// origin lat/lng converted to UTM
//const OriginUtmN = 5458391.43; UTME
//const OriginUtmE = 489851.194; UTMN

var UtmZone = 10;

var originUtmN = 0;
var originUtmE = 0;

function testUtmConversions() {

// make a GLatLng at the origin
  var testGLatLng = new GLatLng(originLatitude, originLongitude);

// find the metric conversion
  var testPt = new Point3D();
  testPt.setFromGLatLngAndAlt(testGLatLng, 100);
  testPt.show('testPt'); // should show 0,0,100

// convert back to lat/lng
  var geo2 = testPt.toGLatLng(); // should show originLat/lng
  log('lat = ' + geo2.lat() + ' lng = ' + geo2.lng());

/*
log('UTM x = '+ originUtmX + ' UTM y = ' + originUtmY);  

var testGLatLng = new GLatLng(lightLat[0], lightLng[0]);

var testPt = new Point3D();
testPt.setFromGLatLngAndAlt(testGLatLng, 100);
testPt.show('testPt');

var geo2 = testPt.toGLatLng();
log('lat = ' + geo2.lat() + ' lng = ' + geo2.lng());
  */
}  
  
function findUtmOrigin() {
  var xy = new Array(2);
  var lat = degToRad(originLatitude);
  var lng = degToRad(originLongitude);
  
  LatLonToUTMXY(lat, lng, UtmZone, xy);
  
  originUtmN = xy[1];
  originUtmE = xy[0];
}

// UTM N is our +X
function UtmNToX(utmN) {
  return (utmN - originUtmN);
}

// UTM E is our -Y
function UtmEToY(utmE) {
//  return UtmY - OriginUtmY;
  return (originUtmE - utmE);
}

function XToUtmN(x) {
  return (x + originUtmN);
}

function YToUtmE(y) {
  return (originUtmE - y);
}

//function latLngToXY(lat,lng


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;

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

// 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;
}