utmpoint.java

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    /**
     * Returns 'N' if the latitude is equal to or above the equator,
     * 'S' if it's below.
     * 
     * @param lat The float value of the latitude.
     * 
     * @return A char value
     */
    protected char getLetterDesignator(double lat) {
        char letterDesignator = 'N';

        if (lat < 0) {
            letterDesignator = 'S';
        }

        return letterDesignator;
    }

    /**
     * Converts UTM coords to lat/long given an ellipsoid given an
     * instance of UTMPoint.
     * 
     * @param utm_point A UTMPoint instance.
     * @param ellip a ellipsoid definition.
     * @param llpoint a LatLonPoint, if you want it to be filled in
     *        with the results. If null, a new LatLonPoint will be
     *        allocated.
     * @return A LatLonPoint class instance containing the lat/long
     *         value, or <code>null</code> if conversion failed. If
     *         you pass in a LatLonPoint, it will be returned as well,
     *         if successful.
     */
    public static LatLonPoint UTMtoLL(UTMPoint utm_point, Ellipsoid ellip,
                                      LatLonPoint llpoint) {
        return UTMtoLL(ellip,
                utm_point.northing,
                utm_point.easting,
                utm_point.zone_number,
                utm_point.zone_letter,
                llpoint);
    }

    /**
     * Converts UTM coords to lat/long given an ellipsoid. This is a
     * convenience class where the Zone can be specified as a single
     * string eg."61N" which is then broken down into the ZoneNumber
     * and ZoneLetter.
     * 
     * @param ellip an ellipsoid definition.
     * @param UTMNorthing A float value for the northing to be
     *        converted.
     * @param UTMEasting A float value for the easting to be
     *        converted.
     * @param UTMZone A String value for the UTM zone eg."61N".
     * @param llpoint a LatLonPoint, if you want it to be filled in
     *        with the results. If null, a new LatLonPoint will be
     *        allocated.
     * @return A LatLonPoint class instance containing the lat/long
     *         value, or <code>null</code> if conversion failed. If
     *         you pass in a LatLonPoint, it will be returned as well,
     *         if successful.
     */
    public static LatLonPoint UTMtoLL(Ellipsoid ellip, float UTMNorthing,
                                      float UTMEasting, String UTMZone,
                                      LatLonPoint llpoint) {

        //without the zone we can't calculate the Lat and Long
        if (UTMZone == null || UTMZone.equals("")) {
            return null;
        }

        int ZoneNumber = 1;
        char ZoneLetter = 'N'; //northern hemisphere by default if no
                               // character is found

        //Break out the Zone number and zone letter from the UTMZone
        //string We assume the string is a valid zone with a number
        //followed by a zone letter If there is no Letter we assume
        //that it's the Northern hemisphere
        int ln = UTMZone.length() - 1;
        if (ln > 0) {
            //If it's Zero then there is only one character and it
            // must be the Zone number
            ZoneLetter = UTMZone.charAt(ln);
            if (!Character.isLetter(ZoneLetter)) {
                //No letter so assume it's missing & default to 'N'
                ZoneLetter = 'N';
                ln++;
            }
        }

        //convert the number but catch the exception if it's not
        // valid
        try {
            ZoneNumber = Integer.parseInt(UTMZone.substring(0, ln));
        } catch (NumberFormatException nfe) {
            return null;
        }

        return UTMtoLL(ellip,
                UTMNorthing,
                UTMEasting,
                ZoneNumber,
                ZoneLetter,
                llpoint);
    }

    /**
     * Converts UTM coords to lat/long given an ellipsoid. This is a
     * convenience class where the exact Zone letter is not known.
     * Instead only the hemisphere needs to be indicated.
     * 
     * @param ellip an ellipsoid definition.
     * @param UTMNorthing A float value for the northing to be
     *        converted.
     * @param UTMEasting A float value for the easting to be
     *        converted.
     * @param ZoneNumber An int value indicating the float number.
     * @param isNorthern A boolean which is true for the northern
     *        hemisphere otherwise false for the southern.
     * @param llpoint a LatLonPoint, if you want it to be filled in
     *        with the results. If null, a new LatLonPoint will be
     *        allocated.
     * @return A LatLonPoint class instance containing the lat/long
     *         value, or <code>null</code> if conversion failed. If
     *         you pass in a LatLonPoint, it will be returned as well,
     *         if successful.
     */
    public static LatLonPoint UTMtoLL(Ellipsoid ellip, float UTMNorthing,
                                      float UTMEasting, int ZoneNumber,
                                      boolean isNorthern, LatLonPoint llpoint) {

        return UTMtoLL(ellip,
                UTMNorthing,
                UTMEasting,
                ZoneNumber,
                (isNorthern) ? 'N' : 'S',
                llpoint);
    }

