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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.AISMessagePositionReport;
import nl.esi.metis.aisparser.Sixbit;
import nl.esi.metis.aisparser.UtilsAngle12;
import nl.esi.metis.aisparser.UtilsLatitude27;
import nl.esi.metis.aisparser.UtilsLongitude28;
import nl.esi.metis.aisparser.UtilsNavStatus;
import nl.esi.metis.aisparser.UtilsPositionInfo;
import nl.esi.metis.aisparser.UtilsRateOfTurn8;
import nl.esi.metis.aisparser.UtilsSpare;
import nl.esi.metis.aisparser.UtilsSpecialManoeuvreIndicator2;
import nl.esi.metis.aisparser.UtilsTimeStamp;
import nl.esi.metis.aisparser.UtilsAngle9;
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
*/
/** This is the base class implementation for all AIS position report messages. It implements the fields that they all have in common.
*
* Field Nr Field Name NrOf Bits (from, to)
* ------------------------------------------------------------------------
* 1 messageID 6 ( 1, 6)
* 2 repeatIndicator 2 ( 7, 8)
* 3 userID 30 ( 9, 38)
* 4 navigationalStatus 4 ( 39, 42)
* 5 rateOfTurn 8 ( 43, 50)
* 6 speedOverGround 10 ( 51, 60)
* 7 positionAccuracy 1 ( 61, 61)
* 8 longitude 28 ( 62, 89)
* 9 latitude 27 ( 90, 116)
* 10 courseOverGround 12 ( 117, 128)
* 11 trueHeading 9 ( 129, 137)
* 12 timeStamp 6 ( 138, 143)
* 13 specialManoeuvre 2 ( 144, 145)
* 14 spare 3 ( 146, 148)
* 15 raimFlag 1 ( 149, 149)
* 16 communicationState 19 ( 150, 168)
* ---- +
* (maximum) number of bits 168
*
*
* @author Pierre van de Laar
* @author Pierre America
* @author Brian C. Lane
*/
abstract class AISMessagePositionReportImpl extends AISMessageImpl implements AISMessagePositionReport {
/** The position of the first bit of the navigational status. */
private static final int NAVIGATIONALSTATUS_FROM = 39;
/** The position of the last bit of the navigational status. */
private static final int NAVIGATIONALSTATUS_TO = 42;
/** The navigational status. */
private int navigationalStatus;
/** Returns the navigational status.
* This can be further analyzed using utility class {@link UtilsNavStatus}.
* @return an integer in the range of 0 to 15
*/
public int getNavigationalStatus() { return navigationalStatus; }
/** The position of the first bit of the rate of turn. */
private static final int RATEOFTURN_FROM = 43;
/** The position of the last bit of the rate of turn. */
private static final int RATEOFTURN_TO = 50;
/** The rate of turn. */
private int rateOfTurn;
/** Returns the rate of turn.
* This value can be analyzed further with utility class {@link UtilsRateOfTurn8}.
* @return an integer value in the range of -128 to 127
*/
public int getRateOfTurn() { return rateOfTurn; }
/** The position of the first bit of the speed over ground. */
private static final int SPEEDOVERGROUND_FROM = 51;
/** The position of the last bit of the speed over ground. */
private static final int SPEEDOVERGROUND_TO = 60;
/** The speed over ground */
private 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 format we use to format the speed over ground */
private static final DecimalFormat SOG_FORMAT = new DecimalFormat("##0.0");
/** 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;
}
/** The position of the position accuracy flag */
private static final int POSITIONACCURACY_BITINDEX = 61;
/** The position accuracy flag */
private 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. */
private static final int LONGITUDE_FROM = 62;
/** The position of the last bit of the longitude. */
private static final int LONGITUDE_TO = 89;
/** The longitude. */
private double longitude;
/** Returns the longitude in degrees.
* This value can be analyzed further with utility class {@link UtilsPositionInfo}.
* @return a double value representing the longitude in degrees (±180°, East = positive, West = negative; 181° = (6791AC0 hex) = not available = default).
*/
public double getLongitudeInDegrees() { return longitude; }
/** The position of the first bit of the latitude. */
private static final int LATITUDE_FROM = 90;
/** The position of the last bit of the latitude. */
private static final int LATITUDE_TO = 116;
/** The latitude. */
private double latitude;
/** Returns the latitude in degrees.
* This value can be analyzed further with utility class {@link UtilsPositionInfo}.
* @return a double value representing the latitude in degrees (±90°, North = positive, South = negative; 91° = (3412140 hex) = not available = default).
