//--------------------------------------------------------------------------
// jscoord.js
// (c) 2005 Jonathan Stott
// Amended 2006 CD9 Design
//--------------------------------------------------------------------------

function LatLng(lat, lng) {
  this.lat = lat;
  this.lng = lng;
  this.OSGB36ToWGS84 = OSGB36ToWGS84;
}

function OSRef(easting, northing) {
  this.easting  = easting;
  this.northing = northing;
  this.toLatLng = OSRefToLatLng;
}

function RefEll(maj, min) {
  this.maj = maj;
  this.min = min;
  this.ecc = ((maj * maj) - (min * min)) / (maj * maj);
}

//--------------------------------------------------------------------------
// Mathematical Functions

function sinSquared(x) {
  return Math.sin(x) * Math.sin(x);
}

function cosSquared(x) {
  return Math.cos(x) * Math.cos(x);
}

function tanSquared(x) {
  return Math.tan(x) * Math.tan(x);
}

function sec(x) {
  return 1.0 / Math.cos(x);
}
  
function deg2rad(x) {
  return x * (Math.PI / 180);
}
  
function rad2deg(x) {
  return x * (180 / Math.PI);
}
  
function chr(x) {
  var h = x.toString (16);
  if (h.length == 1)
    h = "0" + h;
  h = "%" + h;
  return unescape (h);
}
  
function ord(x) {
  var c = x.charAt(0);
  var i;
  for (i = 0; i < 256; ++ i) {
    var h = i.toString (16);
    if (h.length == 1)
      h = "0" + h;
    h = "%" + h;
    h = unescape (h);
    if (h == c)
      break;
  }
  return i;
}

//--------------------------------------------------------------------------
// Conversion Functions

function OSGB36ToWGS84() {
  var airy1830 = new RefEll(6377563.396, 6356256.909);
  var a        = airy1830.maj;
  var b        = airy1830.min;
  var eSquared = airy1830.ecc;
  var phi = deg2rad(this.lat);
  var lambda = deg2rad(this.lng);
  var v = a / (Math.sqrt(1 - eSquared * sinSquared(phi)));
  var H = 0; // height
  var x = (v + H) * Math.cos(phi) * Math.cos(lambda);
  var y = (v + H) * Math.cos(phi) * Math.sin(lambda);
  var z = ((1 - eSquared) * v + H) * Math.sin(phi);

  var tx =        446.448;
  var ty =       -124.157;
  var tz =        542.060;
  var s  =         -0.0000204894;
  var rx = deg2rad( 0.00004172222);
  var ry = deg2rad( 0.00006861111);
  var rz = deg2rad( 0.00023391666);

  var xB = tx + (x * (1 + s)) + (-rx * y)     + (ry * z);
  var yB = ty + (rz * x)      + (y * (1 + s)) + (-rx * z);
  var zB = tz + (-ry * x)     + (rx * y)      + (z * (1 + s));

  var wgs84 = new RefEll(6378137.000, 6356752.3141);
  a        = wgs84.maj;
  b        = wgs84.min;
  eSquared = wgs84.ecc;

  var lambdaB = rad2deg(Math.atan(yB / xB));
  var p = Math.sqrt((xB * xB) + (yB * yB));
  var phiN = Math.atan(zB / (p * (1 - eSquared)));
  for (var i = 1; i < 10; i++) {
    v = a / (Math.sqrt(1 - eSquared * sinSquared(phiN)));
    phiN1 = Math.atan((zB + (eSquared * v * Math.sin(phiN))) / p);
    phiN = phiN1;
  }

  var phiB = rad2deg(phiN);
    
