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Short Description
The ais-filedump utility allows flat file archival of AIS messages from TCP sources
Full Description



DMA AisLib is a Java library for handling AIS messages. This include

  • Reading from AIS sources e.g. serial connection, TCP connection or file
  • Handling of proprietary source tagging sentences
  • Message filtering like doublet filtering and down sampling
  • Decoding sentences and AIS messages
  • Encoding sentences and AIS messages
  • Sending AIS messages #6, #8, #12 and #14
  • Handling application specific messages

The library contains test code and utility applications demonstrating
the use.


  • Java 8
  • Maven 3


To build

mvn clean install

To run tests

mvn test

Developing in Eclipse

Use M2 plugin or

mvn eclipse:eclipse

and import as regular project.


You're encouraged to contribute to AisLib. Fork the code from and submit pull requests.


This library is licensed under the Apache License, Version 2.0.


Simple read and message handling

Reading from files or TCP/UDP connections is very simple with AisLib. In the example below messages
are read from a file.

AisReader reader = AisReaders.createReaderFromInputStream(new FileInputStream("sentences.txt"));
reader.registerHandler(new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        System.out.println("message id: " + aisMessage.getMsgId());

Reading using a TCP connection:

AisReader reader = AisReaders.createReader("localhost", 4001);
reader.registerHandler(new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        System.out.println("message id: " + aisMessage.getMsgId());

If the connection is broken the reader will try to reconnect after a certain amount of
time that can be set with:


A read timeout can be defined for the reader. If no data is received within this period
the connection will be closed and a reconnect will be tried.

Reading using an UDP connection:

AisReader reader = AisReaders.createUdpReader(8888);
reader.registerHandler(new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        System.out.println("message id: " + aisMessage.getMsgId());

Reading raw message packets

Instead of working with AisMessage objects, it is possible to work
with unparsed raw message packets (proprietary tags, comment blocks and VDM's).
A packet consumer is registred in a reader.

AisReader reader = AisReaders.createReader("localhost", 4001);
reader.registerPacketHandler(new Consumer<AisPacket>() {
    public void accept(AisPacket packet) {
        try {
            AisMessage message = packet.getAisMessage();
        } catch (AisMessageException | SixbitException e) {
            // Handle
        // Alternative returning null if no valid AIS message
        AisMessage message = packet.tryGetAisMessage();

        Date timestamp = packet.getTimestamp();
        CommentBlock cb = packet.getVdm().getCommentBlock();

Alternatively packets can be read as a packet stream.

Path path = ...
try (AisPacketReader pReader = AisPacketReader.createFromFile(path, true)) {
    AisPacket p;
    while ((p = pReader.readPacket()) != null) {
        // Handle packet

If the filename has '.zip' suffix decompression will automatically be applied.

Reader factory methods

An AisReader instance is created using factory methods in AisReaders. The following
methods can be used.

  • createReader(String hostname, int port) - Creates a reader connection to host:port.
  • createReader(String commaHostPort) - Creates a {@link AisTcpReader} from a list of one or more hosts on the
    form: host1:port1,...,hostN:portN. If more than one host/port round robin will be used.
  • createUdpReader(int port) - Creates a UDP reader reading from port on any interface.
  • createUdpReader(String address, int port) - Creates a UDP reader reading from port on interface with address.
  • createReaderFromInputStream(InputStream inputStream) - Creates a reader reading from an input stream.
  • createReaderFromFile(String filename) - Creates a reader reading from a file. If the filename suffix is '.zip' or '.gz',
    zip or gzip decompression will be applied respectively.

Reader group

A collection of readers can be organized in an AisReaderGroup that will deliver packets in a
single join packet stream. Sources are defined by a commaseparated list of host:port. If more than
one host for each source, round robin reading is used.

