internal static LatLng OsRefToAiry1830LatLng(OsRef osref)
{
// This is deliberately ugly C#. It's ported from javascript at http://www.jstott.me.uk/jscoord/ (v1.1.1)
// The less I touch it, the less chance there is of breaking it.
var OSGB_F0 = 0.9996012717;
var N0 = -100000.0;
var E0 = 400000.0;
var phi0 = DegreesToRadians(49.0);
var lambda0 = DegreesToRadians(-2.0);
var a = Ellipsoid.Airy1830.a;
var b = Ellipsoid.Airy1830.b;
var eSquared = Ellipsoid.Airy1830.eSquared;
var phi = 0.0;
var lambda = 0.0;
var E = osref.Easting;
var N = osref.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));
return(new LatLng(RadiansToDegrees(phi), RadiansToDegrees(lambda)));
}
public double DistanceInMetresFrom(OsRef start)
{
return(Math.Pow(Math.Pow((double)_northing - start.Northing, 2.0) + Math.Pow((double)_easting - start.Easting, 2.0), 0.5));
}
// We include these here as internal methods to keep all the ported javascript trigonometry in one class.
// They are exposed as public methods of OsRef.
internal static LatLng OsRefToWGS84LatLng(OsRef osref)
{
LatLng airy1830 = OsRefToAiry1830LatLng(osref);
return(airy1830.ToWGS84());
}
