/*
 Copyright 1997-1998 by Charles L. Taylor
 http://home.hiwaay.net/~taylorc/toolbox/geography/geoutm.html
 */

var pi = 3.14159265358979;

/* Ellipsoid model constants (actual values here are for WGS84) */
var sm_a = 6378137.0;
var sm_b = 6356752.314;
var sm_EccSquared = 6.69437999013e-03;

var UTMScaleFactor = 0.9996;

/*
 * DegToRad
 *
 * Converts degrees to radians.
 *
 */
function DegToRad(deg)
{
    return (deg / 180.0 * pi)
}

/*
 * RadToDeg
 *
 * Converts radians to degrees.
 *
 */
function RadToDeg(rad)
{
    return (rad / pi * 180.0)
}


/*
 * ArcLengthOfMeridian
 *
 * Computes the ellipsoidal distance from the equator to a point at a
 * given latitude.
 *
 * Reference: Hoffmann-Wellenhof, B., Lichtenegger, H., and Collins, J.,
 * GPS: Theory and Practice, 3rd ed.  New York: Springer-Verlag Wien, 1994.
 *
 * Inputs:
 *     phi - Latitude of the point, in radians.
 *
 * Globals:
 *     sm_a - Ellipsoid model major axis.
 *     sm_b - Ellipsoid model minor axis.
 *
 * Returns:
 *     The ellipsoidal distance of the point from the equator, in meters.
 *
 */
function ArcLengthOfMeridian(phi)
{
    var alpha, beta, gamma, delta, epsilon, n;
    var result;

    /* Precalculate n */
    n = (sm_a - sm_b) / (sm_a + sm_b);

    /* Precalculate alpha */
    alpha = ((sm_a + sm_b) / 2.0)
            * (1.0 + (Math.pow(n, 2.0) / 4.0) + (Math.pow(n, 4.0) / 64.0));

    /* Precalculate beta */
    beta = (-3.0 * n / 2.0) + (9.0 * Math.pow(n, 3.0) / 16.0)
            + (-3.0 * Math.pow(n, 5.0) / 32.0);

    /* Precalculate gamma */
    gamma = (15.0 * Math.pow(n, 2.0) / 16.0)
            + (-15.0 * Math.pow(n, 4.0) / 32.0);

    /* Precalculate delta */
    delta = (-35.0 * Math.pow(n, 3.0) / 48.0)
            + (105.0 * Math.pow(n, 5.0) / 256.0);

    /* Precalculate epsilon */
    epsilon = (315.0 * Math.pow(n, 4.0) / 512.0);

    /* Now calculate the sum of the series and return */
    result = alpha
            * (phi + (beta * Math.sin(2.0 * phi))
            + (gamma * Math.sin(4.0 * phi))
            + (delta * Math.sin(6.0 * phi))
            + (epsilon * Math.sin(8.0 * phi)));

    return result;
}


/*
 * UTMCentralMeridian
 *
 * Determines the central meridian for the given UTM zone.
 *
 * Inputs:
 *     zone - An integer value designating the UTM zone, range [1,60].
 *
 * Returns:
 *   The central meridian for the given UTM zone, in radians, or zero
 *   if the UTM zone parameter is outside the range [1,60].
 *   Range of the central meridian is the radian equivalent of [-177,+177].
 *
 */
function UTMCentralMeridian(zone)
{
    var cmeridian;

    cmeridian = DegToRad(-183.0 + (zone * 6.0));

    return cmeridian;
}


/*
 * FootpointLatitude
 *
 * Computes the footpoint latitude for use in converting transverse
 * Mercator coordinates to ellipsoidal coordinates.
 *
 * Reference: Hoffmann-Wellenhof, B., Lichtenegger, H., and Collins, J.,
 *   GPS: Theory and Practice, 3rd ed.  New York: Springer-Verlag Wien, 1994.
 *
 * Inputs:
 *   y - The UTM northing coordinate, in meters.
 *
 * Returns:
 *   The footpoint latitude, in radians.
 *
 */
function FootpointLatitude(y)
{
    var y_, alpha_, beta_, gamma_, delta_, epsilon_, n;
    var result;

    /* Precalculate n (Eq. 10.18) */
    n = (sm_a - sm_b) / (sm_a + sm_b);

    /* Precalculate alpha_ (Eq. 10.22) */
    /* (Same as alpha in Eq. 10.17) */
    alpha_ = ((sm_a + sm_b) / 2.0)
            * (1 + (Math.pow(n, 2.0) / 4) + (Math.pow(n, 4.0) / 64));