List<String> sources = ...
AisReaderGroup g = AisReaders.createGroup("name", sources);


Working with messages

To determine what messages are received the instanceof operator can be used. The example
below shows how to test and cast, and take advantage of the object oriented design where
related messages shares parents.

public void accept(AisMessage aisMessage) {
    // Handle AtoN message
    if (aisMessage instanceof AisMessage21) {
        AisMessage21 msg21 = (AisMessage21) aisMessage;
        System.out.println("AtoN name: " + msg21.getName());
    // Handle position messages 1,2 and 3 (class A) by using their shared parent
    if (aisMessage instanceof AisPositionMessage) {
        AisPositionMessage posMessage = (AisPositionMessage)aisMessage;
        System.out.println("speed over ground: " + posMessage.getSog());
    // Handle position messages 1,2,3 and 18 (class A and B)
    if (aisMessage instanceof IGeneralPositionMessage) {
        IGeneralPositionMessage posMessage = (IGeneralPositionMessage)aisMessage;
        System.out.println("course over ground: " + posMessage.getCog());
    // Handle static reports for both class A and B vessels (msg 5 + 24)
    if (aisMessage instanceof AisStaticCommon) {
        AisStaticCommon staticMessage = (AisStaticCommon)aisMessage;
        System.out.println("vessel name: " + staticMessage.getName());

See UML diagram of messages

Multiple sources

The example below shows how messages from multiple sources can be handled by a single

// Make a handler
Consumer<AisMessage> handler = new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        System.out.println("aisMessage: " + aisMessage);

// Make readers and register handler
AisReader reader1 = AisReaders.createReader("host1", 4001);
AisReader reader2 = AisReaders.createReader("host2", 4001);
AisReader reader3 = AisReaders.createReader("host3", 4001);

// Start readers
reader1.start(); reader2.start(); reader3.start();

Alternatively an AisReaderGroup can be used.

Round robin reading

The example below shows how to round robin between TCP hosts. If
one goes down, the re-connect will be to the next on the list.

AisReader reader = AisReaders.createReader("host1:port1,host2:port2,host3:port3");
reader.registerHandler(new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        System.out.println("message id: " + aisMessage.getMsgId());

Message filtering

Message filters implement a single method

 boolean rejectedByFilter(AisMessage message);

Down sample example:

AisReader reader = AisReaders.createReader("");
reader.registerHandler(new Consumer<AisMessage>() {
    DownSampleFilter downSampleFilter = new DownSampleFilter(60);
    public void accept(AisMessage aisMessage) {
        if (downSampleFilter.rejectedFilter(aisMessage)) {
        // Handle message

A MessageHandlerFilter can be used to put in between readers
and handlers. In the example below two filters are used. A doublet
filter and a down sampling filter.

Consumer<AisMessage> handler = new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        // Handle doublet filtered down sampled messages

// Make down sampling filter with sampling rate 1 min and
// make handler the recipient of down sampled messages
MessageHandlerFilter downsampleFilter = new MessageHandlerFilter(new DownSampleFilter());

// Make doublet filter with default window of 10 secs.
// Set down sample filter as recipient of doublet filered messages
MessageHandlerFilter doubletFilter = new MessageHandlerFilter(new DuplicateFilter());

// Make reader
AisReader reader = AisReaders.createReader(host, port);

Expression based packet filtering

It is also possible to perform packet filtering based on packet sources and contents using free-text expressions.
These expressions must comply with a specified grammar.

Using the filter

The expression filter can be used programmatically like this:

Filtering on packets source
import static dk.dma.ais.packet.AisPacketFiltersExpressionFilterParser.parseExpressionFilter;
parseExpressionFilter(" = DNK & s.type = LIVE").test(aisPacket);

In this example the test method wll return true for all packets received from a source in Denmark ('DNK') and
coming from a terrestrial source (typically a VHF base station as opposed to e.g. data received via satellite).
For packets coming sources not fulfilling this expression the test method will return false.

Filtering on source attributes is indicated by the 's' in front of the field ('country').

Filtering on message contents
import static dk.dma.ais.packet.AisPacketFiltersExpressionFilterParser.parseExpressionFilter;
parseExpressionFilter("m.pos witin circle(37.9121, -122.4229, 2000)").test(aisPacket);

In this example the test method will return false for packets containing a position outside a cartesian circle
centered in 37.912 degrees north (37°N54'44"), 122.4229 degrees west (22°W25'22"), and with a radius of 2000 meters.
For other packets (including packets without any position information) the method will return true.

