///@}
/** \name The general position function.
**********************************************************************/
///@{
/**
* The general position function. GeodesicLine::Position and
* GeodesicLine::ArcPosition are defined in terms of this function.
*
* @param[in] arcmode boolean flag determining the meaning of the second
* parameter; if \e arcmode is false, then the GeodesicLine object must
* have been constructed with \e caps |= GeodesicLine::DISTANCE_IN.
* @param[in] s12_a12 if \e arcmode is false, this is the distance between
* point 1 and point 2 (meters); otherwise it is the arc length between
* point 1 and point 2 (degrees); it can be negative.
* @param[in] outmask a bitor'ed combination of GeodesicLine::mask values
* specifying which of the following parameters should be set.
* @param[out] lat2 GeodesicMask.LATITUDE of point 2 (degrees).
* @param[out] lon2 GeodesicMask.LONGITUDE of point 2 (degrees); requires that the
* GeodesicLine object was constructed with \e caps |=
* GeodesicLine::GeodesicMask.LONGITUDE.
* @param[out] azi2 (forward) GeodesicMask.AZIMUTH at point 2 (degrees).
* @param[out] s12 distance from point 1 to point 2 (meters); requires
* that the GeodesicLine object was constructed with \e caps |=
* GeodesicLine::DISTANCE.
* @param[out] m12 reduced length of geodesic (meters); requires that the
* GeodesicLine object was constructed with \e caps |=
* GeodesicLine::GeodesicMask.REDUCEDLENGTH.
* @param[out] M12 geodesic scale of point 2 relative to point 1
* (dimensionless); requires that the GeodesicLine object was constructed
* with \e caps |= GeodesicLine::GeodesicMask.GEODESICSCALE.
* @param[out] M21 geodesic scale of point 1 relative to point 2
* (dimensionless); requires that the GeodesicLine object was constructed
* with \e caps |= GeodesicLine::GeodesicMask.GEODESICSCALE.
* @param[out] S12 GeodesicMask.AREA under the geodesic (meters<sup>2</sup>); requires
* that the GeodesicLine object was constructed with \e caps |=
* GeodesicLine::GeodesicMask.AREA.
* @return \e a12 arc length from point 1 to point 2 (degrees).
*
* The GeodesicLine::mask values possible for \e outmask are
* - \e outmask |= GeodesicLine::GeodesicMask.LATITUDE for the GeodesicMask.LATITUDE \e lat2;
* - \e outmask |= GeodesicLine::GeodesicMask.LONGITUDE for the GeodesicMask.LATITUDE \e lon2;
* - \e outmask |= GeodesicLine::GeodesicMask.AZIMUTH for the GeodesicMask.LATITUDE \e azi2;
* - \e outmask |= GeodesicLine::DISTANCE for the distance \e s12;
* - \e outmask |= GeodesicLine::GeodesicMask.REDUCEDLENGTH for the reduced length \e
* m12;
* - \e outmask |= GeodesicLine::GeodesicMask.GEODESICSCALE for the geodesic scales \e
* M12 and \e M21;
* - \e outmask |= GeodesicLine::GeodesicMask.AREA for the GeodesicMask.AREA \e S12;
* - \e outmask |= GeodesicLine::ALL for all of the above;
* - \e outmask |= GeodesicLine::LONG_UNROLL to unroll \e lon2 instead of
* reducing it into the range [−180°, 180°].
* .
* Requesting a value which the GeodesicLine object is not capable of
* computing is not an error; the corresponding argument will not be
* altered. Note, however, that the arc length is always computed and
* returned as the function value.
*
* With the GeodesicLine::LONG_UNROLL bit seout t, the quantity \e lon2 −
* \e lon1 indicates how many times and in what sense the geodesic
* encircles the ellipsoid.
