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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 java.text.DecimalFormat;

import nl.esi.metis.aisparser.AISMessageClassBPositionReport;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsAngle12;
import nl.esi.metis.aisparser.UtilsAngle9;
import nl.esi.metis.aisparser.UtilsLatitude27;
import nl.esi.metis.aisparser.UtilsLongitude28;
import nl.esi.metis.aisparser.UtilsPositionInfo;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.UtilsTimeStamp;
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, Pierre America (Embedded Systems Institute)
 * Copyright 2008 by Brian C. Lane 
 * All Rights Reserved
 * 
 */


/** Common implementation superclass for AIS Message 18 and 19:  Standard/Extended Class B Equipment Position Report.
 *  * 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                                     8    (  39,  46)
 *  5           speedOverGround                           10    (  47,  56)
 *  6           positionAccuracy                           1    (  57,  57)
 *  7           longitude                                 28    (  58,  85)
 *  8           latitude                                  27    (  86, 112)
 *  9           courseOverGround                          12    ( 113, 124)
 * 10           trueHeading                                9    ( 125, 133)
 * 11           timeStamp                                  6    ( 134, 139)
 * 
 * @author Pierre van de Laar
 * @author Pierre America
 * @author Brian C. Lane
 */
abstract class AISMessageClassBPositionReportImpl extends AISMessageImpl implements AISMessageClassBPositionReport {

	/** The first position of the first set of spare bits. */
	protected static final int SPARE1_FROM = 39;

	/** The last position of the first set of spare bits. */
	protected static final int SPARE1_TO = 46;

	/** The value of the first set of spare bits. */
	protected int spare1;

	/** Returns the first set of spare bits.
	 * @return the value of the first set of spare bits. This should be zero.
	 */
	public int getSpare1() { return spare1; }

	/** The position of the first bit of the speed over ground. */
	protected static final int SPEEDOVERGROUND_FROM = 47;

	/** The position of the last bit of the speed over ground. */
	protected static final int SPEEDOVERGROUND_TO = 56;
	protected int speedOverGround;

	/** Returns the speed over ground.
	 * @return an integer value in the range of 0 to 1023, 
	 * representing the speed over ground in 1/10 knot steps (0-102.2 knots) 

	 * 1023 = not available 

	 * 1022 = 102.2 knots or higher
	 */
	public int getSpeedOverGround() { return speedOverGround; }

	/** The position of the position accuracy flag. */
	protected static final int POSITIONACCURACY_BITINDEX = 57;
	
	/** The value of the position accuracy flag. */
	protected boolean positionAccuracy;

	/** Returns the position accuracy.
	 * @return a boolean value representing position accuracy: 

	 * true = high (≤ 10 m) 

	 * false = low (> 10 m)
	 */
	public boolean getPositionAccuracy() { return positionAccuracy; }

	/** The position of the first bit of the longitude. */
	protected static final int LONGITUDE_FROM = 58;

	/** The position of the last bit of the longitude. */
	protected static final int LONGITUDE_TO = 85;

	/** The longitude. */
	protected double longitude;

	/** Returns the longitude. 
	 * @return a double value representing the longitude in degrees (±180°, East = positive, West = negative). 

	 * 181° = (6791AC0 hex) = not available
	 */
	public double getLongitudeInDegrees() { return longitude; }

	/** The position of the first bit of the latitude. */
	protected static final int LATITUDE_FROM = 86;

	/** The position of the last bit of the latitude. */
	protected static final int LATITUDE_TO = 112;
	
	/** The latitude */
	protected double latitude;

	/** Returns the latitude.
	 * @return a double value representing the latitude in degrees (±90°, North = positive, South = negative). 

	 *  91° = (3412140 hex) = not available
	 */
	public double getLatitudeInDegrees() { return latitude; }

	/** The position of the first bit of the course over ground. */
	protected static final int COURSEOVERGROUND_FROM = 113;

	/** The position of the last bit of the course over ground. */
	protected static final int COURSEOVERGROUND_TO = 124;

	/** The course over ground. */
	protected int courseOverGround;

	/** Returns the course over ground. This value can be analyzed further with utility class {@link UtilsCourseOverGround12}.
	 * @return an integer value representing the course over ground in 1/10° for values in the range of 0 to 3599.

	 * 3600 (E10h) = not available. 

	 * 3601 or higher should not be used
	 */
	public int getCourseOverGround() { return courseOverGround; }

	/** The position of the first bit of the true heading. */
	protected static final int TRUEHEADING_FROM = 125;

	/** The position of the last bit of the true heading. */
	protected static final int TRUEHEADING_TO = 133;

	/** The true heading. */
	protected int trueHeading;

	/** Returns the true heading.
	 * @return an integer value representing the true heading in degrees (0-359). 

