albersequal.cpp

/*
 * Based on libgeotrans with the following Source Code Disclaimer:

1. The GEOTRANS source code ("the software") is provided free of charge by
the National Imagery and Mapping Agency (NIMA) of the United States
Department of Defense. Although NIMA makes no copyright claim under Title 17
U.S.C., NIMA claims copyrights in the source code under other legal regimes.
NIMA hereby grants to each user of the software a license to use and
distribute the software, and develop derivative works.

2. Warranty Disclaimer: The software was developed to meet only the internal
requirements of the U.S. National Imagery and Mapping Agency. The software
is provided "as is," and no warranty, express or implied, including but not
limited to the implied warranties of merchantability and fitness for
particular purpose or arising by statute or otherwise in law or from a
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4. Neither NIMA nor its personnel will be liable for any claims, losses, or
damages arising from or connected with the use of the software. The user
agrees to hold harmless the United States National Imagery and Mapping
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5. NIMA requests that products developed using the software credit the
source of the software with the following statement, "The product was
developed using GEOTRANS, a product of the National Imagery and Mapping
Agency and U.S. Army Engineering Research and Development Center."

6. For any products developed using the software, NIMA requires a disclaimer
that use of the software does not indicate endorsement or approval of the
product by the Secretary of Defense or the National Imagery and Mapping
Agency. Pursuant to the United States Code, 10 U.S.C. Sec. 2797, the name of
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*/

#include "map/ellipsoid.h"
#include "albersequal.h"


#define ONE_MINUS_SQR(x) (1.0 - (x) * (x))
#define ALBERS_Q(slat, one_minus_sqr_e_sin, es_sin) \
	(_one_minus_es * ((slat) / (one_minus_sqr_e_sin) - \
	(1 / (_two_e)) * log((1 - (es_sin)) / (1 + (es_sin)))))
#define ALBERS_M(clat, one_minus_sqr_e_sin) \
	((clat) / sqrt(one_minus_sqr_e_sin))


AlbersEqual::AlbersEqual(const Ellipsoid &ellipsoid, double standardParallel1,
  double standardParallel2, double latitudeOrigin, double longitudeOrigin,
  double falseEasting, double falseNorthing)
{
	double sin_lat, sin_lat1, sin_lat2, cos_lat1, cos_lat2;
	double m1, m2, sqr_m1, sqr_m2;
	double q0, q1, q2;
	double e_sin, e_sin1, e_sin2;
	double one_minus_sqr_e_sin1, one_minus_sqr_e_sin2;
	double nq0;
	double sp1, sp2;


	_latitudeOrigin = deg2rad(latitudeOrigin);
	_longitudeOrigin = deg2rad(longitudeOrigin);
	_falseEasting = falseEasting;
	_falseNorthing = falseNorthing;

	sp1 = deg2rad(standardParallel1);
	sp2 = deg2rad(standardParallel2);

	_a2 = ellipsoid.radius() * ellipsoid.radius();
	_es = ellipsoid.es();
	_e = sqrt(_es);
	_one_minus_es = 1 - _es;
	_two_e = 2 * _e;

	sin_lat = sin(_latitudeOrigin);
	e_sin = _e * sin_lat;
	q0 = ALBERS_Q(sin_lat, ONE_MINUS_SQR(e_sin), e_sin);

	sin_lat1 = sin(sp1);
	cos_lat1 = cos(sp1);
	e_sin1 = _e * sin_lat1;
	one_minus_sqr_e_sin1 = ONE_MINUS_SQR(e_sin1);
	m1 = ALBERS_M(cos_lat1, one_minus_sqr_e_sin1);
	q1 = ALBERS_Q(sin_lat1, one_minus_sqr_e_sin1, e_sin1);

	sqr_m1 = m1 * m1;
	if (fabs(sp1 - sp2) > 1.0e-10) {
		sin_lat2 = sin(sp2);
		cos_lat2 = cos(sp2);
		e_sin2 = _e * sin_lat2;
		one_minus_sqr_e_sin2 = ONE_MINUS_SQR(e_sin2);
		m2 = ALBERS_M(cos_lat2, one_minus_sqr_e_sin2);
		q2 = ALBERS_Q(sin_lat2, one_minus_sqr_e_sin2, e_sin2);
		sqr_m2 = m2 * m2;
		_n = (sqr_m1 - sqr_m2) / (q2 - q1);
	} else
		_n = sin_lat1;