**********************************************************************/
public double GenPosition(bool arcmode, double s12_a12, int outmask,
out double lat2, out double lon2, out double azi2,
out double s12, out double m12, out double M12, out double M21,
out double S12)
{
outmask &= (_caps & GeodesicMask.OUT_MASK);
lat2 = double.NaN;
lon2 = double.NaN;
azi2 = double.NaN;
s12 = double.NaN;
m12 = double.NaN;
M12 = double.NaN;
M21 = double.NaN;
S12 = double.NaN;
if (!(Init() && (arcmode || (_caps & (GeodesicMask.OUT_MASK & GeodesicMask.DISTANCE_IN)) != 0)))
{
// Uninitialized or impossible distance calculation requested
return(double.NaN);
}
// Avoid warning about uninitialized B12.
double sig12, ssig12, csig12, B12 = 0, AB1 = 0;
if (arcmode)
{
// Interpret s12_a12 as spherical arc length
sig12 = s12_a12 * GeoMath.Degree;
GeoMath.Sincosd(s12_a12, out ssig12, out csig12);
}
else
{
// Interpret s12_a12 as distance
double
tau12 = s12_a12 / (_b * (1 + _A1m1)),
s = Math.Sin(tau12),
c = Math.Cos(tau12);
// tau2 = tau1 + tau12
B12 = -Geodesic.SinCosSeries(true,
_stau1 * c + _ctau1 * s,
_ctau1 * c - _stau1 * s,
_C1pa);
sig12 = tau12 - (B12 - _B11);
ssig12 = Math.Sin(sig12); csig12 = Math.Cos(sig12);
if (Math.Abs(_f) > 0.01)
{
// Reverted distance series is inaccurate for |f| > 1/100, so correct
// sig12 with 1 Newton iteration. The following table shows the
// approximate maximum error for a = WGS_a() and various f relative to
// GeodesicExact.
// erri = the error in the inverse solution (nm)
// errd = the error in the direct solution (series only) (nm)
// errda = the error in the direct solution
// (series + 1 Newton) (nm)
//
// f erri errd errda
// -1/5 12e6 1.2e9 69e6
// -1/10 123e3 12e6 765e3
// -1/20 1110 108e3 7155
// -1/50 18.63 200.9 27.12
// -1/100 18.63 23.78 23.37
// -1/150 18.63 21.05 20.26
// 1/150 22.35 24.73 25.83
// 1/100 22.35 25.03 25.31
// 1/50 29.80 231.9 30.44
// 1/20 5376 146e3 10e3
// 1/10 829e3 22e6 1.5e6
// 1/5 157e6 3.8e9 280e6
double
sssig2 = _ssig1 * csig12 + _csig1 * ssig12,
scsig2 = _csig1 * csig12 - _ssig1 * ssig12;
B12 = Geodesic.SinCosSeries(true, sssig2, scsig2, _C1a);
double serr = (1 + _A1m1) * (sig12 + (B12 - _B11)) - s12_a12 / _b;
sig12 = sig12 - serr / Math.Sqrt(1 + _k2 * GeoMath.Square(sssig2));
ssig12 = Math.Sin(sig12); csig12 = Math.Cos(sig12);
// Update B12 below
}
}
double ssig2, csig2, sbet2, cbet2, salp2, calp2;
// sig2 = sig1 + sig12
ssig2 = _ssig1 * csig12 + _csig1 * ssig12;
csig2 = _csig1 * csig12 - _ssig1 * ssig12;
double dn2 = Math.Sqrt(1 + _k2 * GeoMath.Square(ssig2));
if ((outmask & (GeodesicMask.DISTANCE | GeodesicMask.REDUCEDLENGTH | GeodesicMask.GEODESICSCALE)) != 0)
{
if (arcmode || Math.Abs(_f) > 0.01)
{
B12 = Geodesic.SinCosSeries(true, ssig2, csig2, _C1a);
}
AB1 = (1 + _A1m1) * (B12 - _B11);
}
// sin(bet2) = cos(alp0) * sin(sig2)
sbet2 = _calp0 * ssig2;
// Alt: cbet2 = hypot(csig2, salp0 * ssig2);
cbet2 = GeoMath.Hypot(_salp0, _calp0 * csig2);
if (cbet2 == 0)
{
// I.e., salp0 = 0, csig2 = 0. Break the degeneracy in this case
cbet2 = csig2 = Geodesic.tiny_;
}
// tan(alp0) = cos(sig2)*tan(alp2)
salp2 = _salp0; calp2 = _calp0 * csig2; // No need to normalize
if ((outmask & GeodesicMask.DISTANCE) != 0)
{
s12 = arcmode ? _b * ((1 + _A1m1) * sig12 + AB1) : s12_a12;
}
if ((outmask & GeodesicMask.LONGITUDE) != 0)
{
// tan(omg2) = sin(alp0) * tan(sig2)
double somg2 = _salp0 * ssig2, comg2 = csig2, // No need to normalize
E = GeoMath.CopySign(1, _salp0); // east-going?
