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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;

import java.text.DecimalFormat;

public class UtilsPositionInfo {
	/** The format we use for longitude & latitude */
	private static final DecimalFormat COORD_FORMAT = new DecimalFormat("##0.000000;-##0.000000");

	
	private static final int LONGITUDE_NOTAVAILABLE = 181;

	/** Checks if the longitude value is semantically correct (according to the standard). 
	 * This means that longitude value is either within the available range as specified by the standard, 
	 * or equal to the standard value indicating unavailability.
	 * I.e. ±180° or 181° (not available).
	 * @param longitude the longitude value in degrees 
	 * @return true if the longitude is semantically correct
	 */
	//TODO: messages of type 1,2,3,4,9,11,17,18,19,21 have an explicitly default /not available value, but messages of type 27 do not. Should they NOT accept the default value as semantically correct? 
	public static boolean isLongitudeSemanticallyCorrect( double longitude )
	{
		return isLongitudeAvailable(longitude) || (longitude == LONGITUDE_NOTAVAILABLE);
	}
	
	/** Checks if the longitude value is available.
	 * For robustness against semantical violations, this is not checked by NOT(longitude == 181), but by
	 * checking whether the longitude value is within the available range as specified by the standard. 
	 * I.e. ±180°.
	 * @param longitude the longitude value in degrees
	 * @return true if the longitude is available
	 */
	public static boolean isLongitudeAvailable(double longitude)
	{
		return ( -180 <= longitude ) && ( longitude <= 180 ); 
	}
	
	/** semantically correct range of Longitude
	 * 
	 */
	public static final String rangeLongitude = "[-180.0, 180.0] + {"+ LONGITUDE_NOTAVAILABLE +"}";
	
	/** Returns the longitude as a string.
	 * @param longitude the longitude value in degrees
	 * @return a string representing the longitude
	 */
	public static String longitudeToString(double longitude) {
		String lonString;
		if (isLongitudeSemanticallyCorrect(longitude))
		{
			if (isLongitudeAvailable(longitude))
			{
				lonString = COORD_FORMAT.format(longitude);
			}
			else
			{
				lonString = "longitude not available";	
			}
		}
		else
		{
			lonString = "invalid longitude";
		}
		return lonString;
	}

	
	
	private static final int LATITUDE_NOTAVAILABLE = 91;

	/** Checks if the latitude value is semantically correct (according to the standard). 
	 * This means that latitude value is either within the available range as specified by the standard, 
	 * or equal to the standard value indicating unavailability.
	 * I.e. ±90° or 91° (not available).
	 * @param latitude the latitude value in degrees 
	 * @return true if the latitude is semantically correct
	 */
	public static boolean isLatitudeSemanticallyCorrect( double latitude )
	{
		return isLatitudeAvailable(latitude) || (latitude == LATITUDE_NOTAVAILABLE);
	}
	
	/** Checks if the latitude value is available.
	 * For robustness against semantical violations, this is not checked by NOT(latitude == 91), but by
	 * checking whether the latitude value is within the available range as specified by the standard. 
	 * I.e. ±90°.
	 * @param latitude the latitude value in degrees
	 * @return true if the latitude is available
	 */
	public static boolean isLatitudeAvailable(double latitude)
	{
		return ( -90 <= latitude ) && ( latitude <= 90 ); 
	}
	
	/** semantically correct range of Latitude
	 * 
	 */
	public static final String rangeLatitude = "[-90.0, 90.0] + {"+ LATITUDE_NOTAVAILABLE +"}";
	
	/** Returns the latitude as a string.
	 * @param latitude the latitude value in degrees. 
     * @return a string representing the latitude
	 */
	public static String latitudeToString(double latitude) {
		String latString;
		if (isLatitudeSemanticallyCorrect(latitude))
		{
			if (isLatitudeAvailable(latitude))
			{
				latString = COORD_FORMAT.format(latitude);
			}
			else
			{
				latString = "latitude not available";	
			}
		}
		else
		{
			latString = "invalid latitude";
		}
		return latString;

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