toOsGrid method

OSRef toOsGrid([ dynamic toDatum ])

This function first converts the lat and long coordinates from the specified datum into the OSGB36 datum It then puts the new lat and long coordinates through a mathematic algorithm that produces the easting and northing references Returns an OSRef object which contains the easting and northing

Implementation

OSRef toOsGrid([dynamic toDatum]) {
  if (toDatum == null) {
    toDatum = datums["OSGB36"];
  }
  final point = convertDatum(toDatum);

  final w = radians(point.lat);
  final l = radians(point.long);

  final a = 6377563.396;
  final b = 6356256.909;
  final F0 = 0.9996012717;
  final w0 = radians(49);
  final l0 = radians(-2);
  final N0 = -100000;
  final E0 = 400000;
  final e2 = 1 - (b*b)/(a*a);
  final n = (a-b)/(a+b);
  final n2 = n*n;
  final n3 = n*n*n;

  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 Ma = (1+n+(5/4)*n2 + (5/4)*n3) * (w-w0);
  final Mb = (3*n + 3*n*n + (21/8)*n3) * math.sin(w-w0) * math.cos(w+w0);
  final Mc = ((15/8)*n2 + (15/8)*n3) * math.sin(2*(w-w0)) * math.cos(2*(w+w0));
  final Md = (35/24)*n3 * math.sin(3*(w-w0)) * math.cos(3*(w+w0));
  final M = b * F0 * (Ma - Mb + Mc - Md); //meridional arc

  final cos3w = cosw*cosw*cosw;
  final cos5w = cos3w*cosw*cosw;
  final tan2w = math.tan(w)*math.tan(w);
  final tan4w = tan2w*tan2w;

  final I = M + N0;
  final II = (v/2)*sinw*cosw;
  final III = (v/24)*sinw*cos3w*(5-tan2w+9*N2);
  final IIIA = (v/720)*sinw*cos5w*(61-58*tan2w+tan4w);
  final IV = v*cosw;
  final V = (v/6)*cos3w*(v/p-tan2w);
  final VI = (v/120) * cos5w * (5 - 18*tan2w + tan4w + 14*N2 - 58*tan2w*N2);

  final dl = l-l0;
  final dl2 = dl*dl;
  final dl3 = dl2*dl;
  final dl4 = dl3*dl;
  final dl5 = dl4*dl;
  final dl6 = dl5*dl;

  var N = I + II*dl2 + III*dl4 + IIIA*dl6;
  var E = E0 + IV*dl + V*dl3 + VI*dl5;

  N = double.parse(N.toStringAsFixed(0));
  E = double.parse(E.toStringAsFixed(0));

  OSRef ref = OSRef(E.toInt(), N.toInt());

  return ref;

}