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This package supports the parsing of AIS messages in Java. AIS, the Automatic Identification System, is a system aiming at improving maritime safety by exchanging messages between ships, other vehicles in particular aircraft involved in search-and-rescue (SAR), and (fixed) base stations. To be precise, this package support the ITU-R M.1371-4 AIS standard.
See our extensive javadoc and in particular the class AISParser for more information on how to use this package.
The parser was used in the Poseidon project, and is improved in the Metis project to better handle uncertain information. Both projects were led by the Embedded Systems Institute. In both projects Thales Nederlands was the carrying industrial partner, and multiple Dutch universities participated.
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/* ESI AIS Parser
*
* Copyright 2011/2012 by Pierre van de Laar & Pierre America (Embedded Systems Institute)
* Copyright 2008 by Brian C. Lane
* All Rights Reserved
*
*/
package nl.esi.metis.aisparser.impl;
import nl.esi.metis.aisparser.AISMessage;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.VDMMessage;
import nl.esi.metis.aisparser.annotations.AISHypothesisAnnotation;
import nl.esi.metis.aisparser.annotations.AISInconsistentLengthForTypeAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;
public class AISMessageFactory {
/**
* Is valid VDMMessage, such that an AIS Message can be extracted from it?
* @param message
* @return is valid VDMMessage?
*/
static public boolean IsValid (VDMMessage message)
{
return message.atEnd() && message.isComplete();
}
/**
* Returns AISMessage that adheres to the specifications based on MessageType and Length
* @param sb
* @param provenance
* @return
*/
static private AISMessageImpl getAISMessageWithinSpecification (Sixbit sb, VDMMessageProvenance provenance)
{
int messageid = AISMessageImpl.getMessageID(sb);
switch (messageid)
{
case 1:
if (AISMessage01Impl.validLength(sb.length()))
{
return new AISMessage01Impl(sb, provenance);
}
break;
case 2:
if (AISMessage02Impl.validLength(sb.length()))
{
return new AISMessage02Impl(sb, provenance);
}
break;
case 3:
if (AISMessage03Impl.validLength(sb.length()))
{
return new AISMessage03Impl(sb, provenance);
}
break;
case 4:
if (AISMessage04Impl.validLength(sb.length()))
{
return new AISMessage04Impl(sb, provenance);
}
break;
case 5:
if (AISMessage05Impl.validLength(sb.length()))
{
return new AISMessage05Impl(sb, provenance);
}
break;
case 6:
if (AISMessage06Impl.validLength(sb.length()))
{
return new AISMessage06Impl(sb, provenance);
}
break;
case 7:
if (AISMessage07Impl.validLength(sb.length()))
{
return new AISMessage07Impl(sb, provenance);
}
break;
case 8:
if (AISMessage08Impl.validLength(sb.length()))
{
return new AISMessage08Impl(sb, provenance);
}
break;
case 9:
if (AISMessage09Impl.validLength(sb.length()))
{
return new AISMessage09Impl(sb, provenance);
}
break;
case 10:
if (AISMessage10Impl.validLength(sb.length()))
{
return new AISMessage10Impl(sb, provenance);
}
break;
case 11:
if (AISMessage11Impl.validLength(sb.length()))
{
return new AISMessage11Impl(sb, provenance);
}
break;
case 12:
if (AISMessage12Impl.validLength(sb.length()))
{
return new AISMessage12Impl(sb, provenance);
}
break;
case 13:
if (AISMessage13Impl.validLength(sb.length()))
{
return new AISMessage13Impl(sb, provenance);
}
break;
case 14:
if (AISMessage14Impl.validLength(sb.length()))
{
return new AISMessage14Impl(sb, provenance);
}
break;
case 15:
if (AISMessage15Impl.validLength(sb.length()))
{
return new AISMessage15Impl(sb, provenance);
}
break;
case 16:
if (AISMessage16Impl.validLength(sb.length()))
{
return new AISMessage16Impl(sb, provenance);
}
break;
case 17:
if (AISMessage17Impl.validLength(sb.length()))
{
return new AISMessage17Impl(sb, provenance);
}
break;
case 18:
if (AISMessage18Impl.validLength(sb.length()))
{
return new AISMessage18Impl(sb, provenance);
}
break;
case 19:
if (AISMessage19Impl.validLength(sb.length()))
{
return new AISMessage19Impl(sb, provenance);
}
break;
case 20:
if (AISMessage20Impl.validLength(sb.length()))
{
return new AISMessage20Impl(sb, provenance);
}
break;
case 21:
if (AISMessage21Impl.validLength(sb.length()))
{
return new AISMessage21Impl(sb, provenance);
}
break;
case 22:
if (AISMessage22Impl.validLength(sb.length()))
{
return new AISMessage22Impl(sb, provenance);
}
break;
case 23:
if (AISMessage23Impl.validLength(sb.length()))
{
return new AISMessage23Impl(sb, provenance);
}
break;
case 24:
{
// Distinguish between the different part numbers:
if (AISMessage24PartAImpl.valid(sb))
{
return new AISMessage24PartAImpl(sb, provenance);
}
else if (AISMessage24PartBImpl.valid(sb))
{
return new AISMessage24PartBImpl(sb, provenance);
}
break;
}
case 25:
if (AISMessage25Impl.valid(sb))
{
return new AISMessage25Impl(sb, provenance);
}
break;
case 26:
if (AISMessage26Impl.valid(sb))
{
return new AISMessage26Impl(sb, provenance);
}
break;
case 27:
if (AISMessage27Impl.validLength(sb.length()))
{
return new AISMessage27Impl(sb, provenance);
}
break;
}
return null;
}
public static AISMessageImpl AssumeMessageIdIsCorrect(VDMMessage message, Sixbit sb, VDMMessageProvenance provenance, AISInconsistentLengthForTypeAnnotation annotation)
{
/* We assume messageId as specified by message is OK
* We change length of message to adhere to the type's length
*/
AISMessageImpl retval;
int assumedMessageId = AISMessageImpl.getMessageID(sb);
switch (assumedMessageId)
{
case 1:
{
int diff = AISMessage01Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage01Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage01Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 2:
{
int diff = AISMessage02Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage02Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage02Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 3:
{