Filtering on message (~packet) attributes is indicated by the 'm.' in front of the field ('pos').

Filtering on targets

In some cases it is insufficient to filter on packet sources and content alone. For instance it may be desirable to
block AIS packets with static and voyage related data (see class AisStaticCommon) for vessels which are outside a
given area. Since the AisStaticCommon messages do not contain any position information, it is not possible to filter
on these packets alone.

Instead, it is possible to use an expression filter which will "remember" all AIS packets it has previously been
served. It uses these messages to track all AIS targets and keep a cache of the latest known positions, speeds, and
other characteristis. This why, it is possible to filter on the target's characteristics rather than the latest packet

As an example:

import static dk.dma.ais.packet.AisPacketFiltersExpressionFilterParser.parseExpressionFilter;
parseExpresionFiter("t.sog > 10").test(aisPacket);

Of all packets send to the test-method only those which are related to a vesel with a speed over ground larger
than 10 knots will result in true being returned from test. This is true even for e.g. AIS messages of type 5
which contain no speed information.

Filtering on target attributes is indicated by the 't.' in front of the field ('sog').

Example application

An example of an existing application which uses the expression filter is AisFilter which is based on main class

java dk.dma.ais.utils.filter.Aisilter -t localhost:4001 -exp ".sog in 2..8"

This will make the application connect via TCP to localhost:4001 to receive AIS packets, filter them using the
supplied expression (so that packets with speed over ground outside the range 2 to 8 knots are rejected), and
output the remaining packets on the standard output.


The full grammar is specified usit ANTLR notation in file expresionFilter.g4.

The following are examples of filter expressions:

Simple comparisons
  • m.sog = 0
  • m.sog != 0
  • m.sog > 6.0
  • m.sog < 7.0
  • m.sog >= 6.6
  • m.sog <= 6.6
In lists
  • m.month = jan,feb,mar
  • m.month = (jan,feb,mar)
  • m.month in jan,feb,mar
  • m.month in (jan,feb,mar)
  • m.month @ jan,feb,mar
  • m.month @ (jan,feb,mar)
  • m.mmsi in 220431000,220435325,220430999
  • m.mmsi in (220431000,220435325,220430999)

  • m.month != jan,feb,mar

  • m.month != (jan,feb,mar)
  • m.month not in jan,feb,mar
  • m.month not in (jan,feb,mar)
  • m.month !@ jan,feb,mar
  • m.month !@ (jan,feb,mar)
  • m.mmsi not in 220431000,220435325,220430999
  • m.mmsi not in (220431000,220435325,220430999)
In ranges
  • = 5..15
  • in 5..15
  • in (5..15)
  • @ (5..15)

  • != 5..15

  • not in 5..15
  • !@ (5..15)
Within geographical areas
  • m.pos within circle(37.9058, -122.4310, 1000)
  • m.pos within bbox(37.9058, -122.4310, 37.9185, -122.4149)
With string resembling glob
  • like D*
  • LIKE DI*
  • ~ D*A
  • ~ 'DIA*'
Named values
  • m.type = TANKER
  • m.type = military
  • m.type in 'tanker', 'military', HSC
Composite expressions with boolean and/or
  • = 1 & m.sog >= 6.1 & m.sog <= 6.9
  • m.sog > 6.6 | m.sog < 6.4
  • m.sog > 6.6 & m.sog < 6.7
  • s.type=SAT||

