1 /**************************************************************************
3 * Written by Durk Talsma. Originally started October 1997, for distribution
4 * with the FlightGear project. Version 2 was written in August and
5 * September 1998. This code is based upon algorithms and data kindly
6 * provided by Mr. Paul Schlyter. (pausch@saaf.se).
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Library General Public
10 * License as published by the Free Software Foundation; either
11 * version 2 of the License, or (at your option) any later version.
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Library General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
23 **************************************************************************/
28 #include <simgear/debug/logstream.hxx>
31 # define exception c_exception
35 // #include <FDM/flight.hxx>
37 #include "moonpos.hxx"
40 /*************************************************************************
41 * MoonPos::MoonPos(double mjd)
42 * Public constructor for class MoonPos. Initializes the orbital elements and
43 * sets up the moon texture.
44 * Argument: The current time.
45 * the hard coded orbital elements for MoonPos are passed to
46 * CelestialBody::CelestialBody();
47 ************************************************************************/
48 MoonPos::MoonPos(double mjd) :
49 CelestialBody(125.1228, -0.0529538083,
51 318.0634, 0.1643573223,
54 115.3654, 13.0649929509, mjd)
59 CelestialBody(125.1228, -0.0529538083,
61 318.0634, 0.1643573223,
64 115.3654, 13.0649929509)
74 /*****************************************************************************
75 * void MoonPos::updatePosition(double mjd, Star *ourSun)
76 * this member function calculates the actual topocentric position (i.e.)
77 * the position of the moon as seen from the current position on the surface
79 ****************************************************************************/
80 void MoonPos::updatePosition(double mjd, double lst, double lat, Star *ourSun)
83 eccAnom, ecl, actTime,
84 xv, yv, v, r, xh, yh, zh, xg, yg, zg, xe, ye, ze,
85 Ls, Lm, D, F, mpar, gclat, rho, HA, g,
88 updateOrbElements(mjd);
89 actTime = sgCalcActTime(mjd);
91 // calculate the angle between ecliptic and equatorial coordinate system
93 ecl = ((SGD_DEGREES_TO_RADIANS * 23.4393) - (SGD_DEGREES_TO_RADIANS * 3.563E-7) * actTime);
94 eccAnom = sgCalcEccAnom(M, e); // Calculate the eccentric anomaly
95 xv = a * (cos(eccAnom) - e);
96 yv = a * (sqrt(1.0 - e*e) * sin(eccAnom));
97 v = atan2(yv, xv); // the moon's true anomaly
98 r = sqrt (xv*xv + yv*yv); // and its distance
100 // estimate the geocentric rectangular coordinates here
101 xh = r * (cos(N) * cos (v+w) - sin (N) * sin(v+w) * cos(i));
102 yh = r * (sin(N) * cos (v+w) + cos (N) * sin(v+w) * cos(i));
103 zh = r * (sin(v+w) * sin(i));
105 // calculate the ecliptic latitude and longitude here
106 lonEcl = atan2 (yh, xh);
107 latEcl = atan2(zh, sqrt(xh*xh + yh*yh));
109 /* Calculate a number of perturbatioin, i.e. disturbances caused by the
110 * gravitational infuence of the sun and the other major planets.
111 * The largest of these even have a name */
112 Ls = ourSun->getM() + ourSun->getw();
117 lonEcl += SGD_DEGREES_TO_RADIANS * (-1.274 * sin (M - 2*D)
119 -0.186 * sin(ourSun->getM())
120 -0.059 * sin(2*M - 2*D)
121 -0.057 * sin(M - 2*D + ourSun->getM())
122 +0.053 * sin(M + 2*D)
123 +0.046 * sin(2*D - ourSun->getM())
124 +0.041 * sin(M - ourSun->getM())
126 -0.031 * sin(M + ourSun->getM())
127 -0.015 * sin(2*F - 2*D)
128 +0.011 * sin(M - 4*D)
130 latEcl += SGD_DEGREES_TO_RADIANS * (-0.173 * sin(F-2*D)
131 -0.055 * sin(M - F - 2*D)
132 -0.046 * sin(M + F - 2*D)
133 +0.033 * sin(F + 2*D)
134 +0.017 * sin(2*M + F)
136 r += (-0.58 * cos(M - 2*D)
139 // SG_LOG(SG_GENERAL, SG_INFO, "Running moon update");
140 xg = r * cos(lonEcl) * cos(latEcl);
141 yg = r * sin(lonEcl) * cos(latEcl);
142 zg = r * sin(latEcl);
145 ye = yg * cos(ecl) -zg * sin(ecl);
146 ze = yg * sin(ecl) +zg * cos(ecl);
148 geoRa = atan2(ye, xe);
149 geoDec = atan2(ze, sqrt(xe*xe + ye*ye));
151 /* SG_LOG( SG_GENERAL, SG_INFO,
152 "(geocentric) geoRa = (" << (SGD_RADIANS_TO_DEGREES * geoRa)
153 << "), geoDec= (" << (SGD_RADIANS_TO_DEGREES * geoDec) << ")" ); */
156 // Given the moon's geocentric ra and dec, calculate its
157 // topocentric ra and dec. i.e. the position as seen from the
158 // surface of the earth, instead of the center of the earth
160 // First calculate the moon's parrallax, that is, the apparent size of the
161 // (equatorial) radius of the earth, as seen from the moon
162 mpar = asin ( 1 / r);
163 // SG_LOG( SG_GENERAL, SG_INFO, "r = " << r << " mpar = " << mpar );
164 // SG_LOG( SG_GENERAL, SG_INFO, "lat = " << f->get_Latitude() );
166 gclat = lat - 0.003358 *
167 sin (2 * SGD_DEGREES_TO_RADIANS * lat );
168 // SG_LOG( SG_GENERAL, SG_INFO, "gclat = " << gclat );
170 rho = 0.99883 + 0.00167 * cos(2 * SGD_DEGREES_TO_RADIANS * lat);
171 // SG_LOG( SG_GENERAL, SG_INFO, "rho = " << rho );
176 HA = lst - (3.8197186 * geoRa);
177 /* SG_LOG( SG_GENERAL, SG_INFO, "t->getLst() = " << t->getLst()
178 << " HA = " << HA ); */
180 g = atan (tan(gclat) / cos ((HA / 3.8197186)));
181 // SG_LOG( SG_GENERAL, SG_INFO, "g = " << g );
183 rightAscension = geoRa - mpar * rho * cos(gclat) * sin(HA) / cos (geoDec);
186 = geoDec - mpar * rho * sin (gclat) * sin (g - geoDec) / sin(g);
188 declination = geoDec;
189 // cerr << "Geocentric vs. Topocentric position" << endl;
190 // cerr << "RA (difference) : "
191 // << SGD_RADIANS_TO_DEGREES * (geoRa - rightAscension) << endl;
192 // cerr << "Dec (difference) : "
193 // << SGD_RADIANS_TO_DEGREES * (geoDec - declination) << endl;
196 /* SG_LOG( SG_GENERAL, SG_INFO,
197 "Ra = (" << (SGD_RADIANS_TO_DEGREES *rightAscension)
198 << "), Dec= (" << (SGD_RADIANS_TO_DEGREES *declination) << ")" ); */