AISutils is a valuable package of utility software to process AIS messages.
Currently it consist of a Tracker which can maintain the state of individual vessels between AIS messages received over time. Soon there will also be free-text filter expressions for AIS messages, event triggering, message archiving in Big Data stores, export of KML-files for Google Earth, and more.
Different types of AIS messages carry different types of information about the same physical vessel. For instance a vessel's name is carried in messages of type 5, whereas its position can be carried in messages of type 1.
In order to collect the complete information about a vessel, information split across different AIS messages must therefore be collected and consolidated. This is what the tracker does. Feed it with a AIS messages in NMEA format - and you will get Tracks in return.
So, consider that you have a finite or continuous stream of AIS data in NMEA format. Something like this:
...
!AIVDM,1,1,,A,15Mv5v?P00IS0J`A86KTROvN0<5k,0*12
!AIVDM,1,1,,A,15Mwd<PP00ISfGpA7jBr??vP0<3:,0*04
!AIVDM,2,1,4,B,55MwW7P00001L@?;GS0<51B08Thj0TdpE800000P0hD556IE07RlSm6P0000,0*0B
!AIVDM,2,2,4,B,00000000000,2*23
!AIVDM,1,1,,A,15N7th0P00ISsi4A5I?:fgvP2<40,0*06
!AIVDM,1,1,,A,15NIEcP000ISrjPA8tEIBq<P089=,0*63
!AIVDM,1,1,,B,15MuS0PP00IS00HA8gEtSgvN0<3U,0*61
!AIVDM,1,1,,A,16K8Au@000awU:FD9l?JcnrP289D,0*15
!AIVDM,1,1,,A,15MwP=0000ISS5lA7=qJ57jL05Ip,0*0D
...
Then you feed it into the tracker from a regular Java InputStream:
public class DemoApp {
public static void main(String [] args) throws IOException {
InputStream inputStream = ...
// Start tracking
AisTracker tracker = new AisTracker();
tracker.update(inputStream);
...
}
}As the tracker is reading the stream, it builds and maintains the state of each track. Information about the tracker and each track can be read out at any time from any thread:
public class DemoApp {
public printSomething {
// Get stats from tracker
System.out.println("No. of current tracks in tracker: " + tracker.getNumberOfAisTracks());
// Get all tracks from tracker
Set<AisTrack> tracks = tracker.getAisTracks();
AisTrack aRandomTrack = tracks.iterator().next();
System.out.println("A random MMSI " + aRandomTrack.getMmsi());
// Get a specific track from tracker
AisTrack track = tracker.getAisTrack(219997000);
System.out.println(
"Tracking vessel with name: " + track.getShipName() +
", callsign: " + track.getCallsign() +
" currently cruising at " + track.getSpeedOverGround() + " knots."
);
}
}In addition to this, it is possible register event listeners, so that your application is instantly notified whenever a track is created, updated, or deleted. The mechanism works like this:
import com.google.common.eventbus.Subscribe;
import dk.tbsalling.ais.tracker.AisTrack;
import dk.tbsalling.ais.tracker.AisTracker;
import dk.tbsalling.ais.tracker.events.AisTrackCreatedEvent;
import dk.tbsalling.ais.tracker.events.AisTrackDeletedEvent;
import dk.tbsalling.ais.tracker.events.AisTrackDynamicsUpdatedEvent;
import dk.tbsalling.ais.tracker.events.AisTrackUpdatedEvent;
...