	 * 511 indicates not available
	 */
	public int getTrueHeading() { return trueHeading; }

	/** The position of the first bit of the time stamp. */
	protected static final int TIMESTAMP_FROM = 134;

	/** The position of the last bit of the time stamp. */
	protected static final int TIMESTAMP_TO = 139;

	/** The time stamp. */
	protected int timeStamp;

	/** Returns the time stamp contained in the message.
	 * This can be analyzed further using utility class {@link UtilsTimeStamp}.
	 * @return an integer value representing the UTC second when the report was generated by the electronic position fixing system (EPFS) (0-59) 

	 * 60 if time stamp is not available 

	 * 61 if positioning system is in manual input mode 

	 * 62 if electronic position fixing system operates in estimated (dead reckoning) mode 

	 * 63 if the positioning system is inoperative
	 */
	public int getTimeStamp() { return timeStamp; }

	/** The value of the second set of spare bits. 
	 * Note that the number of bits differs among the subclasses. */
	protected int spare2;

	/** Returns the second set of spare bits.
	 * @return the value of the second set of spare bits. This should be zero.
	 */
	public int getSpare2() { return spare2; }

	/** The value of the RAIM flag.
	 * Note that the position in the message differs among the subclasses. */
	protected boolean raimFlag;

	/** Returns the RAIM flag, which describes the receiver autonomous integrity monitoring status of the electronic position fixing device.
	 * @return a boolean value: 

	 * false = RAIM not in use 

	 * true = RAIM in use
	 */
	public boolean getRaimFlag() { return raimFlag; }

	/** The value of the assigned mode flag.
	 * Note that the position in the message differs among the subclasses. */
	protected boolean assignedModeFlag;

	/** The format we use to format the speed over ground */
	private static final DecimalFormat SOG_FORMAT = new DecimalFormat("##0.0");

	/** Returns the assigned mode flag.
	 * @return a boolean value representing the assigned mode flag: 

	 * false = Station operating in autonomous and continuous mode 

	 * true = Station operating in assigned mode
	 */
	public boolean getAssignedModeFlag() { return assignedModeFlag; }
	
	/** Returns the speed over ground as a string.
	 * @return a string representing the speed over ground
	 */
	public String getSpeedOverGroundString() {
		String sogString;
		if (speedOverGround == 1023)
			sogString = "no SOG";
		else if (speedOverGround == 1022)
			sogString = ">=102.2";
		else
			sogString = SOG_FORMAT.format(speedOverGround / 10.0);
		return sogString;
	}

	/** Returns the true heading as a string.
	 * @return a string representing the true heading
	 */
	public String getTrueHeadingString() {
		String headingString;
		if (trueHeading == 511)
			headingString = "no heading";
		else if (trueHeading > 359)
			headingString = "invalid heading";
		else
			headingString = Integer.toString(trueHeading);
		return headingString;
	}

	/** Constructor for type 18 or 19 AIS messages.
	 * This initializes the fields that have the same positions in the message for both message types.
	 * @param content the content of the message
	 * @param provenance the provenance of the message
	 */
	public AISMessageClassBPositionReportImpl(Sixbit content, VDMMessageProvenance provenance) {
		super(content, provenance);
	    spare1 = content.getIntFromTo(SPARE1_FROM,SPARE1_TO);
	    if (!UtilsSpare.isSpareSemanticallyCorrect(spare1))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getSpare1", spare1, UtilsSpare.range));
	    }
	    speedOverGround = content.getIntFromTo(SPEEDOVERGROUND_FROM,SPEEDOVERGROUND_TO);
	    positionAccuracy = content.getBoolean(POSITIONACCURACY_BITINDEX);
	    longitude = UtilsLongitude28.toDegrees( UtilsTwosComplement.convertFrom28Bits( content.getIntFromTo(LONGITUDE_FROM,LONGITUDE_TO) ) );
	    if (!UtilsPositionInfo.isLongitudeSemanticallyCorrect(longitude))
	    {
	    	annotations.add (new AISIllegalValueAnnotation("getLongitudeInDegrees", longitude, UtilsPositionInfo.rangeLongitude));
	    }
	    latitude = UtilsLatitude27.toDegrees( UtilsTwosComplement.convertFrom27Bits( content.getIntFromTo(LATITUDE_FROM,LATITUDE_TO) ) );
	    if (!UtilsPositionInfo.isLatitudeSemanticallyCorrect(latitude))
	    {
	    	annotations.add (new AISIllegalValueAnnotation("getLatitudeInDegrees", latitude, UtilsPositionInfo.rangeLatitude));
	    }
	    courseOverGround = content.getIntFromTo(COURSEOVERGROUND_FROM,COURSEOVERGROUND_TO);
	    if (!UtilsAngle12.isAngleSemanticallyCorrect(courseOverGround))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getCourseOverGround", courseOverGround, UtilsAngle12.range));
	    }
	    trueHeading = content.getIntFromTo(TRUEHEADING_FROM,TRUEHEADING_TO);
	    if (!UtilsAngle9.isAngleSemanticallyCorrect(trueHeading))
	    {
	    	annotations.add(new AISIllegalValueAnnotation("getTrueHeading",trueHeading, UtilsAngle9.range));
	    }
	    timeStamp = content.getIntFromTo(TIMESTAMP_FROM,TIMESTAMP_TO);
	}
	
	/** Generates a String representing the AIS message. 
	 * Format: all fields are shown in the order as specified by the standard separated by the SEPARATOR string.
	 */
	@Override
	public String toString() {
		String result = super.toString();
		result += SEPARATOR + getSpeedOverGroundString();
		result += SEPARATOR + (positionAccuracy ? "high" : "low") + " accuracy";
		result += SEPARATOR + UtilsPositionInfo.longitudeToString(longitude);
		result += SEPARATOR + UtilsPositionInfo.latitudeToString(latitude);
		result += SEPARATOR + UtilsAngle12.toString(courseOverGround);
		result += SEPARATOR + getTrueHeadingString();
		result += SEPARATOR + UtilsTimeStamp.toString(timeStamp);
		return result;		
	}
}