nl.esi.metis.aisparser.impl.AISMessage18Impl 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.AISMessage18;
import nl.esi.metis.aisparser.CommunicationState;
import nl.esi.metis.aisparser.Itdma;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.Sotdma;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.annotations.AISIllegalValueAnnotation;
import nl.esi.metis.aisparser.provenance.VDMMessageProvenance;


/** Implementation of AIS Message 18: Standard Class B equipment position report.
 * Several fields are covered by the superclass {@link AISMessageClassBPositionReportImpl}.
 * Here are the remaining fields:
 *  * Field Nr     Field Name                          NrOf Bits       (from,  to)
 * ----------------------------------------------------------------------------
 * 12           spare2                                         2    ( 140, 141)
 * 13           classBUnitFlag                                 1    ( 142, 142)
 * 14           classBDisplayFlag                              1    ( 143, 143)
 * 15           classBDSCFlag                                  1    ( 144, 144)
 * 16           classBBandFlag                                 1    ( 145, 145)
 * 17           classBMessage22Flag                            1    ( 146, 146)
 * 18           assignedModeFlag                               1    ( 147, 147)
 * 19           raimFlag                                       1    ( 148, 148)
 * 20           communicationStateSelectorFlag                 1    ( 149, 149)
 * 21           communicationState                            19    ( 150, 168)
 *                                                           ---- +
 *                       (maximum) number of bits            168
 * 
 * @author Pierre America
 * @author Pierre van de Laar
 * @author Brian C. Lane
 */
class AISMessage18Impl extends AISMessageClassBPositionReportImpl implements AISMessage18 {

	/** The first position of the second set of spare bits. */
	protected static final int SPARE2_FROM = 140;

	/** The last position of the second set of spare bits.
	 * Note that this is different from type 19 messages, 
	 * and therefore not covered by the superclass {@link AISMessageClassBPositionReportImpl}.*/
	protected static final int SPARE2_TO = 141;

	/** The position of the class B unit flag. */
	private static final int CLASSBUNITFLAG_BITINDEX = 142;

	/** The value of the class B unit flag. */
	private boolean classBUnitFlag;

	/** Returns the class B unit flag, which indicates the kind of AIS unit. 
	 * @return a boolean value representing the class B unit flag: 

	 * false = Class B SOTDMA unit 

	 * true = Class B "CS" unit
	 */
	public boolean getClassBUnitFlag() { return classBUnitFlag; }

	/** The position of the class B display flag. */
	private static final int CLASSBDISPLAYFLAG_BITINDEX = 143;

	/** The value of the class B display flag. */
	private boolean classBDisplayFlag;

	/** Returns the class B display flag, which indicates whether the unit is equipped with an integrated display displaying Message 12 and 14.
	 * @return a boolean value representing the class B display flag: 

	 * false = No display available; not capable of displaying Message 12 and 14 

	 * true = Equipped with integrated display displaying Message 12 and 14
	 */
	public boolean getClassBDisplayFlag() { return classBDisplayFlag; }

	/** The position of the class B DSC flag. */
	private static final int CLASSBDSCFLAG_BITINDEX = 144;

	/** The value of the class B DSC flag. */
	private boolean classBDSCFlag;

	/** Returns the class B DSC flag, which indicates whether the unit has the digital selective calling (DSC) function.
	 * @return a boolean value representing the class B DSC flag: 

	 * false = Not equipped with DSC function 

	 * true = Equipped with DSC function (dedicated or time-shared)
	 */
	public boolean getClassBDSCFlag() { return classBDSCFlag; }

	/** The position of the class B band flag. */
	private static final int CLASSBBANDFLAG_BITINDEX = 145;

	/** The value of the class B band flag. */
	private boolean classBBandFlag;

	/** Returns the class B band flag, which indicates over which radio bands the unit can communicate.
	 * @return a boolean value representing the class B band flag: 

	 * false = Capable of operating over the upper 525 kHz band of the marine band 

	 * true = Capable of operating over the whole marine band 

	 * (irrelevant if "Class B Message 22 flag" is 0)
	 */
	public boolean getClassBBandFlag() { return classBBandFlag; }

	/** The position of the class B Message 22 flag. */
	private static final int CLASSBMESSAGE22FLAG_BITINDEX = 146;

	/** The value of the class B Message 22 flag. */
	private boolean classBMessage22Flag;

	/** Returns the class B Message 22 flag, which indicates whether the unit supports frequency management via Message 22.
	 * @return a boolean value representing the class B Message 22 flag: 

	 * false = No frequency management via Message 22, operating on AIS1, AIS2 only 

	 * true = Frequency management via Message 22
	 */
	public boolean getClassBMessage22Flag() { return classBMessage22Flag; }