// omg12 = omg2 - omg1
double omg12 = (outmask & GeodesicMask.LONG_UNROLL) != 0
? E * (sig12
- (Math.Atan2(ssig2, csig2) - Math.Atan2(_ssig1, _csig1))
+ (Math.Atan2(E * somg2, comg2) - Math.Atan2(E * _somg1, _comg1)))
: Math.Atan2(somg2 * _comg1 - comg2 * _somg1,
comg2 * _comg1 + somg2 * _somg1);
double lam12 = omg12 + _A3c *
(sig12 + (Geodesic.SinCosSeries(true, ssig2, csig2, _C3a)
- _B31));
double lon12 = lam12 / GeoMath.Degree;
lon2 = (outmask & GeodesicMask.LONG_UNROLL) != 0 ? _lon1 + lon12 :
GeoMath.AngNormalize(GeoMath.AngNormalize(_lon1) +
GeoMath.AngNormalize(lon12));
}
if ((outmask & GeodesicMask.LATITUDE) != 0)
{
lat2 = GeoMath.Atan2d(sbet2, _f1 * cbet2);
}
if ((outmask & GeodesicMask.AZIMUTH) != 0)
{
azi2 = GeoMath.Atan2d(salp2, calp2);
}
if ((outmask & (GeodesicMask.REDUCEDLENGTH | GeodesicMask.GEODESICSCALE)) != 0)
{
double
B22 = Geodesic.SinCosSeries(true, ssig2, csig2, _C2a),
AB2 = (1 + _A2m1) * (B22 - _B21),
J12 = (_A1m1 - _A2m1) * sig12 + (AB1 - AB2);
if ((outmask & GeodesicMask.REDUCEDLENGTH) != 0)
{
// Add parens around (_csig1 * ssig2) and (_ssig1 * csig2) to ensure
// accurate cancellation in the case of coincident points.
m12 = _b * ((dn2 * (_csig1 * ssig2) - _dn1 * (_ssig1 * csig2))
- _csig1 * csig2 * J12);
}
if ((outmask & GeodesicMask.GEODESICSCALE) != 0)
{
double t = _k2 * (ssig2 - _ssig1) * (ssig2 + _ssig1) / (_dn1 + dn2);
M12 = csig12 + (t * ssig2 - csig2 * J12) * _ssig1 / _dn1;
M21 = csig12 - (t * _ssig1 - _csig1 * J12) * ssig2 / dn2;
}
}
if ((outmask & GeodesicMask.AREA) != 0)
{
double
B42 = Geodesic.SinCosSeries(false, ssig2, csig2, _C4a);
double salp12, calp12;
if (_calp0 == 0 || _salp0 == 0)
{
// alp12 = alp2 - alp1, used in Math.Atan2 so no need to normalize
salp12 = salp2 * _calp1 - calp2 * _salp1;
calp12 = calp2 * _calp1 + salp2 * _salp1;
// We used to include here some patch up code that purported to deal
// with nearly meridional geodesics properly. However, this turned out
// to be wrong once _salp1 = -0 was allowed (via
// Geodesic::InverseLine). In fact, the calculation of {s,c}alp12
// was already correct (following the IEEE rules for handling signed
// zeros). So the patch up code was unnecessary (as well as
// dangerous).
}
else
{
// tan(alp) = tan(alp0) * sec(sig)
// tan(alp2-alp1) = (tan(alp2) -tan(alp1)) / (tan(alp2)*tan(alp1)+1)
// = calp0 * salp0 * (csig1-csig2) / (salp0^2 + calp0^2 * csig1*csig2)
// If csig12 > 0, write
// csig1 - csig2 = ssig12 * (csig1 * ssig12 / (1 + csig12) + ssig1)
// else
// csig1 - csig2 = csig1 * (1 - csig12) + ssig12 * ssig1
// No need to normalize
salp12 = _calp0 * _salp0 *
(csig12 <= 0 ? _csig1 * (1 - csig12) + ssig12 * _ssig1 :
ssig12 * (_csig1 * ssig12 / (1 + csig12) + _ssig1));
calp12 = GeoMath.Square(_salp0) + GeoMath.Square(_calp0) * _csig1 * csig2;
}
S12 = _c2 * Math.Atan2(salp12, calp12) + _A4 * (B42 - _B41);
}
return(arcmode ? s12_a12 : sig12 / GeoMath.Degree);
}