int diff = AISMessage03Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage03Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage03Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 4:
{
int diff = AISMessage04Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage04Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage04Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 5:
{
int diff = AISMessage05Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage05Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage05Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 6:
{
int diff = AISMessage06Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage06Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage06Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 7:
{
int diff = AISMessage07Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage07Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage07Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 8:
{
int diff = AISMessage08Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage08Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage08Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 9:
{
int diff = AISMessage09Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage09Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage09Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 10:
{
int diff = AISMessage10Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage10Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage10Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 11:
{
int diff = AISMessage11Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage11Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage11Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
} case 12:
{
int diff = AISMessage12Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage12Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage12Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 13:
{
int diff = AISMessage13Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage13Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage13Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 14:
{
int diff = AISMessage14Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage14Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage14Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 15:
{
int diff = AISMessage15Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage15Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage15Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 16:
{
int diff = AISMessage16Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage16Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage16Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 17:
{
int diff = AISMessage17Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage17Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage17Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 18:
{
int diff = AISMessage18Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage18Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage18Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 19:
{
int diff = AISMessage19Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage19Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage19Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 20:
{
int diff = AISMessage20Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage20Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage20Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 21:
{
int diff = AISMessage21Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage21Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage21Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
} case 22:
{
int diff = AISMessage22Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage22Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage22Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 23:
{
int diff = AISMessage23Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage23Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage23Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 24:
{
if (AISMessage24PartAImpl.isTypeA(sb))
{
int diff = AISMessage24PartAImpl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage24PartAImpl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage24PartAImpl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
}
else if (AISMessage24PartBImpl.isTypeB(sb))
{
int diff = AISMessage24PartBImpl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage24PartBImpl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage24PartBImpl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 25:
{
int diff = AISMessage25Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage25Impl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage25Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 26:
{
int diff = AISMessage26Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage26Impl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage26Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
case 27:
{
int diff = AISMessage27Impl.differenceInBits (sb);
assert (diff != message.getNrOfFillBits()); // message violates standard
if (diff >= 0)
{
sb.setNrOfFillBits(diff);
assert(AISMessage27Impl.validLength(sb.length())); // message changed to adhere to standard
retval = new AISMessage27Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, sb.length()));
}
else
{
//no hypothesis
retval = new AISMessageImpl(sb, provenance);
retval.AddAnnotation(annotation);
}
break;
}
default:{
return new AISMessageUnknownMessageIdImpl(sb, provenance);
}
}
assert (retval != null);
return retval;
}
private static AISMessageImpl GuessMessageIdBasedOnLength(Sixbit sb, VDMMessageProvenance provenance, AISInconsistentLengthForTypeAnnotation annotation)
{
AISMessageImpl retval = null;
switch (sb.length())
{
case 168:
{
/* AisMessagePositionReport is most occurring message.
