.
int __stdcall parse_ais_24 (ais_state *state, aismsg_24 *result)
 Parse an AIS message 24 into an aismsg_24 structure.

Function Documentation

char __stdcall ais2ascii ( char  value  ) 

Convert a AIS 6-bit character to ASCII.

Parameters:
value 6-bit value to be converted
return

This function is used to convert binary data to ASCII. This is different from the 6-bit ASCII to binary conversion for VDM messages; it is used for strings within the datastream itself. eg. Ship Name and Destination.

int __stdcall assemble_vdm ( ais_state *  state,
char *  str 
)

Assemble AIVDM/VDO sentences.

This function handles re-assembly and extraction of the 6-bit data from AIVDM/AIVDO sentences.

Because the NMEA standard limits the length of a line to 80 characters some AIS messages, such as message 5, are output as a multipart VDM messages. This routine collects the 6-bit encoded data from these parts and returns a 1 when all pieces have been reassembled.

It expects the sentences to:

It will return an error if it receives a piece out of order or from a new sequence before the previous one is finished.

Returns

Example: 

    ais_state state;
    char buf[3][255] = { "!AIVDM,1,1,,B,19NS7Sp02wo?HETKA2K6mUM20<L=,0*27\r\n",
                         "!AIVDM,2,1,9,A,55Mf@6P00001MUS;7GQL4hh61L4hh6222222220t41H,0*49\r\n",
                         "!AIVDM,2,2,9,A,==40HtI4i@E531H1QDTVH51DSCS0,2*16\r\n"
                       };
    
    memset( &state, 0, sizeof(state) );
    assemble_vdm( &state, buf[0] )
    state.six_state now has the 6-bit data from the message

    assemble_vdm( &state, buf[1] );
    This returns a 1 because not all the pieces have been received.
    
    assemble_vdm( &state, buf[2] );
    This returns a 0 and state.six_state has the complete 6-bit data for
    the message 5.

int __stdcall conv_pos ( long *  latitude,
long *  longitude 
)

Convert unsigned 1/10000 minute position to signed.

Parameters:
latitude pointer to an unsigned latitude
longitude pointer to an unsigned longitude
This function converts the raw 2's complement values to signed long 1/10000 minute position. It is used internally by all of the messages that contain position information.

void __stdcall conv_sign ( unsigned int  sign_bit,
int *  value 
)

Convert a 2's complement value to a signed integer value.

Parameters:
sign_bit 
value pointer to value
eg. to convert a 10 bit 2's complement: conv_sign( 0x00200, &temp );

int __stdcall get_timetag ( sixbit *  state,
timetag *  datetime 
)

Get 20 bit ETA, Seaway and IMO Timetag.

Parameters:
state pointer to parser state
datetime pointer to timetag result struct
return

int __stdcall parse_ais_1 ( ais_state *  state,
aismsg_1 *  result 
)

Parse an AIS message 1 into an aismsg_1 structure.

Ship Position report with SOTDMA Communication state

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall parse_ais_10 ( ais_state *  state,
aismsg_10 *  result 
)

Parse an AIS message 10 into an aismsg_10 structure.

UTC and Date Inquiry

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

int __stdcall parse_ais_11 ( ais_state *  state,
aismsg_11 *  result 
)

Parse an AIS message 11 into an aismsg_11 structure.

UTC and Date Response

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

int __stdcall parse_ais_12 ( ais_state *  state,
aismsg_12 *  result 
)

Parse an AIS message 12 into an aismsg_12 structure.

Addressed Safety Related Message

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

The safety message is converted to ASCII before storage in the result->message field.

int __stdcall parse_ais_13 ( ais_state *  state,
aismsg_13 *  result 
)

Parse an AIS message 13 into an aismsg_13 structure.

Safety Related Acknowledge

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return

Depending on the length of the message some of the fields may be 0. result->num_acks has the number of acks received.

int __stdcall parse_ais_14 ( ais_state *  state,
aismsg_14 *  result 
)

Parse an AIS message 14 into an aismsg_14 structure.

Safety Related Broadcast

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

The safety message is converted to ASCII before storage in the result->message field.

int __stdcall parse_ais_15 ( ais_state *  state,
aismsg_15 *  result 
)

Parse an AIS message 15 into an aismsg_15 structure.

Interrogation

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return

Depending on the length of the message some if the fields may be 0. result->num_reqs has the number of interrogation requests.

int __stdcall parse_ais_16 ( ais_state *  state,
aismsg_16 *  result 
)

Parse an AIS message 16 into an aismsg_16 structure.

Assigned mode command

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return

Depending on the length of the message some of the fields may be 0. result->num_cmds has the number of commands received.

int __stdcall parse_ais_17 ( ais_state *  state,
aismsg_17 *  result 
)

Parse an AIS message 17 into an aismsg_17 structure.

GNSS Binary Broadcast Message

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note: the binary payload of the message is left in its 6-bit ASCII form when stored into result->data. This allows the data to be passed to the sixbit module for parsing.

int __stdcall parse_ais_18 ( ais_state *  state,
aismsg_18 *  result 
)

Parse an AIS message 18 into an aismsg_18 structure.

Class B Position Report

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall parse_ais_19 ( ais_state *  state,
aismsg_19 *  result 
)

Parse an AIS message 19 into an aismsg_19 structure.

