nl.esi.metis.aisparser.impl.AISMessage20Impl Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of EsiAisParser Show documentation

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.

The newest version!

package nl.esi.metis.aisparser.impl;

import nl.esi.metis.aisparser.AISMessage20;
import nl.esi.metis.aisparser.AISMessage20Unit;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsSpare;
/** ESI AIS Parser
 * 
 * Copyright 2011/2012 by Pierre van de Laar (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 * @author Pierre van de Laar
 * @author Brian C. Lane
 */
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;


/** AIS Message 20
 * Data Link Management Message
 * 
 * Field Nr     Field Name                          NrOf Bits   (from, to )
 * ------------------------------------------------------------------------
 *  1	messageID                               	   6	(   1,   6)
 *  2	repeatIndicator                         	   2	(   7,   8)
 *  3	userID                                  	  30	(   9,  38)
 *  4	spare1                                  	   2	(  39,  40)
 *  5	offsetNumber1                           	  12	(  41,  52)
 *  6	numberOfSlots1                          	   4	(  53,  56)
 *  7	timeOut1                                	   3	(  57,  59)
 *  8	increment1                              	  11	(  60,  70)
 *  9	offsetNumber2                           	  12	(  71,  82)
 * 10	numberOfSlots2                          	   4	(  83,  86)
 * 11	timeOut2                                	   3	(  87,  89)
 * 12	increment2                              	  11	(  90, 100)
 * 13	offsetNumber3                           	  12	( 101, 112)
 * 14	numberOfSlots3                          	   4	( 113, 116)
 * 15	timeOut3                                	   3	( 117, 119)
 * 16	increment3                              	  11	( 120, 130)
 * 17	offsetNumber4                           	  12	( 131, 142)
 * 18	numberOfSlots4                          	   4	( 143, 146)
 * 19	timeOut4                                	   3	( 147, 149)
 * 20	increment4                              	  11	( 150, 160)
 * 21	spare2                                  	   0	
 *                                                      ---- +
 *                           (maximum) number of bits    160
 */
class AISMessage20Impl extends AISMessageImpl implements AISMessage20 {
	private static final int LENGTHWITH1SLOT  =  72;
    private static final int LENGTHWITH2SLOTS = 104;
    private static final int LENGTHWITH3SLOTS = 136;
	private static final int LENGTHWITH4SLOTS = 160;
	
	public static boolean validLength(int length)
	{
		return ( (length == LENGTHWITH1SLOT ) ||
				 (length == LENGTHWITH2SLOTS) ||
				 (length == LENGTHWITH3SLOTS) ||
				 (length == LENGTHWITH4SLOTS) );
	}
	
	/**
	 * Return the difference in available and needed bits to parse this sixbit as an AISMessage
	 * A positive difference indicates that there are more bits available than needed by the standard.
	 * @param sb
	 * @return
	 */
	public static int differenceInBits(Sixbit sb)
	{
		final int available = sb.available();
		if (available >= LENGTHWITH4SLOTS)
		{
			return available - LENGTHWITH4SLOTS;
		}
		else if (available >= LENGTHWITH3SLOTS)
		{
			return available - LENGTHWITH3SLOTS;
		}
		else if (available >= LENGTHWITH2SLOTS)
		{
			return available - LENGTHWITH2SLOTS;
		} else
		{
			return available - LENGTHWITH1SLOT;
		}
	}

	private static final int SPARE1_FROM = 39;
	private static final int SPARE1_TO = 40;

	private int spare1;
	/** spare1
	 * @return int value of spare1 (2 bits [39,40])
	 */
	public int getSpare1() { return spare1; }


	private AISMessage20Unit[] units;
	/** units
	 * @return Array of AISMessage20Unit containing all units in the AIS Message
	 */
	public AISMessage20Unit[] getUnits() { return units; }


	private int spare2;
	/** spare2
	 * @return int value of spare2 (0-6 bits)
	 */
	public int getSpare2() { return spare2; }

    
	/** AISMessage 20 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==20
	 */
	public AISMessage20Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 20);

		spare1 = content.getIntFromTo(SPARE1_FROM,SPARE1_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare1))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare1", spare1, UtilsSpare.range));
	    }
		switch (content.length())
		{
			case LENGTHWITH1SLOT:
				units = new AISMessage20Unit[1];
				break;
			case LENGTHWITH2SLOTS:
				units = new AISMessage20Unit[2];
				break;
			case LENGTHWITH3SLOTS:
				units = new AISMessage20Unit[3];
				break;
			case LENGTHWITH4SLOTS:
				units = new AISMessage20Unit[4];
				break;
		}
		int offset = 41;
		for(int i=0; i < units.length; i++)
		{
			units[i] = new AISMessage20UnitImpl(offset, content);
			offset+=30;
		}
		spare2 = content.getIntFromTo(offset, content.length());
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare2))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare2", spare2, UtilsSpare.range));
	    }	}
}