public class EventDemoApp {
public static void main(String [] args) throws IOException, InterruptedException {
// Create the tracker
AisTracker tracker = new AisTracker();
// Register event listeners
tracker.registerSubscriber(new Object() {
@Subscribe
public void handleEvent(AisTrackCreatedEvent event) {
System.out.println("CREATED: " + event.getAisTrack());
}
@Subscribe
public void handleEvent(AisTrackUpdatedEvent event) {
System.out.println("UPDATED: " + event.getAisTrack());
}
@Subscribe
public void handleEvent(AisTrackDynamicsUpdatedEvent event) {
System.out.println("UPDATED DYNAMICS: " + event.getAisTrack());
}
@Subscribe
public void handleEvent(AisTrackDeletedEvent event) {
System.out.println("DELETED: " + event.getAisTrack());
}
});
// Feed AIS Data into tracker
InputStream aisInputStream = ...;
tracker.update(aisInputStream);
}
}As the input stream is read, this will produce output like this:
CREATED: AisTrack{mmsi=258315000, transponderClass=A, callsign='LFNA', shipName='FALKVIK', shipType=CargoNoAdditionalInfo, toBow=40, toStern=10, toStarboard=5, toPort=4, latitude=null, longitude=null, speedOverGround=null, courseOverGround=null, trueHeading=null, second=null}
CREATED: AisTrack{mmsi=440009390, transponderClass=A, callsign='null', shipName='null', shipType=null, toBow=null, toStern=null, toStarboard=null, toPort=null, latitude=37.452908, longitude=126.611946, speedOverGround=0.0, courseOverGround=55.2, trueHeading=511, second=15}
UPDATED: AisTrack{mmsi=366970360, transponderClass=A, callsign='null', shipName='null', shipType=null, toBow=null, toStern=null, toStarboard=null, toPort=null, latitude=29.93085, longitude=-90.2198, speedOverGround=0.0, courseOverGround=116.1, trueHeading=511, second=15}
UPDATED DYNAMICS: AisTrack{mmsi=366970360, transponderClass=A, callsign='null', shipName='null', shipType=null, toBow=null, toStern=null, toStarboard=null, toPort=null, latitude=29.93085, longitude=-90.2198, speedOverGround=0.0, courseOverGround=116.1, trueHeading=511, second=15}
CREATED: AisTrack{mmsi=244670316, transponderClass=A, callsign='null', shipName='null', shipType=null, toBow=null, toStern=null, toStarboard=null, toPort=null, latitude=51.89475, longitude=4.379285, speedOverGround=0.0, courseOverGround=70.6, trueHeading=511, second=14}
CREATED: AisTrack{mmsi=205264890, transponderClass=A, callsign='null', shipName='null', shipType=null, toBow=null, toStern=null, toStarboard=null, toPort=null, latitude=51.309635, longitude=4.3227935, speedOverGround=0.0, courseOverGround=338.0, trueHeading=339, second=15}
...
The AIS filter package offers a number of different filters, which can be used to filter AIS messages in a stream of messages. All filters are implemented as Java Predicates, like this:
Predicate<AISMessage> filter = ...;
Filters can be used as-is/standalone by applying them to AISMessages, or they can supplied to e.g. the AISTracker to filter the AISMessages used to update tracks by e.g. geography, ship type or to avoid duplicate messages. An AISTracker using a filter, can be instantiated like this:
Predicate<AISMessage> filter = ...;
AisTracker tracker = new AisTracker(filter);
Filters can be chained by applying the 'and', 'or' and 'negate' features of the Java Predicate<> interface.
The expression filter class allows the programmer (or end user) to express a filter expression in free text, and apply this against AISMessages.
The filter is instantiated from the FilterFactory like this:
Predicate<AISMessage> expressionFilter = FilterFactory.newExpressionFilter("msgid=3");
This expressionFilter will return true only for AISMessages of type 3.
The expression grammar supports a number of free text expressions. Other possible expressions are:
FilterFactory.newExpressionFilter("msgid=3 or msgid=5");
FilterFactory.newExpressionFilter("msgid in (1, 2, 3, 5)");
FilterFactory.newExpressionFilter("msgid not in (1, 2, 3, 5");
FilterFactory.newExpressionFilter("mmsi > 100000000 and mmsi < 219000000 and msgid in (1, 2, 3, 5)");
FilterFactory.newExpressionFilter("sog > 5.0");
FilterFactory.newExpressionFilter("cog < 180.0");
FilterFactory.newExpressionFilter("lat > 55.0 and lat < 55.5 and lng > 10.0 and lng < 10.5");
etc.
In some systems it is normal to observe duplicate AIS messages in the message stream. This happens for instance in systems where several AIS receivers have overlapping geographical receival areas. In this case a transmission from a vessel can be picked up by more than one receiver and thus cause doublets in the message stream.
The doublet filter works by appying a sliding time window over the message stream. If a message occurs more than one time inside a time window of, say, 15 seconds, then only the first message will pass through the filter.
Duplicate filters are also instantiated through the FilterFactory class, like this:
Predicate<AISMessage> doubletFilter = FilterFactory.newDoubletFilter(15, TimeUnit.SECONDS);
You do not need to compile AISutils yourself. It is available in Maven Central. So if you are using Maven, all you need to do is add these lines to your pom.xml:
<dependency>
<groupId>dk.tbsalling</groupId>
<artifactId>aisutils</artifactId>
<version>1.0.0</version>
</dependency>If you need a bleeding edge version, which is not yet released, then you can download AISutils from Github and and build yourself it using maven:
$ git clone git@github.com:tbsalling/aisutils.git
...
$ cd aisutils/
$ mvn install
Then add this to the pom.xml file of your own Java Maven project:
<dependency>
<groupId>dk.tbsalling</groupId>
<artifactId>aisutils</artifactId>
<version>1.0.1-SNAPSHOT</version>
</dependency>
More advanced free-text filter expressions for AIS messages event triggering message archiving in Big Data stores export of KML-files for Google Earth