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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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package nl.esi.metis.aisparser.impl;

import nl.esi.metis.aisparser.AISMessage17;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsLatitude17;
import nl.esi.metis.aisparser.UtilsLongitude18;
import nl.esi.metis.aisparser.UtilsPositionInfo;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.UtilsTwosComplement;
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;

/** 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
 */


/** AIS Message 17
 * GNSS Broadcast binary 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	longitude                               	  18	(  41,  58)
 *  6	latitude                                	  17	(  59,  75)
 *  7	spare2                                  	   5	(  76,  80)
 *  8	messageType                             	   6	(  81,  86)
 *  9	stationID                               	  10	(  87,  96)
 * 10	zCount                                  	  13	(  97, 109)
 * 11	sequenceNumber                          	   3	( 110, 112)
 * 12	n                                       	   5	( 113, 117)
 * 13	health                                  	   3	( 118, 120)
 * 14	dgnssDataWords                          	 696	( 121, 816)
 *                                                  ---- +
 *                       (maximum) number of bits    816
 */
class AISMessage17Impl extends AISMessageImpl implements AISMessage17 {
	public static final int MINLENGTH = 80;
	public static final int STEPSIZE = 24;
	public static final int ONEELEMENTLENGTH = 144; 		//TODO: is bits without words allowed? i.e. 120
	public static final int MAXLENGTH = 816;
	
	public static boolean validLength(int length)
	{
		return (length == MINLENGTH) || 
		       ( (ONEELEMENTLENGTH <= length) && 
		    	 (length <= MAXLENGTH) && 
		    	 ((MAXLENGTH - length)%STEPSIZE == 0) );
	}
	
	/**
	 * 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 >= MAXLENGTH)
		{
			return (available - MAXLENGTH);
		}
		else if (available >= ONEELEMENTLENGTH)
		{
			return (available - ONEELEMENTLENGTH) % STEPSIZE;
		}
		else
		{
			return available - MINLENGTH;
		}
	}
	
	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 static final int LONGITUDE_FROM = 41;
	private static final int LONGITUDE_TO = 58;

	private double longitude;
	/** longitude
	 * @return double value of longitude in degrees (18 bits [41,58])
	 */
	public double getLongitudeInDegrees() { return longitude; }


	private static final int LATITUDE_FROM = 59;
	private static final int LATITUDE_TO = 75;

	private double latitude;
	/** latitude
	 * @return double value of latitude in degrees (17 bits [59,75])
	 */
	public double getLatitudeInDegrees() { return latitude; }


	private static final int SPARE2_FROM = 76;
	private static final int SPARE2_TO = 80;

	private int spare2;
	/** spare2
	 * @return int value of spare2 (5 bits [76,80])
	 */
	public int getSpare2() { return spare2; }


	private static final int MESSAGETYPE_FROM = 81;
	private static final int MESSAGETYPE_TO = 86;

	private int messageType;
	/** messageType
	 * @return int value of messageType (6 bits [81,86])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getMessageType() { return messageType; }


	private static final int STATIONID_FROM = 87;
	private static final int STATIONID_TO = 96;

	private int stationID;
	/** stationID
	 * @return int value of stationID (10 bits [87,96])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getStationID() { return stationID; }


	private static final int ZCOUNT_FROM = 97;
	private static final int ZCOUNT_TO = 109;

	private int zCount;
	/** zCount
	 * @return int value of zCount (13 bits [97,109])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getZCount() { return zCount; }


	private static final int SEQUENCENUMBER_FROM = 110;
	private static final int SEQUENCENUMBER_TO = 112;

	private int sequenceNumber;
	/** sequenceNumber
	 * @return int value of sequenceNumber (3 bits [110,112])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getSequenceNumber() { return sequenceNumber; }


	private static final int N_FROM = 113;
	private static final int N_TO = 117;

	private int n;
	/** n
	 * @return int value of n (5 bits [113,117])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getN() { return n; }


	private static final int HEALTH_FROM = 118;
	private static final int HEALTH_TO = 120;

	private int health;
	/** health
	 * @return int value of health (3 bits [118,120])
	 * @precondition getDgnssDataWords().length > 0
	 */
	public int getHealth() { return health; }


	private static final int DGNSSDATAWORDS_FROM = 121;
//	private static final int DGNSSDATAWORDS_TO = 816;

	private int[] dgnssDataWords;
	/** dgnssDataWords
	 * @return int[] value of dgnssDataWords (696 bits [121,816])
	 */
	public int[] getDgnssDataWords() { return dgnssDataWords; }
  
	/** AISMessage 17 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==17
	 */
	public AISMessage17Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 17);
		

	    spare1 = content.getIntFromTo(SPARE1_FROM,SPARE1_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare1))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare1", spare1, UtilsSpare.range));
	    }
	    longitude = UtilsLongitude18.toDegrees( UtilsTwosComplement.convertFrom18Bits( content.getIntFromTo(LONGITUDE_FROM,LONGITUDE_TO) ) );
	    if (!UtilsPositionInfo.isLongitudeSemanticallyCorrect(longitude))
	    {
	    	annotations.add (new AISIllegalValueAnnotation("getLongitudeInDegrees", longitude, UtilsPositionInfo.rangeLongitude));
	    }
	    latitude = UtilsLatitude17.toDegrees( UtilsTwosComplement.convertFrom17Bits( content.getIntFromTo(LATITUDE_FROM,LATITUDE_TO) ) );
	    if (!UtilsPositionInfo.isLatitudeSemanticallyCorrect(latitude))
	    {
	    	annotations.add (new AISIllegalValueAnnotation("getLatitudeInDegrees", latitude, UtilsPositionInfo.rangeLatitude));
	    }
	    spare2 = content.getIntFromTo(SPARE2_FROM,SPARE2_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare2))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare2", spare2, UtilsSpare.range));
	    }
	    if (content.length() > MINLENGTH )
	    {
	    	messageType = content.getIntFromTo(MESSAGETYPE_FROM,MESSAGETYPE_TO);
	    	stationID = content.getIntFromTo(STATIONID_FROM,STATIONID_TO);
	    	zCount = content.getIntFromTo(ZCOUNT_FROM,ZCOUNT_TO);
	    	sequenceNumber = content.getIntFromTo(SEQUENCENUMBER_FROM,SEQUENCENUMBER_TO);
	    	n = content.getIntFromTo(N_FROM,N_TO);
	    	//TODO: check consistency between N and (content.length()-DGNSSDATAWORDS_FROM)/STEPSIZE   	
	    	health = content.getIntFromTo(HEALTH_FROM,HEALTH_TO);
	    	dgnssDataWords = new int[(content.length()-DGNSSDATAWORDS_FROM)/STEPSIZE];
	    	for(int i = 0; i < dgnssDataWords.length; i++)
	    	{
	    		int fromIndex = i*STEPSIZE+DGNSSDATAWORDS_FROM;
	    		int toIndex = fromIndex+STEPSIZE -1;
				dgnssDataWords[i] = content.getIntFromTo( fromIndex, toIndex );
	    	}
	    }
	    else
	    {
	    	dgnssDataWords = new int[0];
	    }
	}
}