	/** The position of the assigned mode flag. 
	 * Note that the position of this flag is different for type 19 messages. */
	private static final int ASSIGNEDMODEFLAG_BITINDEX = 147;

	/** The position of the RAIM flag.
	 * Note that the position of this flag is different for type 19 messages. */
	private static final int RAIMFLAG_BITINDEX = 148;

	/** The position of the communication state selector flag. */
	private static final int COMMUNICATIONSTATESELECTORFLAG_BITINDEX = 149;

	/** The value of the communication state selector flag. */
	private boolean communicationStateSelectorFlag;

	/** Returns the communication state selector flag.
	 * @return a boolean value representing the communication state selector flag: 

	 * false = SOTDMA communication state: {@link #getCommunicationState()} will return an {@link Sotdma} object. 

	 * true = ITDMA communication state: {@link #getCommunicationState()} will return an {@link Itdma} object. 

	 * (always true for Class-B "CS" units)
	 */
	public boolean getCommunicationStateSelectorFlag() { return communicationStateSelectorFlag; }

	/** The position of the first bit of the communication state */
	private static final int COMMUNICATIONSTATE_FROM = 150;
//	private static final int COMMUNICATIONSTATE_TO = 168;

	/** The communication state */
	private CommunicationState communicationState;

	/** Returns the communication state.
	 * @return the value of the communication state. 
	 * Depending on the {@linkplain #getCommunicationStateSelectorFlag communication state selector flag}, 
	 * this may be {@link Itdma} or {@link Sotdma}.
	 */
	public CommunicationState getCommunicationState() { return communicationState; }
	
	/** The length in bytes that a valid AIS message 18 should have */
	public static final int LENGTH = 168;

	/** Checks whether the given number can be the length in bytes of the contents of a valid AIS message 18.
	 * @param length an integer value representing the length of a message in bytes
	 * @return true if this can be the length of a valid AIS message 18
	 */
	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);
	}

	
	/** AISMessage 18 constructor
	 * @param content AIS content
	 * @param prov TODO
	 * @precondition validLength(content.length()) && AISMessageBase.getMessageId(content)==18
	 */
	public AISMessage18Impl(Sixbit content, VDMMessageProvenance prov)
	{
		super(content, prov);
		assert(validLength(content.length()));
		assert(getMessageID() == 18);
	
	    spare2 = content.getIntFromTo(SPARE2_FROM, SPARE2_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare2))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare2", spare2, UtilsSpare.range));
	    }
	    classBUnitFlag = content.getBoolean(CLASSBUNITFLAG_BITINDEX);
	    classBDisplayFlag = content.getBoolean(CLASSBDISPLAYFLAG_BITINDEX);
	    classBDSCFlag = content.getBoolean(CLASSBDSCFLAG_BITINDEX);
	    classBBandFlag = content.getBoolean(CLASSBBANDFLAG_BITINDEX);
	    classBMessage22Flag = content.getBoolean(CLASSBMESSAGE22FLAG_BITINDEX);
	    assignedModeFlag = content.getBoolean(ASSIGNEDMODEFLAG_BITINDEX);
	    raimFlag = content.getBoolean(RAIMFLAG_BITINDEX);
	    communicationStateSelectorFlag = content.getBoolean(COMMUNICATIONSTATESELECTORFLAG_BITINDEX);
		if (communicationStateSelectorFlag)
		{
			communicationState = new Itdma(COMMUNICATIONSTATE_FROM, content);
		}
		else
		{
			communicationState = new Sotdma(COMMUNICATIONSTATE_FROM, content);
		}	
	}

	/** Generates a String representing the AIS message. 
	 * Format: all fields are shown in the order and units as specified by the standard separated by the SEPARATOR string.
	 */
	@Override
	public String toString() {
		String result = super.toString();
		result += SEPARATOR + (classBUnitFlag ? "CS" : "SOTDMA");
		result += SEPARATOR + (classBDisplayFlag ? "with" : "no") + " display";
		result += SEPARATOR + (classBDSCFlag ? "with" : "no") + " DSC";
		result += SEPARATOR + (classBBandFlag ? "whole" : "upper") + " band";
		result += SEPARATOR + (classBMessage22Flag ? "with" : "no") + " message 22";
		result += SEPARATOR + (assignedModeFlag ? "assigned" : "autonomous") + " mode";
		result += SEPARATOR + "RAIM " + (raimFlag ? "in use" : "not in use");
		result += SEPARATOR + (communicationStateSelectorFlag ? "ITDMA" : "SOTDMA");
		result += SEPARATOR + communicationState.toString();
		return result;		
	}
}