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simgear/simgear/ephemeris/moonpos.cxx
Scott Giese 469a28c49a Remove obsolete, unused variable
2021-02-13 21:44:25 -06:00

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/**************************************************************************
* moonpos.cxx
* Written by Durk Talsma. Originally started October 1997, for distribution
* with the FlightGear project. Version 2 was written in August and
* September 1998. This code is based upon algorithms and data kindly
* provided by Mr. Paul Schlyter. (pausch@saaf.se).
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Library General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Library General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*
* $Id$
**************************************************************************/
#include <simgear_config.h>
#include <string.h>
#include <simgear/debug/logstream.hxx>
#include <simgear/math/SGMath.hxx>
#include <math.h>
// #include <FDM/flight.hxx>
#include "moonpos.hxx"
/*************************************************************************
* MoonPos::MoonPos(double mjd)
* Public constructor for class MoonPos. Initializes the orbital elements and
* sets up the moon texture.
* Argument: The current time.
* the hard coded orbital elements for MoonPos are passed to
* CelestialBody::CelestialBody();
************************************************************************/
MoonPos::MoonPos(double mjd) :
CelestialBody(125.1228, -0.0529538083,
5.1454, 0.00000,
318.0634, 0.1643573223,
60.266600, 0.000000,
0.054900, 0.000000,
115.3654, 13.0649929509, mjd)
{
}
MoonPos::MoonPos() :
CelestialBody(125.1228, -0.0529538083,
5.1454, 0.00000,
318.0634, 0.1643573223,
60.266600, 0.000000,
0.054900, 0.000000,
115.3654, 13.0649929509)
{
}
MoonPos::~MoonPos()
{
}
/*****************************************************************************
* void MoonPos::updatePositionTopo(double mjd, double lst, double
* lat, Star *ourSun) this member function calculates the actual
* topocentric position (i.e.) the position of the moon as seen from
* the current position on the surface of the earth. This include
* parallax effects, the moon appears on different stars background
* for different observers on the surface of the earth.
****************************************************************************/
void MoonPos::updatePositionTopo(double mjd, double lst, double lat, Star *ourSun)
{
double
eccAnom, ecl, actTime,
xv, yv, v, r, xh, yh, zh, zg, xe,
Ls, Lm, D, F, mpar, gclat, rho, HA, g,
geoRa, geoDec,
cosN, sinN, cosvw, sinvw, sinvw_cosi, cosecl, sinecl, rcoslatEcl,
FlesstwoD, MlesstwoD, twoD, twoM, twolat, alpha;
double max_loglux = -0.504030345621;
double min_loglux = -4.39964634562;
double conv = 1.0319696543787917; // The log foot-candle to log lux conversion factor.
updateOrbElements(mjd);
actTime = sgCalcActTime(mjd);
// calculate the angle between ecliptic and equatorial coordinate system
// in Radians
ecl = SGD_DEGREES_TO_RADIANS * (23.4393 - 3.563E-7 * actTime);
eccAnom = sgCalcEccAnom(M, e); // Calculate the eccentric anomaly
xv = a * (cos(eccAnom) - e);
yv = a * (sqrt(1.0 - e*e) * sin(eccAnom));
v = atan2(yv, xv); // the moon's true anomaly
r = sqrt (xv*xv + yv*yv); // and its distance
// repetitive calculations, minimised for speed
cosN = cos(N);
sinN = sin(N);
cosvw = cos(v+w);
sinvw = sin(v+w);
sinvw_cosi = sinvw * cos(i);
cosecl = cos(ecl);
sinecl = sin(ecl);
// estimate the geocentric rectangular coordinates here
xh = r * (cosN * cosvw - sinN * sinvw_cosi);
yh = r * (sinN * cosvw + cosN * sinvw_cosi);
zh = r * (sinvw * sin(i));
// calculate the ecliptic latitude and longitude here
lonEcl = atan2 (yh, xh);
latEcl = atan2(zh, sqrt(xh*xh + yh*yh));
/* Calculate a number of perturbation, i.e. disturbances caused by the
* gravitational influence of the sun and the other major planets.