The following fields can be used in filter expressions

Group Field Meaning Example values
sources Source id Source base station Source country DNK
s.type Source type LIVE, SAT
s.region Source region 0
<hr> <hr> <hr> <hr>
messages Message type 1, 2, 3, 5
m.mmsi MMSI number 219010123
m.year Msg recv'd in year 2014
m.month Msg recv'd in month jan, january, 1
m.dom Msg recv'd on day-of-month 1, 31
m.dow Msg recv'd on day-of-week mon, monday, 1
m.hour Msg recv'd on hour 14
m.minute Msg recv'd on minute 34
<hr> <hr> <hr> <hr>
m.imo IMO number 6159463
m.type Ship type tanker, 32
m.navstat Navigational status AT_ANCHOR, 1 Ship name Maersk Alabama
m.cs Radio call sign XP1234
m.sog Speed over ground 10.0
m.cog Course over ground 234
m.hdg True heading 180
m.draught Current draught 4.6 Latitude 56.1234
m.lon Longitude 12.4321
m.pos(*) Position (56.1234, 12.4321)
<hr> <hr> <hr> <hr>
targets t.imo IMO number 6159463
t.type Ship type tanker, 32
t.navstat Navigational status AT_ANCHOR, 1 Ship name Maersk Alabama
t.cs Radio call sign XP1234
t.sog Speed over ground 10.0
t.cog Course over ground 234
t.hdg True heading 180
t.draught Current draught 4.6 Latitude 56.1234
t.lon Longitude 12.4321
t.pos(*) Position (56.1234, 12.4321)

(*) pos is represents same values as (lat, lon) but is used in contexts where complete position (not just latitude or
longitude) is used.

Packet transformers

TBD. See dk.dma.ais.transform.*, dk.dma.ais.transform.TransformTest and

Reading proprietary tags

AisLib can handle some proprietary tags inserted before VDM sentences, but
implementations of factories must be given. In the example below Gatehouse
source tags are handled.

Proprietary factories are defined in the file

AisReader reader = AisReaders.createReaderFromInputStream(new FileInputStream("sentences.txt"));
reader.registerHandler(new Consumer<AisMessage>() {
    public void accept(AisMessage aisMessage) {
        if (aisMessage.getSourceTag() != null) {
            IProprietarySourceTag sourceTag = aisMessage.getSourceTag();
            System.out.println("timestamp: " + sourceTag.getTimestamp());

AIS metadata

Besides from propritary tags, comment blocks carry metadata about
the VDM sentences carrying the AIS message.

The example below shows how to handle comment blocks.

AisReader reader = ...
reader.registerPacketHandler(new Consumer<AisPacket>() {
    public void accept(AisPacket aisPacket) {
        Vdm vdm = packet.getVdm();
        if (vdm == null) {
        CommentBlock cb = vdm.getCommentBlock();
        if (cb != null) {
            String source = cb.getString();
            Long cbTimestamp = cb.getTimestamp();

Common metadata has been standardized in the class AisPacketTags. The
following attributes are used:

  • Timestamp
  • Source id
  • Source basestation
  • Source country (ISO three letter)
  • Source type SAT | LIVE


AisPacketTags tags = packet.getTags();
Assert.assertEquals(tags.getTimestamp().getTime(), 1354719387000L);
Assert.assertEquals(tags.getSourceId(), "SISSM");
Assert.assertEquals(tags.getSourceBs().intValue(), 2190047);
Assert.assertEquals(tags.getSourceCountry().getThreeLetter(), "DNK");

Full timestamp of VDM sentences are done in different proprietary fashions. AisLib
tries to get the timestamp in three ways

  1. Comment block key 'c'
  2. Gatehouse propritary source tag
  3. MSSIS timestamp appended to VDM sentence (the first occurence of a timestamp is used)

The timestamp is retrived from a packet using the following

Packet packet = ...
Date timestamp = packet.getTimestamp();


TBD. See dk.dma.ais.bus.AisBusTest.

Sending a message

Example of sending an addressed text message in an ABM sentence. See test cases on how
to send application specific message. See AisReader for different sending options. In the
example below all ABM packaging is handled by AisReader.

AisReader aisReader = new AisTcpReader(host, port);
// Make AIS message 12
AisMessage12 msg12 = new AisMessage12();

// Send using a blocking call
Abk abk = aisReader.send(msg12, 1, destination);
if (abk.isSuccess()) {
} else {
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