    /* Precalculate y_ (Eq. 10.23) */
    y_ = y / alpha_;

    /* Precalculate beta_ (Eq. 10.22) */
    beta_ = (3.0 * n / 2.0) + (-27.0 * Math.pow(n, 3.0) / 32.0)
            + (269.0 * Math.pow(n, 5.0) / 512.0);

    /* Precalculate gamma_ (Eq. 10.22) */
    gamma_ = (21.0 * Math.pow(n, 2.0) / 16.0)
            + (-55.0 * Math.pow(n, 4.0) / 32.0);

    /* Precalculate delta_ (Eq. 10.22) */
    delta_ = (151.0 * Math.pow(n, 3.0) / 96.0)
            + (-417.0 * Math.pow(n, 5.0) / 128.0);

    /* Precalculate epsilon_ (Eq. 10.22) */
    epsilon_ = (1097.0 * Math.pow(n, 4.0) / 512.0);

    /* Now calculate the sum of the series (Eq. 10.21) */
    result = y_ + (beta_ * Math.sin(2.0 * y_))
            + (gamma_ * Math.sin(4.0 * y_))
            + (delta_ * Math.sin(6.0 * y_))
            + (epsilon_ * Math.sin(8.0 * y_));

    return result;
}


/*
 * MapLatLonToXY
 *
 * Converts a latitude/longitude pair to x and y coordinates in the
 * Transverse Mercator projection.  Note that Transverse Mercator is not
 * the same as UTM; a scale factor is required to convert between them.
 *
 * Reference: Hoffmann-Wellenhof, B., Lichtenegger, H., and Collins, J.,
 * GPS: Theory and Practice, 3rd ed.  New York: Springer-Verlag Wien, 1994.
 *
 * Inputs:
 *    phi - Latitude of the point, in radians.
 *    lambda - Longitude of the point, in radians.
 *    lambda0 - Longitude of the central meridian to be used, in radians.
 *
 * Outputs:
 *    xy - A 2-element array containing the x and y coordinates
 *         of the computed point.
 *
 * Returns:
 *    The function does not return a value.
 *
 */
function MapLatLonToXY(phi, lambda, lambda0, xy)
{
    var N, nu2, ep2, t, t2, l;
    var l3coef, l4coef, l5coef, l6coef, l7coef, l8coef;
    var tmp;

    /* Precalculate ep2 */
    ep2 = (Math.pow(sm_a, 2.0) - Math.pow(sm_b, 2.0)) / Math.pow(sm_b, 2.0);

    /* Precalculate nu2 */
    nu2 = ep2 * Math.pow(Math.cos(phi), 2.0);

    /* Precalculate N */
    N = Math.pow(sm_a, 2.0) / (sm_b * Math.sqrt(1 + nu2));

    /* Precalculate t */
    t = Math.tan(phi);
    t2 = t * t;
    tmp = (t2 * t2 * t2) - Math.pow(t, 6.0);

    /* Precalculate l */
    l = lambda - lambda0;

    /* Precalculate coefficients for l**n in the equations below
     so a normal human being can read the expressions for easting
     and northing
     -- l**1 and l**2 have coefficients of 1.0 */
    l3coef = 1.0 - t2 + nu2;

    l4coef = 5.0 - t2 + 9 * nu2 + 4.0 * (nu2 * nu2);

    l5coef = 5.0 - 18.0 * t2 + (t2 * t2) + 14.0 * nu2
            - 58.0 * t2 * nu2;

    l6coef = 61.0 - 58.0 * t2 + (t2 * t2) + 270.0 * nu2
            - 330.0 * t2 * nu2;

    l7coef = 61.0 - 479.0 * t2 + 179.0 * (t2 * t2) - (t2 * t2 * t2);

    l8coef = 1385.0 - 3111.0 * t2 + 543.0 * (t2 * t2) - (t2 * t2 * t2);

    /* Calculate easting (x) */
    xy[0] = N * Math.cos(phi) * l
            + (N / 6.0 * Math.pow(Math.cos(phi), 3.0) * l3coef * Math.pow(l, 3.0))
            + (N / 120.0 * Math.pow(Math.cos(phi), 5.0) * l5coef * Math.pow(l, 5.0))
            + (N / 5040.0 * Math.pow(Math.cos(phi), 7.0) * l7coef * Math.pow(l, 7.0));