* The largest of these even have a name */
Ls = ourSun->getM() + ourSun->getw();
Lm = M + w + N;
D = Lm - Ls;
F = Lm - N;
twoD = 2 * D;
twoM = 2 * M;
FlesstwoD = F - twoD;
MlesstwoD = M - twoD;
lonEcl += SGD_DEGREES_TO_RADIANS * (-1.274 * sin(MlesstwoD)
+0.658 * sin(twoD)
-0.186 * sin(ourSun->getM())
-0.059 * sin(twoM - twoD)
-0.057 * sin(MlesstwoD + ourSun->getM())
+0.053 * sin(M + twoD)
+0.046 * sin(twoD - ourSun->getM())
+0.041 * sin(M - ourSun->getM())
-0.035 * sin(D)
-0.031 * sin(M + ourSun->getM())
-0.015 * sin(2*F - twoD)
+0.011 * sin(M - 4*D)
);
latEcl += SGD_DEGREES_TO_RADIANS * (-0.173 * sin(FlesstwoD)
-0.055 * sin(M - FlesstwoD)
-0.046 * sin(M + FlesstwoD)
+0.033 * sin(F + twoD)
+0.017 * sin(twoM + F)
);
r += (-0.58 * cos(MlesstwoD)
-0.46 * cos(twoD)
);
distance = r;
distance_in_a = r/a;
// SG_LOG(SG_GENERAL, SG_INFO, "Running moon update");
rcoslatEcl = r * cos(latEcl);
xg = cos(lonEcl) * rcoslatEcl;
yg = sin(lonEcl) * rcoslatEcl;
zg = r * sin(latEcl);
xe = xg;
ye = yg * cosecl -zg * sinecl;
ze = yg * sinecl +zg * cosecl;
geoRa = atan2(ye, xe);
geoDec = atan2(ze, sqrt(xe*xe + ye*ye));
/* SG_LOG( SG_GENERAL, SG_INFO,
"(geocentric) geoRa = (" << (SGD_RADIANS_TO_DEGREES * geoRa)
<< "), geoDec= (" << (SGD_RADIANS_TO_DEGREES * geoDec) << ")" ); */
// Given the moon's geocentric ra and dec, calculate its
// topocentric ra and dec. i.e. the position as seen from the
// surface of the earth, instead of the center of the earth
// First calculate the moon's parallax, that is, the apparent size of the
// (equatorial) radius of the earth, as seen from the moon
mpar = asin ( 1 / r);
// SG_LOG( SG_GENERAL, SG_INFO, "r = " << r << " mpar = " << mpar );
// SG_LOG( SG_GENERAL, SG_INFO, "lat = " << f->get_Latitude() );
twolat = 2 * SGD_DEGREES_TO_RADIANS * lat;
gclat = lat - 0.003358 * sin(twolat);
// SG_LOG( SG_GENERAL, SG_INFO, "gclat = " << gclat );
rho = 0.99883 + 0.00167 * cos(twolat);
// SG_LOG( SG_GENERAL, SG_INFO, "rho = " << rho );
if (geoRa < 0)
geoRa += SGD_2PI;
HA = lst - (3.8197186 * geoRa);
/* SG_LOG( SG_GENERAL, SG_INFO, "t->getLst() = " << t->getLst()
<< " HA = " << HA ); */
g = atan (tan(gclat) / cos ((HA / 3.8197186)));
// SG_LOG( SG_GENERAL, SG_INFO, "g = " << g );
rightAscension = geoRa - mpar * rho * cos(gclat) * sin(HA) / cos (geoDec);
if (fabs(lat) > 0) {
declination
= geoDec - mpar * rho * sin (gclat) * sin (g - geoDec) / sin(g);
} else {
declination = geoDec;
// cerr << "Geocentric vs. Topocentric position" << endl;
// cerr << "RA (difference) : "
// << SGD_RADIANS_TO_DEGREES * (geoRa - rightAscension) << endl;
// cerr << "Dec (difference) : "
// << SGD_RADIANS_TO_DEGREES * (geoDec - declination) << endl;
}
/* SG_LOG( SG_GENERAL, SG_INFO,
"Ra = (" << (SGD_RADIANS_TO_DEGREES *rightAscension)
<< "), Dec= (" << (SGD_RADIANS_TO_DEGREES *declination) << ")" ); */
// Moon age and phase calculation
age = lonEcl - ourSun->getlonEcl();
phase = (1 - cos(age)) / 2;
// The log of the illuminance of the moon outside the atmosphere.
// This is the base 10 log of equation 20 from Krisciunas K. and Schaefer B.E.
// (1991). A model of the brightness of moonlight, Publ. Astron. Soc. Pacif.
// 103(667), 1033-1039 (DOI: http://dx.doi.org/10.1086/132921).
alpha = SGD_RADIANS_TO_DEGREES * SGMiscd::normalizeAngle(age + SGMiscd::pi());
log_I = -0.4 * (3.84 + 0.026*fabs(alpha) + 4e-9*pow(alpha, 4.0));
// Convert from foot-candles to lux.
log_I += conv;
// The moon's illuminance factor, bracketed between 0 and 1.
I_factor = (log_I - max_loglux) / (max_loglux - min_loglux) + 1.0;
I_factor = SGMiscd::clip(I_factor, 0, 1);
}
/*****************************************************************************
* void MoonPos::updatePosition(double mjd, Star *ourSun) this member
* function calculates the geocentric position (i.e.) the position of
* the moon as seen from the center of earth. As such, it does not
* include any parallax effects. These are taken into account during
* the rendering.
