/// <summary>
/// The forward transform from geodetic units to linear units
/// </summary>
/// <param name="lp">The array of lambda, phi coordinates</param>
/// <param name="xy">The array of x, y coordinates</param>
protected override void OnForward(double[] lp, double[] xy)
{
double t, dl1, dl2;
double sp = Math.Sin(lp[Phi]);
double cp = Math.Cos(lp[Phi]);
double z1 = Proj.Aacos(_sp1 * sp + _cp1 * cp * Math.Cos(dl1 = lp[Lambda] + _dlam2));
double z2 = Proj.Aacos(_sp2 * sp + _cp2 * cp * Math.Cos(dl2 = lp[Lambda] - _dlam2));
z1 *= z1;
z2 *= z2;
xy[X] = _r2z0 * (t = z1 - z2);
t = _z02 - t;
xy[Y] = _r2z0 * Proj.Asqrt(4 * _z02 * z2 - t * t);
if ((_ccs * sp - cp * (_cs * Math.Sin(dl1) - _sc * Math.Sin(dl2))) < 0)
{
xy[Y] = -xy[Y];
}
}
/// <summary>
/// The inverse transform from linear units to geodetic units
/// </summary>
/// <param name="xy">The double values for the input x and y values stored in an array</param>
/// <param name="lp">The double values for the output lambda and phi values stored in an array</param>
protected override void OnInverse(double[] xy, double[] lp)
{
double cz1 = Math.Cos(Proj.Hypot(xy[Y], xy[X] + _hz0));
double cz2 = Math.Cos(Proj.Hypot(xy[Y], xy[X] - _hz0));
double s = cz1 + cz2;
double d = cz1 - cz2;
lp[Lambda] = -Math.Atan2(d, (s * _thz0));
lp[Phi] = Proj.Aacos(Proj.Hypot(_thz0 * s, d) * _rhshz0);
if (xy[Y] < 0)
{
lp[Phi] = -lp[Phi];
}
/* lam--phi now in system relative to P1--P2 base equator */
double sp = Math.Sin(lp[Phi]);
double cp = Math.Cos(lp[Phi]);
lp[Phi] = Proj.Aasin(_sa * sp + _ca * cp * (s = Math.Cos(lp[Lambda] -= _lp)));
lp[Lambda] = Math.Atan2(cp * Math.Sin(lp[Lambda]), _sa * cp * s - _ca * sp) + _lamc;
}
/// <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)
{
double pp;
/* get control point locations */
double phi1 = projInfo.GetPhi1();
double lam1 = projInfo.GetLam1();
double phi2 = projInfo.GetPhi2();
double lam2 = projInfo.GetLam2();
if (phi1 == phi2 && lam1 == lam2)
{
throw new ProjectionException(-25);
}
Lam0 = Proj.Adjlon(0.5 * (lam1 + lam2));
_dlam2 = Proj.Adjlon(lam2 - lam1);
_cp1 = Math.Cos(phi1);
_cp2 = Math.Cos(phi2);
_sp1 = Math.Sin(phi1);
_sp2 = Math.Sin(phi2);
_cs = _cp1 * _sp2;
_sc = _sp1 * _cp2;
_ccs = _cp1 * _cp2 * Math.Sin(_dlam2);
_z02 = Proj.Aacos(_sp1 * _sp2 + _cp1 * _cp2 * Math.Cos(_dlam2));
_hz0 = .5 * _z02;
double A12 = Math.Atan2(_cp2 * Math.Sin(_dlam2),
_cp1 * _sp2 - _sp1 * _cp2 * Math.Cos(_dlam2));
_ca = Math.Cos(pp = Proj.Aasin(_cp1 * Math.Sin(A12)));
_sa = Math.Sin(pp);
_lp = Proj.Adjlon(Math.Atan2(_cp1 * Math.Cos(A12), _sp1) - _hz0);
_dlam2 *= .5;
_lamc = HalfPi - Math.Atan2(Math.Sin(A12) * _sp1, Math.Cos(A12)) - _dlam2;
_thz0 = Math.Tan(_hz0);
_rhshz0 = .5 / Math.Sin(_hz0);
_r2z0 = 0.5 / _z02;
_z02 *= _z02;
}