    /* Calculate northing (y) */
    xy[1] = ArcLengthOfMeridian(phi)
            + (t / 2.0 * N * Math.pow(Math.cos(phi), 2.0) * Math.pow(l, 2.0))
            + (t / 24.0 * N * Math.pow(Math.cos(phi), 4.0) * l4coef * Math.pow(l, 4.0))
            + (t / 720.0 * N * Math.pow(Math.cos(phi), 6.0) * l6coef * Math.pow(l, 6.0))
            + (t / 40320.0 * N * Math.pow(Math.cos(phi), 8.0) * l8coef * Math.pow(l, 8.0));

    return;
}


/*
 * MapXYToLatLon
 *
 * Converts x and y coordinates in the Transverse Mercator projection to
 * a latitude/longitude pair.  Note that Transverse Mercator is not
 * the same as UTM; a scale factor is required to convert between them.
 *
 * Reference: Hoffmann-Wellenhof, B., Lichtenegger, H., and Collins, J.,
 *   GPS: Theory and Practice, 3rd ed.  New York: Springer-Verlag Wien, 1994.
 *
 * Inputs:
 *   x - The easting of the point, in meters.
 *   y - The northing of the point, in meters.
 *   lambda0 - Longitude of the central meridian to be used, in radians.
 *
 * Outputs:
 *   philambda - A 2-element containing the latitude and longitude
 *               in radians.
 *
 * Returns:
 *   The function does not return a value.
 *
 * Remarks:
 *   The local variables Nf, nuf2, tf, and tf2 serve the same purpose as
 *   N, nu2, t, and t2 in MapLatLonToXY, but they are computed with respect
 *   to the footpoint latitude phif.
 *
 *   x1frac, x2frac, x2poly, x3poly, etc. are to enhance readability and
 *   to optimize computations.
 *
 */
function MapXYToLatLon(x, y, lambda0, philambda)
{
    var phif, Nf, Nfpow, nuf2, ep2, tf, tf2, tf4, cf;
    var x1frac, x2frac, x3frac, x4frac, x5frac, x6frac, x7frac, x8frac;
    var x2poly, x3poly, x4poly, x5poly, x6poly, x7poly, x8poly;

    /* Get the value of phif, the footpoint latitude. */
    phif = FootpointLatitude(y);

    /* Precalculate ep2 */
    ep2 = (Math.pow(sm_a, 2.0) - Math.pow(sm_b, 2.0))
            / Math.pow(sm_b, 2.0);

    /* Precalculate cos (phif) */
    cf = Math.cos(phif);

    /* Precalculate nuf2 */
    nuf2 = ep2 * Math.pow(cf, 2.0);

    /* Precalculate Nf and initialize Nfpow */
    Nf = Math.pow(sm_a, 2.0) / (sm_b * Math.sqrt(1 + nuf2));
    Nfpow = Nf;

    /* Precalculate tf */
    tf = Math.tan(phif);
    tf2 = tf * tf;
    tf4 = tf2 * tf2;

    /* Precalculate fractional coefficients for x**n in the equations
     below to simplify the expressions for latitude and longitude. */
    x1frac = 1.0 / (Nfpow * cf);

    Nfpow *= Nf;
    /* now equals Nf**2) */
    x2frac = tf / (2.0 * Nfpow);

    Nfpow *= Nf;
    /* now equals Nf**3) */
    x3frac = 1.0 / (6.0 * Nfpow * cf);

    Nfpow *= Nf;
    /* now equals Nf**4) */
    x4frac = tf / (24.0 * Nfpow);

    Nfpow *= Nf;
    /* now equals Nf**5) */
    x5frac = 1.0 / (120.0 * Nfpow * cf);

    Nfpow *= Nf;
    /* now equals Nf**6) */
    x6frac = tf / (720.0 * Nfpow);

    Nfpow *= Nf;
    /* now equals Nf**7) */
    x7frac = 1.0 / (5040.0 * Nfpow * cf);

    Nfpow *= Nf;
    /* now equals Nf**8) */
    x8frac = tf / (40320.0 * Nfpow);

    /* Precalculate polynomial coefficients for x**n.
     -- x**1 does not have a polynomial coefficient. */
    x2poly = -1.0 - nuf2;

    x3poly = -1.0 - 2 * tf2 - nuf2;

    x4poly = 5.0 + 3.0 * tf2 + 6.0 * nuf2 - 6.0 * tf2 * nuf2
            - 3.0 * (nuf2 * nuf2) - 9.0 * tf2 * (nuf2 * nuf2);

    x5poly = 5.0 + 28.0 * tf2 + 24.0 * tf4 + 6.0 * nuf2 + 8.0 * tf2 * nuf2;

    x6poly = -61.0 - 90.0 * tf2 - 45.0 * tf4 - 107.0 * nuf2
            + 162.0 * tf2 * nuf2;

    x7poly = -61.0 - 662.0 * tf2 - 1320.0 * tf4 - 720.0 * (tf4 * tf2);

    x8poly = 1385.0 + 3633.0 * tf2 + 4095.0 * tf4 + 1575 * (tf4 * tf2);