* We assume that a message outside the specification with this length is a PositionReport
* We have chosen type 01 as implementation there of
*/
int assumedMessageId = 1;
AISMessageImpl.setMessageID(sb, assumedMessageId);
assert(AISMessageImpl.getMessageID(sb) == assumedMessageId);
retval = new AISMessage01Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, 168));
break;
}
case 312:
{
/* Message of type 19 have the relatively unique length of 312
* We assume that a message outside the specification with this length is of Type 19
*/
int assumedMessageId = 19;
AISMessageImpl.setMessageID(sb, assumedMessageId);
assert(AISMessageImpl.getMessageID(sb) == assumedMessageId);
retval = new AISMessage19Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, 312));
break;
}
case 424:
{
/* Message of type 5 have the relatively unique length of 424
* We assume that a message outside the specification with this length is of Type 05
*/
int assumedMessageId = 5;
AISMessageImpl.setMessageID(sb, assumedMessageId);
assert(AISMessageImpl.getMessageID(sb) == assumedMessageId);
retval = new AISMessage05Impl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(assumedMessageId, 424));
break;
}
}
return retval;
}
private static AISMessageImpl GuessPartIdBasedOnLength(Sixbit sb, VDMMessageProvenance provenance, AISInconsistentLengthForTypeAnnotation annotation) {
AISMessageImpl retval = null;
int messageid = AISMessageImpl.getMessageID(sb);
if (messageid == 24)
{
if (sb.length() == AISMessage24PartAImpl.LENGTHPartA)
{
AISMessage24Impl.setPart(sb, 0);
assert(AISMessage24PartAImpl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage24PartAImpl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(messageid, sb.length())); //TODO: include partId in hypothesis
}
else if (sb.length() == AISMessage24PartBImpl.LENGTHPartB)
{
AISMessage24Impl.setPart(sb, 1);
assert(AISMessage24PartBImpl.valid(sb)); // message changed to adhere to standard
retval = new AISMessage24PartBImpl(sb, provenance);
retval.AddAnnotation(annotation);
retval.AddAnnotation(new AISHypothesisAnnotation(messageid, sb.length())); //TODO: include partId in hypothesis
}
}
return retval;
}
static public AISMessage getAISMessage(VDMMessage message) {
Sixbit sb = new Sixbit(message.getMessage(), message.getNrOfFillBits());
VDMMessageProvenance provenance = message.getProvenance();
if (sb.length() < 38)
{
//Message too short according to standard for any message type
return new AISMessageIllegalImpl(sb, provenance); // the errors are logged here
}
else
{
AISMessageImpl retval = null;
retval = getAISMessageWithinSpecification(sb, provenance);
if (retval == null)
{
/* What to do with message outside specification?
* Anything can be wrong: including the messageId, the NrOfFillbits, and the length.
* How to correct this error?
*
* We use the strategy
* 1. Can PartId made consistent with length and messageId?
* 2. Classify based on uniqueness of length and frequency of occurrence of particular messages.
* 3. Assume messageId is correct, when more bits (incl. fill bits) are available than needed, parse message (assumption: we should ignore the trailing bits [and not the first bits])
* 4. TODO: Assume messageId is correct, when bits are missing, either parse conditionally or add "default" bits. (last option seems preferable: least changes to interface)
*/
int originalMessageId = AISMessageImpl.getMessageID(sb);
int originalLength = sb.length();
AISInconsistentLengthForTypeAnnotation annotation = new AISInconsistentLengthForTypeAnnotation(originalMessageId, originalLength);
retval = GuessPartIdBasedOnLength(sb, provenance, annotation);
if (retval == null)
{
retval = GuessMessageIdBasedOnLength(sb, provenance, annotation);
if (retval == null)
{
retval = AssumeMessageIdIsCorrect(message, sb, provenance, annotation);
}
}
assert (retval != null);
}
return retval;
}
}
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