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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;

/** This class provides methods to analyze the user ID value returned by {@link AISMessage#getUserID()}.
 * @author Pierre van de Laar
 * @author Pierre America
 */
public class UtilsUserId30 {
	/** The minimum valid value for the user ID. */
	private static final long MINVALUE = 0; 		//unsigned value
	
	/** The maximum valid value for the user ID. */
	private static final long MAXVALUE = 999999999; //nine digits
	
	/** Checks whether a user ID value is semantically correct (according to the standard).
	 * 
	 * See Annex 1 paragraph 3         page 3  and
	 *     Annex 2 paragraph 3.3.7.2.1 page 40 of ITU-R M.1371-4: Only the first 9 digits should be used.
	 * @param value the user ID value as returned by {@link AISMessage#getUserID()}.
	 * @return true if the value is semantically correct.
	 */
	public static boolean isSemanticallyCorrectValue( long value )
	{
		return ( (MINVALUE <= value) && (value <= MAXVALUE ) );
	}
	
	/** Returns the region of origin (or other category) associated with the user ID (MMSI number), inferred from the first digit.
	 * See Wikipedia for more information.
	 * 
	 * @param mmsi a valid MMSI number as returned by {@link AISMessage#getUserID()}.
	 * @return a string describing the region of origin (or other category) of the transmitter of the AIS message
	 */
	public static String getOrigin (long mmsi)
	{
		int firstDigit = (int) (mmsi/100000000L); 
		switch (firstDigit)
		{
			case 0:
				return "Ship group, coast station, or group of coast stations";
			case 1:
				return "SAR aircraft";
			case 2:
				return "Europe";
			case 3:
				return "North and Central America and Caribbean";
			case 4:
				return "Asia";
			case 5:
				return "Oceana";
			case 6:
				return "Africa";
			case 7:
				return "South America";
			case 8:
				return "Assigned for regional Use";
			case 9:
				return "Nav aids or craft associated with a parent ship";
			default:	
				return "Invalid MMSI number";
		}
	}

	/** This constructor is made private to indicate that clients should not construct instances of this class. */
	private UtilsUserId30 () {
	}
}