****************************************************************************/
void MoonPos::updatePosition(double mjd, Star *ourSun)
{
double
eccAnom, ecl, actTime,
xv, yv, v, r, xh, yh, zh, zg, xe,
Ls, Lm, D, F, geoRa, geoDec,
cosN, sinN, cosvw, sinvw, sinvw_cosi, cosecl, sinecl, rcoslatEcl,
FlesstwoD, MlesstwoD, twoD, twoM, alpha;
double max_loglux = -0.504030345621;
double min_loglux = -4.39964634562;
double conv = 1.0319696543787917; // The log foot-candle to log lux conversion factor.
updateOrbElements(mjd);
actTime = sgCalcActTime(mjd);
// calculate the angle between ecliptic and equatorial coordinate system
// in Radians
ecl = SGD_DEGREES_TO_RADIANS * (23.4393 - 3.563E-7 * actTime);
eccAnom = sgCalcEccAnom(M, e); // Calculate the eccentric anomaly
xv = a * (cos(eccAnom) - e);
yv = a * (sqrt(1.0 - e*e) * sin(eccAnom));
v = atan2(yv, xv); // the moon's true anomaly
r = sqrt (xv*xv + yv*yv); // and its distance
// repetitive calculations, minimised for speed
cosN = cos(N);
sinN = sin(N);
cosvw = cos(v+w);
sinvw = sin(v+w);
sinvw_cosi = sinvw * cos(i);
cosecl = cos(ecl);
sinecl = sin(ecl);
// estimate the geocentric rectangular coordinates here
xh = r * (cosN * cosvw - sinN * sinvw_cosi);
yh = r * (sinN * cosvw + cosN * sinvw_cosi);
zh = r * (sinvw * sin(i));
// calculate the ecliptic latitude and longitude here
lonEcl = atan2 (yh, xh);
latEcl = atan2(zh, sqrt(xh*xh + yh*yh));
/* Calculate a number of perturbation, i.e. disturbances caused by the
* gravitational influence of the sun and the other major planets.
* The largest of these even have a name */
Ls = ourSun->getM() + ourSun->getw();
Lm = M + w + N;
D = Lm - Ls;
F = Lm - N;
twoD = 2 * D;
twoM = 2 * M;
FlesstwoD = F - twoD;
MlesstwoD = M - twoD;
lonEcl += SGD_DEGREES_TO_RADIANS * (-1.274 * sin(MlesstwoD)
+0.658 * sin(twoD)
-0.186 * sin(ourSun->getM())
-0.059 * sin(twoM - twoD)
-0.057 * sin(MlesstwoD + ourSun->getM())
+0.053 * sin(M + twoD)
+0.046 * sin(twoD - ourSun->getM())
+0.041 * sin(M - ourSun->getM())
-0.035 * sin(D)
-0.031 * sin(M + ourSun->getM())
-0.015 * sin(2*F - twoD)
+0.011 * sin(M - 4*D)
);
latEcl += SGD_DEGREES_TO_RADIANS * (-0.173 * sin(FlesstwoD)
-0.055 * sin(M - FlesstwoD)
-0.046 * sin(M + FlesstwoD)
+0.033 * sin(F + twoD)
+0.017 * sin(twoM + F)
);
r += (-0.58 * cos(MlesstwoD)
-0.46 * cos(twoD)
);
// from the orbital elements, the unit of the distance is in Earth radius, around 60.
distance = r;
distance_in_a = r/a;
// SG_LOG(SG_GENERAL, SG_INFO, "Running moon update");
rcoslatEcl = r * cos(latEcl);
xg = cos(lonEcl) * rcoslatEcl;
yg = sin(lonEcl) * rcoslatEcl;
zg = r * sin(latEcl);
xe = xg;
ye = yg * cosecl -zg * sinecl;
ze = yg * sinecl +zg * cosecl;
geoRa = atan2(ye, xe);
geoDec = atan2(ze, sqrt(xe*xe + ye*ye));
if (geoRa < 0)
geoRa += SGD_2PI;
rightAscension = geoRa;
declination = geoDec;
/* SG_LOG( SG_GENERAL, SG_INFO,
"Ra = (" << (SGD_RADIANS_TO_DEGREES *rightAscension)
<< "), Dec= (" << (SGD_RADIANS_TO_DEGREES *declination) << ")" ); */
// Moon age and phase calculation
age = lonEcl - ourSun->getlonEcl();
phase = (1 - cos(age)) / 2;
// The log of the illuminance of the moon outside the atmosphere.
// This is the base 10 log of equation 20 from Krisciunas K. and Schaefer B.E.
// (1991). A model of the brightness of moonlight, Publ. Astron. Soc. Pacif.
// 103(667), 1033-1039 (DOI: http://dx.doi.org/10.1086/132921).
alpha = SGD_RADIANS_TO_DEGREES * SGMiscd::normalizeAngle(age + SGMiscd::pi());
log_I = -0.4 * (3.84 + 0.026*fabs(alpha) + 4e-9*pow(alpha, 4.0));
// Convert from foot-candles to lux.
log_I += conv;
// The moon's illuminance factor, bracketed between 0 and 1.
I_factor = (log_I - max_loglux) / (max_loglux - min_loglux) + 1.0;
I_factor = SGMiscd::clip(I_factor, 0, 1);
}
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