*/
public double getLatitudeInDegrees() { return latitude; }
/** The position of the first bit of the course over ground. */
private static final int COURSEOVERGROUND_FROM = 117;
/** The position of the last bit of the course over ground. */
private static final int COURSEOVERGROUND_TO = 128;
/** The course over ground. */
private int courseOverGround;
/** Returns the course over ground.
* This value can be analyzed further with utility class {@link UtilsAngle12}.
* @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. */
private static final int TRUEHEADING_FROM = 129;
/** The position of the last bit of the true heading. */
private static final int TRUEHEADING_TO = 137;
/** The true heading. */
private 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. */
private static final int TIMESTAMP_FROM = 138;
/** The position of the last bit of the time stamp. */
private static final int TIMESTAMP_TO = 143;
/** The time stamp. */
private 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 position of the first bit of the special maneuver indicator. */
private static final int SPECIALMANOEUVRE_FROM = 144;
/** The position of the last bit of the special maneuver indicator. */
private static final int SPECIALMANOEUVRE_TO = 145;
/** The special maneuver indicator. */
private int specialManoeuvreIndicator;
/** Returns the special maneuver indicator.
* @return an integer value with the following meaning:
* 0 = not available
* 1 = not engaged in special maneuver
* 2 = engaged in special maneuver (i.e.: regional passing arrangement on Inland Waterway)
*/
public int getSpecialManoeuvre() { return specialManoeuvreIndicator; }
/** The position of the first of the spare bits. */
private static final int SPARE_FROM = 146;
/** The position of the last of the spare bits. */
private static final int SPARE_TO = 148;
/** The value of the spare bits */
private int spare;
/** Returns the spare bits.
* @return the integer value of the spare bits, which should be zero.
*/
public int getSpare() { return spare; }
/** The position of the RAIM flag */
private static final int RAIMFLAG_BITINDEX = 149;
/** The RAIM flag */
private 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 position of the first bit of the communication state (for use in subclasses). */
protected static final int COMMUNICATIONSTATE_FROM = 150;
/** The length in bytes that a valid AIS position report message 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 position report message.
* @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 position report message
*/
public static boolean validLength(int length)
{
return (length == LENGTH);
}
/**
* Return the difference in available and needed bits to parse this sixbit as an AisMessagePositionReport
* A positive difference indicates that there are more bits available than needed by the standard.
* @param sb the sixbit
* @return the difference in available and needed bits
*/
public static int differenceInBits(Sixbit sb)
{
return (sb.available() - LENGTH);
}
/** Constructs an AIS Message Position Report.
* @param content AIS content
* @param prov the provenance of the message
* @precondition validLength(content.length())
*/
protected AISMessagePositionReportImpl(Sixbit content, VDMMessageProvenance prov)
{
super(content, prov);
assert(validLength(content.length()));
navigationalStatus = content.getIntFromTo(NAVIGATIONALSTATUS_FROM,NAVIGATIONALSTATUS_TO);
if (!UtilsNavStatus.isNavStatusSemanticallyCorrect(navigationalStatus))
{
annotations.add(new AISIllegalValueAnnotation("getNavigationalStatus", navigationalStatus, UtilsNavStatus.range));
}
rateOfTurn = UtilsTwosComplement.convertFrom8Bits( content.getIntFromTo(RATEOFTURN_FROM,RATEOFTURN_TO) );
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);
specialManoeuvreIndicator = content.getIntFromTo(SPECIALMANOEUVRE_FROM,SPECIALMANOEUVRE_TO);
if (!UtilsSpecialManoeuvreIndicator2.isSpecialManoeuvreIndicatorSemanticallyCorrect(specialManoeuvreIndicator))
{
annotations.add(new AISIllegalValueAnnotation("getSpecialManoeuvre",specialManoeuvreIndicator, UtilsSpecialManoeuvreIndicator2.range));
}
spare = content.getIntFromTo(SPARE_FROM,SPARE_TO);
if (!UtilsSpare.isSpareSemanticallyCorrect(spare))
{
annotations.add(new AISIllegalValueAnnotation("getSpare", spare, UtilsSpare.range));
}
raimFlag = content.getBoolean(RAIMFLAG_BITINDEX);
}
/** 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 + UtilsNavStatus.toString(navigationalStatus);
result += SEPARATOR + UtilsRateOfTurn8.toString(rateOfTurn);
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 + UtilsAngle9.toString(trueHeading);
result += SEPARATOR + UtilsTimeStamp.toString(timeStamp);
result += SEPARATOR + UtilsSpecialManoeuvreIndicator2.toString(specialManoeuvreIndicator);
result += SEPARATOR + "RAIM " + (raimFlag ? "in use" : "not in use");
result += SEPARATOR + getCommunicationState().toString();
return result;
}
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