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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.AISMessage27;
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 27 Class
 * Long Range AIS Broadcast 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	positionAccuracy                        	   1	(  39,  39)
 *  5	raimFlag                                	   1	(  40,  40)
 *  6	navigationalStatus                      	   4	(  41,  44)
 *  7	longitude                               	  18	(  45,  62)
 *  8	latitude                                	  17	(  63,  79)
 *  9	speedOverGround                         	   6	(  80,  85)
 * 10	courseOverGround                        	   9	(  86,  94)
 * 11	statusOfCurrentGNSSPosition             	   1	(  95,  95)
 * 12	spare                                   	   1	(  96,  96)
 *                                                   ---- +
 *                       (maximum) number of bits     96
 */


class AISMessage27Impl extends AISMessageImpl implements AISMessage27 {
	public static final int LENGTH = 96;
	
	public static boolean validLength(int length)
	{
		return (length == LENGTH);
	}
	
	/**
	 * 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)
	{
		return (sb.available() - LENGTH);
	}
	
	private static final int POSITIONACCURACY_BITINDEX = 39;

	private boolean positionAccuracy;
	/** positionAccuracy
	 * @return boolean value of positionAccuracy (bit 39)
	 */
	public boolean getPositionAccuracy() { return positionAccuracy; }


	private static final int RAIMFLAG_BITINDEX = 40;

	private boolean raimFlag;
	/** raimFlag
	 * @return boolean value of raimFlag (bit 40)
	 */
	public boolean getRaimFlag() { return raimFlag; }


	private static final int NAVIGATIONALSTATUS_FROM = 41;
	private static final int NAVIGATIONALSTATUS_TO = 44;

	private int navigationalStatus;
	/** navigationalStatus
	 * @return int value of navigationalStatus (4 bits [41,44])
	 */
	public int getNavigationalStatus() { return navigationalStatus; }


	private static final int LONGITUDE_FROM = 45;
	private static final int LONGITUDE_TO = 62;

	private double longitude;
	/** longitude
	 * @return double value of longitude in degrees (18 bits [45,62])
	 */
	public double getLongitudeInDegrees() { return longitude; }


	private static final int LATITUDE_FROM = 63;
	private static final int LATITUDE_TO = 79;

	private double latitude;
	/** latitude
	 * @return double value of latitude in degrees (17 bits [63,79])
	 */
	public double getLatitudeInDegrees() { return latitude; }


	private static final int SPEEDOVERGROUND_FROM = 80;
	private static final int SPEEDOVERGROUND_TO = 85;

	private int speedOverGround;
	/** speedOverGround
	 * @return int value of speedOverGround (6 bits [80,85])
	 */
	public int getSpeedOverGround() { return speedOverGround; }


	private static final int COURSEOVERGROUND_FROM = 86;
	private static final int COURSEOVERGROUND_TO = 94;

	private int courseOverGround;
	/** courseOverGround
	 * @return int value of courseOverGround (9 bits [86,94])
	 */
	public int getCourseOverGround() { return courseOverGround; }


	private static final int STATUSOFCURRENTGNSSPOSITION_BITINDEX = 95;

	private boolean statusOfCurrentGNSSPosition;
	/** statusOfCurrentGNSSPosition
	 * @return boolean value of statusOfCurrentGNSSPosition (bit 95)
	 */
	public boolean getStatusOfCurrentGNSSPosition() { return statusOfCurrentGNSSPosition; }


	private static final int SPARE_FROM = 96;
	private static final int SPARE_TO = 96;

	private int spare;
	/** spare
	 * @return int value of spare (1 bits [96,96])
	 */
	public int getSpare() { return spare; }
	
	/** AISMessage 27 constructor
	 * @param content AIS content
	 * @param prov the provenance of the message
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==27
	 */
    public AISMessage27Impl(Sixbit content, VDMMessageProvenance prov)
	{
    	super(content, prov);
    	
    	assert(validLength(content.length()));
    	assert(getMessageID() == 27);
    	
    	// According to ITU-R M.1371-4 page 135 - table 81: Repeat Indicator Always 3 
    	if (getRepeatIndicator() != 3)
    	{
    		annotations.add(new AISIllegalValueAnnotation("getRepeatIndicator", getRepeatIndicator(), "{3}"));
    	}

	    /* Parse the Message 27 */
    	positionAccuracy = content.getBoolean(POSITIONACCURACY_BITINDEX);
    	raimFlag = content.getBoolean(RAIMFLAG_BITINDEX);
    	navigationalStatus = content.getIntFromTo(NAVIGATIONALSTATUS_FROM,NAVIGATIONALSTATUS_TO);
    	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));
	    }
	    speedOverGround = content.getIntFromTo(SPEEDOVERGROUND_FROM,SPEEDOVERGROUND_TO);
    	courseOverGround = content.getIntFromTo(COURSEOVERGROUND_FROM,COURSEOVERGROUND_TO);
    	statusOfCurrentGNSSPosition = content.getBoolean(STATUSOFCURRENTGNSSPOSITION_BITINDEX);
    	spare = content.getIntFromTo(SPARE_FROM,SPARE_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare", spare, UtilsSpare.range));
	    }
	}
}