toLatLon method

LatLong toLatLon([ dynamic datum ])

Converts the OSRef object (easting and northing given when object is created) into a latitude and longitude of a specified datum Most widely used datum in Europe is WGS84 (this is what is used by phone GPS)

Implementation

LatLong toLatLon([var datum]) {
  if (datum == null) {
    datum = this.d;
  }

  final E = easting;
  final N = northing;

  final a = 6377563.396; //Airy 1830 major semi axis
  final b = 6356256.909; //Airy 1830 minor semi axis
  final F0 = 0.9996012717; //NatGrid scale factor on central meridian
  final w0 = radians(49);
  final l0 = radians(-2);
  final N0 = -100e3;
  final E0 = 400e3;
  final e2 = 1 - (b*b)/(a*a);
  final n = (a-b)/(a+b);
  final n2 = n*n;
  final n3 = n*n*n;

  var w = w0;
  double M = 0;

  do {
    w = (N-N0-M)/(a*F0) + w;

    var Ma = (1 + n + (5/4)*n2 + (5/4)*n3) * (w-w0);
    var Mb = (3*n + 3*n*n + (21/8)*n3) * math.sin(w-w0) * math.cos(w+w0);
    var Mc = ((15/8)*n2 + (15/8)*n3) * math.sin(2*(w-w0)) * math.cos(2*(w+w0));
    var Md = (35/24)*n3 * math.sin(3*(w-w0)) * math.cos(3*(w+w0));
    M = b * F0 * (Ma - Mb + Mc - Md);
  } while ((N-N0-M).abs() >= 0.00001);

  final cosw = math.cos(w);
  final sinw = math.sin(w);
  final v = a*F0/math.sqrt(1-e2*sinw*sinw);
  final p = a*F0*(1-e2)/math.pow(1-e2*sinw*sinw, 1.5);
  final N2 = v/p-1;

  final tanw = math.tan(w);
  final tan2w = tanw*tanw;
  final tan4w = tan2w*tan2w;
  final tan6w = tan4w*tan2w;
  final secw = 1/cosw;
  final v3 = v*v*v;
  final v5 = v3*v*v;
  final v7 = v5*v*v;

  final VII = tanw/(2*p*v);
  final VIII = tanw/(24*p*v3)*(5+3*tan2w+N2-9*tan2w*N2);
  final IX = tanw/(720*p*v5)*(61+90*tan2w+45*tan4w);
  final X = secw/v;
  final XI = secw/(6*v3)*(v/p+2*tan2w);
  final XII = secw/(120*v5)*(5+28*tan2w+24*tan4w);
  final XIIA = secw/(5040*v7)*(61+662*tan2w+1320*tan4w+720*tan6w);

  final dE = (E-E0);
  final dE2 = dE*dE;
  final dE3 = dE2*dE;
  final dE4 = dE2*dE2;
  final dE5 = dE3*dE2;
  final dE6 = dE4*dE2;
  final dE7 = dE5 * dE2;
  w = w - VII*dE2 + VIII*dE4 - IX*dE6;
  final l = l0 + X*dE - XI*dE3 + XII*dE5 - XIIA*dE7;

  LatLong latLong = LatLong(degrees(w), degrees(l), 0, Datums.OSGB36);
  if (datum != Datums.OSGB36) { //if the required datum is not osgb36, then convert to the datum given
    latLong = latLong.convertDatum(datum);
    latLong = new LatLong(latLong.lat, latLong.long, latLong.height, datum);
  }

  return latLong;

}