    /* Calculate latitude */
    philambda[0] = phif + x2frac * x2poly * (x * x)
            + x4frac * x4poly * Math.pow(x, 4.0)
            + x6frac * x6poly * Math.pow(x, 6.0)
            + x8frac * x8poly * Math.pow(x, 8.0);

    /* Calculate longitude */
    philambda[1] = lambda0 + x1frac * x
            + x3frac * x3poly * Math.pow(x, 3.0)
            + x5frac * x5poly * Math.pow(x, 5.0)
            + x7frac * x7poly * Math.pow(x, 7.0);

    return;
}

/*
 * LatLonToUTMXY
 *
 * Converts a latitude/longitude pair to x and y coordinates in the
 * Universal Transverse Mercator projection.
 *
 * Inputs:
 *   lat - Latitude of the point, in radians.
 *   lon - Longitude of the point, in radians.
 *   zone - UTM zone to be used for calculating values for x and y.
 *          If zone is less than 1 or greater than 60, the routine
 *          will determine the appropriate zone from the value of lon.
 *
 * Outputs:
 *   xy - A 2-element array where the UTM x and y values will be stored.
 *
 * Returns:
 *   The UTM zone used for calculating the values of x and y.
 *
 */
function LatLonToUTMXY(lat, lon, zone, xy)
{
    MapLatLonToXY(lat, lon, UTMCentralMeridian(zone), xy);

    /* Adjust easting and northing for UTM system. */
    xy[0] = xy[0] * UTMScaleFactor + 500000.0;
    xy[1] = xy[1] * UTMScaleFactor;
    if (xy[1] < 0.0)
        xy[1] = xy[1] + 10000000.0;

    return zone;
}

/*
 * UTMXYToLatLon
 *
 * Converts x and y coordinates in the Universal Transverse Mercator
 * projection to a latitude/longitude pair.
 *
 * Inputs:
 *	x - The easting of the point, in meters.
 *	y - The northing of the point, in meters.
 *	zone - The UTM zone in which the point lies.
 *	southhemi - True if the point is in the southern hemisphere;
 *               false otherwise.
 *
 * Outputs:
 *	latlon - A 2-element array containing the latitude and
 *            longitude of the point, in radians.
 *
 * Returns:
 *	The function does not return a value.
 *
 */
function UTMXYToLatLon(x, y, zone, southhemi, latlon)
{
    var cmeridian;

    x -= 500000.0;
    x /= UTMScaleFactor;

    /* If in southern hemisphere, adjust y accordingly. */
    if (southhemi)
        y -= 10000000.0;

    y /= UTMScaleFactor;

    cmeridian = UTMCentralMeridian(zone);
    MapXYToLatLon(x, y, cmeridian, latlon);

    return;
}


/*
 * Converts longitude and latitude (WSG84) to UTM
 *
 */
function WGS84ToUTM(longitude, latitude)
{
    var xy = new Array(2);

    if (isNaN(parseFloat(longitude)))
    {
        alert("Please enter a valid longitude in the lon field.");
        return false;
    }

    lon = parseFloat(longitude);

    if ((lon < -180.0) || (180.0 <= lon))
    {
        alert("The longitude you entered is out of range.  " +
              "Please enter a number in the range [-180, 180).");
        return false;
    }

    if (isNaN(parseFloat(latitude)))
    {
        alert("Please enter a valid latitude in the lat field.");
        return false;
    }

    lat = parseFloat(latitude);

    if ((lat < -90.0) || (90.0 < lat))
    {
        alert("The latitude you entered is out of range.  " +
              "Please enter a number in the range [-90, 90].");
        return false;
    }

    // Compute the UTM zone.
    zone = Math.floor((lon + 180.0) / 6) + 1;

    zone = LatLonToUTMXY(DegToRad(lat), DegToRad(lon), zone, xy);

    obj = new Object;
    obj.x = xy[0];
    obj.y = xy[1];
    obj.zoneLongitude = zone;
    obj.zoneLatitude = getLatZone(latitude);

    return obj;
}

var posLetters = ['N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Z'];
var posDegrees = [ 0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 84]
var negLetters = [ 'A', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M'];
var negDegrees = [ -90, -84, -72, -64, -56, -48, -40, -32, -24, -16, -8 ];

