private static VincentyFormulaVariables RecalculateσUntilConvergence(IDistance distance, int maxInterations, double tolerance, VincentyFormulaVariables v)
{
for (var i = 0; i < maxInterations; i++)
{
v.Cos2σM = Math.Cos(2 * v.σ1 + v.σ);
v.Sinσ = Math.Sin(v.σ);
v.Cosσ = Math.Cos(v.σ);
v.Δσ = v.B * v.Sinσ * (v.Cos2σM + v.B / 4.0 * (v.Cosσ * (-1.0 + 2.0 * Math.Pow(v.Cos2σM, 2.0)) -
v.B / 6.0 * v.Cos2σM * (-3.0 + 4.0 * Math.Pow(v.Sinσ, 2.0)) * (-3.0 + 4.0 * Math.Pow(v.Cos2σM, 2.0))));
v.σPrevious = v.σ;
v.σ = distance.ToMeters() / (b * v.A) + v.Δσ;
var diff = Math.Abs(v.σ - v.σPrevious);
if (diff <= tolerance)
{
break;
}
}
return(v);
}
private static VincentyFormulaVariables PrepareσConvergenceLoop(IGeographicCoordinate pointA, IAngle initialBearing, IDistance distance)
{
VincentyFormulaVariables v = new VincentyFormulaVariables();
v.Sinα1 = Math.Sin(initialBearing.ToRadians());
v.Cosα1 = Math.Cos(initialBearing.ToRadians());
v.TanU1 = (1.0 - f) * Math.Tan(pointA.Latitude.Angle.ToRadians());
v.CosU1 = 1.0 / Math.Sqrt((1 + Math.Pow(v.TanU1, 2.0)));
v.SinU1 = v.TanU1 * v.CosU1;
v.σ1 = Math.Atan2(v.TanU1, v.Cosα1);
v.sinα = v.CosU1 * v.Sinα1;
v.CosSqα = 1.0 - Math.Pow(v.sinα, 2.0);
v.USquared = v.CosSqα * (Math.Pow(a, 2.0) - Math.Pow(b, 2.0)) / Math.Pow(b, 2.0);
v.A = 1 + v.USquared / 16384.0 * (4096.0 + v.USquared * (-768.0 + v.USquared * (320.0 - 175.0 * v.USquared)));
v.B = v.USquared / 1024.0 * (256.0 + v.USquared * (-128.0 + v.USquared * (74.0 - 47.0 * v.USquared)));
v.σ = distance.ToMeters() / (b * v.A);
return(v);
}