	_c = sqr_m1 + _n * q1;
	_a_over_n = ellipsoid.radius() / _n;
	nq0 = _n * q0;
	_rho0 = (_c < nq0) ? 0 : _a_over_n * sqrt(_c - nq0);
}

PointD AlbersEqual::ll2xy(const Coordinates &c) const
{
	double dlam;
	double sin_lat;
	double e_sin;
	double q;
	double rho;
	double theta;
	double nq;


	dlam = deg2rad(c.lon()) - _longitudeOrigin;
	if (dlam > M_PI)
		dlam -= 2 * M_PI;
	if (dlam < -M_PI)
		dlam += 2 * M_PI;

	sin_lat = sin(deg2rad(c.lat()));
	e_sin = _e * sin_lat;
	q = ALBERS_Q(sin_lat, ONE_MINUS_SQR(e_sin), e_sin);
	nq = _n * q;
	rho = (_c < nq) ? 0 : _a_over_n * sqrt(_c - nq);
	theta = _n * dlam;

	return PointD(rho * sin(theta) + _falseEasting,
	  _rho0 - rho * cos(theta) + _falseNorthing);
}

Coordinates AlbersEqual::xy2ll(const PointD &p) const
{
	double dy, dx;
	double rho0_minus_dy;
	double q, qc, q_over_2;
	double rho, rho_n;
	double phi, delta_phi = 1.0;
	double sin_phi;
	double e_sin, one_minus_sqr_e_sin;
	double theta = 0.0;
	int count = 30;
	double tolerance = 4.85e-10;
	double lat, lon;


	dy = p.y() - _falseNorthing;
	dx = p.x() - _falseEasting;

	rho0_minus_dy = _rho0 - dy;
	rho = sqrt(dx * dx + rho0_minus_dy * rho0_minus_dy);

	if (_n < 0) {
		rho *= -1.0;
		dx *= -1.0;
		rho0_minus_dy *= -1.0;
	}

	if (rho != 0.0)
		theta = atan2(dx, rho0_minus_dy);
	rho_n = rho * _n;
	q = (_c - (rho_n * rho_n) / _a2) / _n;
	qc = 1 - ((_one_minus_es) / (_two_e)) * log((1.0 - _e) / (1.0 + _e));
	if (fabs(fabs(qc) - fabs(q)) > 1.0e-6) {
		q_over_2 = q / 2.0;
		if (q_over_2 > 1.0)
			lat = M_PI_2;
		else if (q_over_2 < -1.0)
			lat = -M_PI_2;
		else {
			phi = asin(q_over_2);
			if (_e < 1.0e-10)
				lat = phi;
			else  {
				while ((fabs(delta_phi) > tolerance) && count) {
					sin_phi = sin(phi);
					e_sin = _e * sin_phi;
					one_minus_sqr_e_sin = ONE_MINUS_SQR(e_sin);
					delta_phi = (one_minus_sqr_e_sin * one_minus_sqr_e_sin)
					  / (2.0 * cos(phi)) * (q / (_one_minus_es) - sin_phi
					  / one_minus_sqr_e_sin + (log((1.0 - e_sin)
					  / (1.0 + e_sin)) / (_two_e)));
					phi += delta_phi;
					count --;
				}

				lat = phi;
			}

			if (lat > M_PI_2)
				lat = M_PI_2;
			else if (lat < -M_PI_2)
				lat = -M_PI_2;
		}
	} else {
		if (q >= 0.0)
			lat = M_PI_2;
		else
			lat = -M_PI_2;
	}

	lon = _longitudeOrigin + theta / _n;

	if (lon > M_PI)
		lon -= 2 * M_PI;
	if (lon < -M_PI)
		lon += 2 * M_PI;

	if (lon > M_PI)
		lon = M_PI;
	else if (lon < -M_PI)
		lon = -M_PI;

	return Coordinates(rad2deg(lon), rad2deg(lat));
}

bool AlbersEqual::operator==(const CT &ct) const
{
	const AlbersEqual *other = dynamic_cast<const AlbersEqual*>(&ct);
	return (other != 0 && _latitudeOrigin == other->_latitudeOrigin
	  && _longitudeOrigin == other->_longitudeOrigin
	  && _falseEasting == other->_falseEasting
	  && _falseNorthing == other->_falseNorthing && _a2 == other->_a2
	  && _es == other->_es && _rho0 == other->_rho0 && _c == other->_c
	  && _n == other->_n);
}