/*
    ESN functions below
 */

function getLatZone(latitude)
{
    var latIndex = -2;
    var lat = parseInt(latitude);
    if (lat >= 0)
    {
        var len = posLetters.length;
        for (i = 0; i < len; i++)
        {
            if (lat == posDegrees[i])
            {
                latIndex = i;
                break;
            }

            if (lat > posDegrees[i])
            {
                continue;
            }
            else
            {
                latIndex = i - 1;
                break;
            }
        }
    }
    else
    {
        var len = negLetters.length;
        for (i = 0; i < len; i++)
        {
            if (lat == negDegrees[i])
            {
                latIndex = i;
                break;
            }
            if (lat < negDegrees[i])
            {
                latIndex = i - 1;
                break;
            }
            else
            {
                continue;
            }
        }
    }

    if (latIndex == -1)
    {
        latIndex = 0;
    }
    if (lat >= 0)
    {
        if (latIndex == -2)
        {
            latIndex = posLetters.length - 1;
        }
        return posLetters[latIndex];
    }
    else
    {
        if (latIndex == -2)
        {
            latIndex = negLetters.length - 1;
        }
        return negLetters[latIndex];
    }
}

var fakeWidthFactor = [];
fakeWidthFactor["X"] =  .55;
fakeWidthFactor["W"] =  .60;
fakeWidthFactor["V"] =  .65;
fakeWidthFactor["U"] =  .70;
fakeWidthFactor["T"] =  .75;
fakeWidthFactor["S"] =  .80;
fakeWidthFactor["R"] =  .85;
fakeWidthFactor["Q"] =  .90;
fakeWidthFactor["P"] =  .95;
fakeWidthFactor["N"] = 1.0;
fakeWidthFactor["M"] = 1.0;
fakeWidthFactor["L"] =  .95;
fakeWidthFactor["K"] =  .90;
fakeWidthFactor["J"] =  .85;
fakeWidthFactor["H"] =  .80;
fakeWidthFactor["G"] =  .75;
fakeWidthFactor["F"] =  .70;
fakeWidthFactor["E"] =  .65;
fakeWidthFactor["D"] =  .60;
fakeWidthFactor["C"] =  .55;

function getFakeWidthFactor(utmObject)
{
    return fakeWidthFactor[utmObject.zoneLatitude];
}

function isNorthernHemisphere(utmObject)
{
    return utmObject.zoneLatitude >= 'N';
}

var threeSixtyDegreesMeters = 40008285.925794;                            // meters
var eightyDegreesLatitudeMeters = threeSixtyDegreesMeters * 80.0 / 360.0; // meters
var totalLatitudeMeters = threeSixtyDegreesMeters * 164.0 / 360.0;        // from 80 S to 84 N, in meters

function UTMToXY(utmObject, canvasWitdh, canvasHeight)
{
    var gridWidth = canvasWitdh / 60;

    var yMeters = isNorthernHemisphere(utmObject)                         // is northern hemi?
            ? eightyDegreesLatitudeMeters + utmObject.y                   // if so, add 80 degrees north in meters (the origin is defined as the equator)
            : utmObject.y - (10000000.0 - eightyDegreesLatitudeMeters);   // else, the origin is defined as a point 10,000,000 metres south of the equator

    var yPixels = Math.round(yMeters / totalLatitudeMeters * canvasHeight);
    var y = canvasHeight - yPixels;                                       // invert so zero is top edge

    var multiplierLongitude = utmObject.zoneLongitude - 1;                // Horizontal (east)
    var baseX = multiplierLongitude * gridWidth;

    /* The width (in meters) of the zone at a specified degree */
    var xWidth = threeSixtyDegreesMeters / 60.0; // at the equator - this must be modified when moving away from the equator
    xWidth *= getFakeWidthFactor(utmObject);
    
    /* For the eastings, the origin is defined as a point 500,000 metres west of the central meridian
    of each longitudinal zone, giving an easting of 500,000 metres at the central meridian. */
    var centerOffsetMeters = utmObject.x < 500000.0 ? -(500000.0 - utmObject.x) : utmObject.x - 500000.0;
    var centerOffset = gridWidth * (centerOffsetMeters / xWidth);

    var pixelXOffset = (gridWidth / 2.0) + centerOffset;
    var x = Math.round(baseX + pixelXOffset);

    obj = new Object;
    obj.x = parseInt(x);
    obj.y = parseInt(y);

    return obj;
}

function testXY(longitude, latitude)
{
    // Create UTM object
    result = WGS84ToUTM(longitude, latitude);
    // Convert UTM to map pixels
    result = UTMToXY(result, 910, 455);
    alert("result: x=" + result.x + " y=" + result.y);
    return;
}