Extended Class B Position Report

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned. And the ship's name is converted to ASCII before being stored.

int __stdcall parse_ais_2 ( ais_state *  state,
aismsg_2 *  result 
)

Parse an AIS message 2 into an aismsg_2 structure.

Ship Position report with SOTDMA Communication state

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall parse_ais_20 ( ais_state *  state,
aismsg_20 *  result 
)

Parse an AIS message 20 into an aismsg_20 structure.

Data link management message

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Depending on the length of the message some fields may be 0. result->num_cmds will have the number of commands received.

int __stdcall parse_ais_21 ( ais_state *  state,
aismsg_21 *  result 
)

Parse an AIS message 21 into an aismsg_21 structure.

Aids To Navigation position report (AtoN)

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned. And the AtoN name and extended name are converted to ASCII before storage.

int __stdcall parse_ais_22 ( ais_state *  state,
aismsg_22 *  result 
)

Parse an AIS message 22 into an aismsg_22 structure.

Channel Management

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return

Check the addressed flag to decide whether to use the positions in NE and SW or the addresses in addressed_1 and addressed_2

Note that the latitudes and longitudes are converted to signed values before being returned and that they are converted to 1/10000 minute format from 1/1000 minute as received.

int __stdcall parse_ais_23 ( ais_state *  state,
aismsg_23 *  result 
)

Parse an AIS message 23 into an aismsg_23 structure.

Group Assignment Command

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitudes and longitudes are converted to signed values before being returned and that they are converted to 1/10000 minute format from 1/1000 minute as received.

int __stdcall parse_ais_24 ( ais_state *  state,
aismsg_24 *  result 
)

Parse an AIS message 24 into an aismsg_24 structure.

Class B"CS" Static Data Report

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled.
return:

NOTE! The result structure needs to be cleared before use. Because message 24 is a 2 part message the parse function doesn't clear the structure before filling it. You should do this:

       memset( result, 0, sizeof( aismsg_24 ));

before passing a message 24A to the parse_ais_24() function.

Message 24 is a 2 part message. The first part only contains the MMSI and the ship name. The second message contains the ship dimensions, etc.

Check the result->part_number field to determine which message this is. The same structure is used for both messages and the result->flags field will have a 0x03 in it when both messages have been parsed.

The ship name, vendor id and callsign are all converted to ASCII before storage.

int __stdcall parse_ais_3 ( ais_state *  state,
aismsg_3 *  result 
)

Parse an AIS message 3 into an aismsg_3 structure.

Ship Position report with ITDMA Communication state

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall parse_ais_4 ( ais_state *  state,
aismsg_4 *  result 
)

Parse an AIS message 4 into an aismsg_4 structure.

Base Station Report

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall parse_ais_5 ( ais_state *  state,
aismsg_5 *  result 
)

Parse an AIS message 5 into an aismsg_5 structure.

Ship Static and Voyage Data

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the ship's callsign, name and destination are converted to ASCII before storage.

int __stdcall parse_ais_6 ( ais_state *  state,
aismsg_6 *  result 
)

Parse an AIS message 6 into an aismsg_6 structure.

Addressed Binary Message

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note: the binary payload of the message is left in its 6-bit ASCII form when stored into result->data. This allows the data to be passed to the sixbit module for parsing.

int __stdcall parse_ais_7 ( ais_state *  state,
aismsg_7 *  result 
)

Parse an AIS message 7 into an aismsg_7 structure.

Binary acknowledge

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Depending on the length of the message some of the fields may be 0. result->num_acks has the number of acks received.

int __stdcall parse_ais_8 ( ais_state *  state,
aismsg_8 *  result 
)

Parse an AIS message 8 into an aismsg_8 structure.

Binary Broadcast Message

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note: the binary payload of the message is left in its 6-bit ASCII form when stored into result->data. This allows the data to be passed to the sixbit module for parsing.

int __stdcall parse_ais_9 ( ais_state *  state,
aismsg_9 *  result 
)

Parse an AIS message 9 into an aismsg_9 structure.

Search And Rescue(SAR) position report

Parameters:
state pointer to ais_state
result pointer to parsed message result structure to be filled
return:

Note that the latitude and longitude are converted to signed values before being returned.

int __stdcall pos2ddd ( long  latitude,
long  longitude,
double *  lat_dd,
double *  long_ddd 
)

Convert 1/10000 minute position to signed DD.DDDDDD format.

Parameters:
latitude signed latitude in 1/10000 minute format
longitude signed longitude in 1/10000 minute format
lat_dd pointer to hold signed latitude in DD.DDDDDD format
long_ddd pointer to hold signed longitude in DD.DDDDDD format
This function converts 1/10000 minute formatted positions to standard Degrees and decimal degrees format.

int __stdcall pos2dmm ( long  latitude,
long  longitude,
short *  lat_dd,
double *  lat_min,
short *  long_ddd,
double *  long_min 
)

Convert 1/10000 minute position to signed DD MM.MMMM format.

Parameters:
latitude signed latitude in 1/10000 minute format
longitude signed longitude in 1/10000 minute format
lat_dd pointer to hold signed latitude in DD format
lat_min pointer to hold minutes in mm.mmmm format
long_ddd pointer to hold signed longitude in DDD format
long_min pointer to hold minutes in mm.mmmm format
This function converts 1/10000 minute formatted positions to standard Degrees and decimal minutes format.

Generated on Tue Aug 26 13:57:50 2008 for AIS Parser by  doxygen 1.5.2