  this.lat = phiB;
  this.lng = lambdaB;
}


function OSRefToLatLng() {
  var airy1830 = new RefEll(6377563.396, 6356256.909);
  var OSGB_F0  = 0.9996012717;
  var N0       = -100000.0;
  var E0       = 400000.0;
  var phi0     = deg2rad(49.0);
  var lambda0  = deg2rad(-2.0);
  var a        = airy1830.maj;
  var b        = airy1830.min;
  var eSquared = airy1830.ecc;
  var phi      = 0.0;
  var lambda   = 0.0;
  var E        = this.easting;
  var N        = this.northing;
  var n        = (a - b) / (a + b);
  var M        = 0.0;
  var phiPrime = ((N - N0) / (a * OSGB_F0)) + phi0;
  do {
    M =
      (b * OSGB_F0)
        * (((1 + n + ((5.0 / 4.0) * n * n) + ((5.0 / 4.0) * n * n * n))
          * (phiPrime - phi0))
          - (((3 * n) + (3 * n * n) + ((21.0 / 8.0) * n * n * n))
            * Math.sin(phiPrime - phi0)
            * Math.cos(phiPrime + phi0))
          + ((((15.0 / 8.0) * n * n) + ((15.0 / 8.0) * n * n * n))
            * Math.sin(2.0 * (phiPrime - phi0))
            * Math.cos(2.0 * (phiPrime + phi0)))
          - (((35.0 / 24.0) * n * n * n)
            * Math.sin(3.0 * (phiPrime - phi0))
            * Math.cos(3.0 * (phiPrime + phi0))));
    phiPrime += (N - N0 - M) / (a * OSGB_F0);
  } while ((N - N0 - M) >= 0.001);
  var v = a * OSGB_F0 * Math.pow(1.0 - eSquared * sinSquared(phiPrime), -0.5);
  var rho =
    a
      * OSGB_F0
      * (1.0 - eSquared)
      * Math.pow(1.0 - eSquared * sinSquared(phiPrime), -1.5);
  var etaSquared = (v / rho) - 1.0;
  var VII = Math.tan(phiPrime) / (2 * rho * v);
  var VIII =
    (Math.tan(phiPrime) / (24.0 * rho * Math.pow(v, 3.0)))
      * (5.0
        + (3.0 * tanSquared(phiPrime))
        + etaSquared
        - (9.0 * tanSquared(phiPrime) * etaSquared));
  var IX =
    (Math.tan(phiPrime) / (720.0 * rho * Math.pow(v, 5.0)))
      * (61.0
        + (90.0 * tanSquared(phiPrime))
        + (45.0 * tanSquared(phiPrime) * tanSquared(phiPrime)));
  var X = sec(phiPrime) / v;
  var XI =
    (sec(phiPrime) / (6.0 * v * v * v))
      * ((v / rho) + (2 * tanSquared(phiPrime)));
  var XII =
    (sec(phiPrime) / (120.0 * Math.pow(v, 5.0)))
      * (5.0
        + (28.0 * tanSquared(phiPrime))
        + (24.0 * tanSquared(phiPrime) * tanSquared(phiPrime)));
  var XIIA =
    (sec(phiPrime) / (5040.0 * Math.pow(v, 7.0)))
      * (61.0
        + (662.0 * tanSquared(phiPrime))
        + (1320.0 * tanSquared(phiPrime) * tanSquared(phiPrime))
        + (720.0
          * tanSquared(phiPrime)
          * tanSquared(phiPrime)
          * tanSquared(phiPrime)));
  phi =
    phiPrime
      - (VII * Math.pow(E - E0, 2.0))
      + (VIII * Math.pow(E - E0, 4.0))
      - (IX * Math.pow(E - E0, 6.0));
  lambda =
    lambda0
      + (X * (E - E0))
      - (XI * Math.pow(E - E0, 3.0))
      + (XII * Math.pow(E - E0, 5.0))
      - (XIIA * Math.pow(E - E0, 7.0));


	// create new object to return and shift to WGS84 system	 	
	var pLatLng = new LatLng(rad2deg(phi), rad2deg(lambda));;
	pLatLng.OSGB36ToWGS84();
	return pLatLng;
}