    /**
     * Converts UTM coords to lat/long given an ellipsoid.
     * <p>
     * Equations from USGS Bulletin 1532 <br>
     * East Longitudes are positive, West longitudes are negative.
     * <br>
     * North latitudes are positive, South latitudes are negative.
     * <br>
     * 
     * @param ellip an ellipsoid definition.
     * @param UTMNorthing A float value for the northing to be
     *        converted.
     * @param UTMEasting A float value for the easting to be
     *        converted.
     * @param zoneNumber An int value specifiying the UTM zone number.
     * @param zoneLetter A char value specifying the ZoneLetter within
     *        the ZoneNumber.
     * @param llpoint a LatLonPoint, if you want it to be filled in
     *        with the results. If null, a new LatLonPoint will be
     *        allocated.
     * @return A LatLonPoint class instance containing the lat/long
     *         value, or <code>null</code> if conversion failed. If
     *         you pass in a LatLonPoint, it will be returned as well,
     *         if successful.
     */
    public static LatLonPoint UTMtoLL(Ellipsoid ellip, float UTMNorthing,
                                      float UTMEasting, int zoneNumber,
                                      char zoneLetter, LatLonPoint llpoint) {

        //check the ZoneNummber is valid
        if (zoneNumber < 0 || zoneNumber > 60) {
            return null;
        }

        double k0 = 0.9996;
        double a = ellip.radius;
        double eccSquared = ellip.eccsq;
        double eccPrimeSquared;
        double e1 = (1 - Math.sqrt(1 - eccSquared))
                / (1 + Math.sqrt(1 - eccSquared));
        double N1, T1, C1, R1, D, M;
        double LongOrigin;
        double mu, phi1Rad;

        // remove 500,000 meter offset for longitude
        double x = UTMEasting - 500000.0d; 
        double y = UTMNorthing;

        //We must know somehow if we are in the Northern or Southern
        //hemisphere, this is the only time we use the letter So even
        //if the Zone letter isn't exactly correct it should indicate
        //the hemisphere correctly
        if (zoneLetter == 'S') {
            y -= 10000000.0d;//remove 10,000,000 meter offset used
                             // for southern hemisphere
        }

        //There are 60 zones with zone 1 being at West -180 to -174
        LongOrigin = (zoneNumber - 1) * 6 - 180 + 3; //+3 puts origin
                                                     // in middle of
                                                     // zone

        eccPrimeSquared = (eccSquared) / (1 - eccSquared);

        M = y / k0;
        mu = M
                / (a * (1 - eccSquared / 4 - 3 * eccSquared * eccSquared / 64 - 5
                        * eccSquared * eccSquared * eccSquared / 256));

        phi1Rad = mu + (3 * e1 / 2 - 27 * e1 * e1 * e1 / 32) * Math.sin(2 * mu)
                + (21 * e1 * e1 / 16 - 55 * e1 * e1 * e1 * e1 / 32)
                * Math.sin(4 * mu) + (151 * e1 * e1 * e1 / 96)
                * Math.sin(6 * mu);
//        double phi1 = ProjMath.radToDeg(phi1Rad);

        N1 = a
                / Math.sqrt(1 - eccSquared * Math.sin(phi1Rad)
                        * Math.sin(phi1Rad));
        T1 = Math.tan(phi1Rad) * Math.tan(phi1Rad);
        C1 = eccPrimeSquared * Math.cos(phi1Rad) * Math.cos(phi1Rad);
        R1 = a
                * (1 - eccSquared)
                / Math.pow(1 - eccSquared * Math.sin(phi1Rad)
                        * Math.sin(phi1Rad), 1.5);
        D = x / (N1 * k0);

        double lat = phi1Rad
                - (N1 * Math.tan(phi1Rad) / R1)
                * (D
                        * D
                        / 2
                        - (5 + 3 * T1 + 10 * C1 - 4 * C1 * C1 - 9 * eccPrimeSquared)
                        * D * D * D * D / 24 + (61 + 90 * T1 + 298 * C1 + 45
                        * T1 * T1 - 252 * eccPrimeSquared - 3 * C1 * C1)
                        * D * D * D * D * D * D / 720);
        lat = ProjMath.radToDeg(lat);

        double lon = (D - (1 + 2 * T1 + C1) * D * D * D / 6 + (5 - 2 * C1 + 28
                * T1 - 3 * C1 * C1 + 8 * eccPrimeSquared + 24 * T1 * T1)
                * D * D * D * D * D / 120)
                / Math.cos(phi1Rad);
        lon = LongOrigin + ProjMath.radToDeg(lon);
        if (llpoint != null) {
            llpoint.setLatLon((float) lat, (float) lon);
            return llpoint;
        } else {
            return new LatLonPoint((float) lat, (float) lon);
        }
    }
    
    /**
     * Find zone number based on the given latitude and longitude in *degrees*.
     * 
     * @param lat
     * @param lon
     * @return
     */
    public static int getZoneNumber(double lat, double lon) {
        int zoneNumber = (int) ((lon + 180) / 6) + 1;

        //Make sure the longitude 180.00 is in Zone 60
        if (lon == 180) {
            zoneNumber = 60;
        }

        // Special zone for Norway
        if (lat >= 56.0f && lat < 64.0f && lon >= 3.0f && lon < 12.0f) {
            zoneNumber = 32;
        }

        // Special zones for Svalbard
        if (lat >= 72.0f && lat < 84.0f) {
            if (lon >= 0.0f && lon < 9.0f)
                zoneNumber = 31;
            else if (lon >= 9.0f && lon < 21.0f)
                zoneNumber = 33;
            else if (lon >= 21.0f && lon < 33.0f)
                zoneNumber = 35;
            else if (lon >= 33.0f && lon < 42.0f)
                zoneNumber = 37;
        }
        
        return zoneNumber;
    }


}