/// <summary>
/// Performs the inverse transfrom from a single coordinate of linear units to the same coordinate in geodetic units
/// </summary>
/// <param name="xy">The double linear input x and y values organized into a 1 dimensional array</param>
/// <param name="lp">The double geodetic output lambda and phi values organized into a 1 dimensional array</param>
protected override void EllipticalInverse(double[] xy, double[] lp)
{
double arg = _ml0 + xy[Y] / K0;
lp[Phi] = MeridionalDistance.AngularDistance(_ml0 + xy[Y] / K0, Es, _en);
if (Math.Abs(lp[Phi]) >= HalfPi)
{
lp[Phi] = xy[Y] < 0 ? -HalfPi : HalfPi;
lp[Lambda] = 0;
}
else
{
double sinphi = Math.Sin(lp[Phi]);
double cosphi = Math.Cos(lp[Phi]);
double t = Math.Abs(cosphi) > 1e-10 ? sinphi / cosphi : 0;
double n = _esp * cosphi * cosphi;
double con;
double d = xy[X] * Math.Sqrt(con = 1 - Es * sinphi * sinphi) / K0;
con *= t;
t *= t;
double ds = d * d;
lp[Phi] -= (con * ds / (1 - Es)) * FC2 * (1 -
ds * FC4 * (5 + t * (3 - 9 * n) + n * (1 - 4 * n) -
ds * FC6 * (61 + t * (90 - 252 * n +
45 * t) + 46 * n
- ds * FC8 * (1385 + t * (3633 + t * (4095 + 1574 * t))))));
lp[Lambda] = d * (FC1 -
ds * FC3 * (1 + 2 * t + n -
ds * FC5 * (5 + t * (28 + 24 * t + 8 * n) + 6 * n
- ds * FC7 * (61 + t * (662 + t * (1320 + 720 * t)))))) / cosphi;
}
}
/// <summary>
/// Initializes the transform using the parameters from the specified coordinate system information
/// </summary>
/// <param name="projInfo">A ProjectionInfo class contains all the standard and custom parameters needed to initialize this transform</param>
protected override void OnInit(ProjectionInfo projInfo)
{
if (Es != 0)
{
_en = MeridionalDistance.GetEN(Es);
if (_en == null)
{
throw new ProjectionException(0);
}
_ml0 = MeridionalDistance.MeridionalLength(Phi0, Math.Sin(Phi0), Math.Cos(Phi0), _en);
_esp = Es / (1 - Es);
}
else
{
_esp = K0;
_ml0 = .5 * _esp;
}
}
/// <summary>
/// The forward transform where the spheroidal model of the earth has a flattening factor,
/// matching more closely with the oblique spheroid of the actual earth
/// </summary>
/// <param name="lp">The double values for geodetic lambda and phi organized into a one dimensional array</param>
/// <param name="xy">The double values for linear x and y organized into a one dimensional array</param>
protected override void EllipticalForward(double[] lp, double[] xy)
{
/*
* Fail if our longitude is more than 90 degrees from the
* central meridian since the results are essentially garbage.
* Is error -20 really an appropriate return value?
*
* http://trac.osgeo.org/proj/ticket/5
*/
if (lp[Lambda] < -HalfPi || lp[Lambda] > HalfPi)
{
xy[X] = double.NaN;
xy[Y] = double.NaN;
//xy[X] = double.PositiveInfinity;
//xy[Y] = double.PositiveInfinity;
//throw new ProjectionException(14);
}
else
{
double sinphi = Math.Sin(lp[Phi]);
double cosphi = Math.Cos(lp[Phi]);
double t = Math.Abs(cosphi) > 1E-10 ? sinphi / cosphi : 0;
t *= t;
double al = cosphi * lp[Lambda];
double als = al * al;
al /= Math.Sqrt(1 - Es * sinphi * sinphi);
double n = _esp * cosphi * cosphi;
xy[X] = K0 * al * (FC1 +
FC3 * als * (1 - t + n +
FC5 * als * (5 + t * (t - 18) + n * (14 - 58 * t) +
FC7 * als * (61 + t * (t * (179 - t) - 479)))));
xy[Y] = K0 * (MeridionalDistance.MeridionalLength(lp[Phi], sinphi, cosphi, _en) - _ml0 +
sinphi * al * lp[Lambda] * FC2 * (1 +
FC4 * als * (5 - t + n * (9 + 4 * n) +
FC6 * als * (61 + t * (t - 58) + n * (270 - 330 * t) +
FC8 * als * (1385 + t * (t * (543 - t) - 3111))))));
}
}
/// <summary>
///
/// </summary>
/// <param name="arg"></param>
/// <param name="es"></param>
/// <param name="en"></param>
/// <returns></returns>
public static double InvMlfn(double arg, double es, double[] en)
{
return(MeridionalDistance.AngularDistance(arg, es, en));
}
/// <summary>
/// Meridonal length function
/// </summary>
/// <param name="phi"></param>
/// <param name="sphi"></param>
/// <param name="cphi"></param>
/// <param name="en"></param>
/// <returns></returns>
public static double Mlfn(double phi, double sphi, double cphi, double[] en)
{
return(MeridionalDistance.MeridionalLength(phi, sphi, cphi, en));
}
/// <summary>
/// Obtains the EN parameters for the Meridional distance
/// </summary>
/// <param name="es"></param>
/// <returns></returns>
public static double[] Enfn(double es)
{
return(MeridionalDistance.GetEN(es));
}
