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 program is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU General Public License as
10 * published by the Free Software Foundation; either version 2 of the
11 * License, or (at your option) any later version.
13 * This program is distributed in the hope that it will be useful, but
14 * WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * 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., 675 Mass Ave, Cambridge, MA 02139, USA.
23 **************************************************************************/
28 #include <simgear/debug/logstream.hxx>
29 #include <simgear/misc/fgpath.hxx>
31 #include <Main/options.hxx>
32 #include <Objects/texload.h>
35 # define exception c_exception
39 #include <FDM/flight.hxx>
44 /*************************************************************************
45 * Moon::Moon(FGTime *t)
46 * Public constructor for class Moon. Initializes the orbital elements and
47 * sets up the moon texture.
48 * Argument: The current time.
49 * the hard coded orbital elements for Moon are passed to
50 * CelestialBody::CelestialBody();
51 ************************************************************************/
52 Moon::Moon(FGTime *t) :
53 CelestialBody(125.1228, -0.0529538083,
55 318.0634, 0.1643573223,
58 115.3654, 13.0649929509, t)
63 CelestialBody(125.1228, -0.0529538083,
65 318.0634, 0.1643573223,
68 115.3654, 13.0649929509)
78 /*****************************************************************************
79 * void Moon::updatePosition(FGTime *t, Star *ourSun)
80 * this member function calculates the actual topocentric position (i.e.)
81 * the position of the moon as seen from the current position on the surface
83 ****************************************************************************/
84 void Moon::updatePosition(FGTime *t, double lat, Star *ourSun)
87 eccAnom, ecl, actTime,
88 xv, yv, v, r, xh, yh, zh, xg, yg, zg, xe, ye, ze,
89 Ls, Lm, D, F, mpar, gclat, rho, HA, g,
95 air = ¤t_aircraft;
99 actTime = fgCalcActTime(t);
101 // calculate the angle between ecliptic and equatorial coordinate system
103 ecl = ((DEG_TO_RAD * 23.4393) - (DEG_TO_RAD * 3.563E-7) * actTime);
104 eccAnom = fgCalcEccAnom(M, e); // Calculate the eccentric anomaly
105 xv = a * (cos(eccAnom) - e);
106 yv = a * (sqrt(1.0 - e*e) * sin(eccAnom));
107 v = atan2(yv, xv); // the moon's true anomaly
108 r = sqrt (xv*xv + yv*yv); // and its distance
110 // estimate the geocentric rectangular coordinates here
111 xh = r * (cos(N) * cos (v+w) - sin (N) * sin(v+w) * cos(i));
112 yh = r * (sin(N) * cos (v+w) + cos (N) * sin(v+w) * cos(i));
113 zh = r * (sin(v+w) * sin(i));
115 // calculate the ecliptic latitude and longitude here
116 lonEcl = atan2 (yh, xh);
117 latEcl = atan2(zh, sqrt(xh*xh + yh*yh));
119 /* Calculate a number of perturbatioin, i.e. disturbances caused by the
120 * gravitational infuence of the sun and the other major planets.
121 * The largest of these even have a name */
122 Ls = ourSun->getM() + ourSun->getw();
127 lonEcl += DEG_TO_RAD * (-1.274 * sin (M - 2*D)
129 -0.186 * sin(ourSun->getM())
130 -0.059 * sin(2*M - 2*D)
131 -0.057 * sin(M - 2*D + ourSun->getM())
132 +0.053 * sin(M + 2*D)
133 +0.046 * sin(2*D - ourSun->getM())
134 +0.041 * sin(M - ourSun->getM())
136 -0.031 * sin(M + ourSun->getM())
137 -0.015 * sin(2*F - 2*D)
138 +0.011 * sin(M - 4*D)
140 latEcl += DEG_TO_RAD * (-0.173 * sin(F-2*D)
141 -0.055 * sin(M - F - 2*D)
142 -0.046 * sin(M + F - 2*D)
143 +0.033 * sin(F + 2*D)
144 +0.017 * sin(2*M + F)
146 r += (-0.58 * cos(M - 2*D)
149 // FG_LOG(FG_GENERAL, FG_INFO, "Running moon update");
150 xg = r * cos(lonEcl) * cos(latEcl);
151 yg = r * sin(lonEcl) * cos(latEcl);
152 zg = r * sin(latEcl);
155 ye = yg * cos(ecl) -zg * sin(ecl);
156 ze = yg * sin(ecl) +zg * cos(ecl);
158 geoRa = atan2(ye, xe);
159 geoDec = atan2(ze, sqrt(xe*xe + ye*ye));
161 /* FG_LOG( FG_GENERAL, FG_INFO,
162 "(geocentric) geoRa = (" << (RAD_TO_DEG * geoRa)
163 << "), geoDec= (" << (RAD_TO_DEG * geoDec) << ")" ); */
166 // Given the moon's geocentric ra and dec, calculate its
167 // topocentric ra and dec. i.e. the position as seen from the
168 // surface of the earth, instead of the center of the earth
170 // First calculate the moon's parrallax, that is, the apparent size of the
171 // (equatorial) radius of the earth, as seen from the moon
172 mpar = asin ( 1 / r);
173 // FG_LOG( FG_GENERAL, FG_INFO, "r = " << r << " mpar = " << mpar );
174 // FG_LOG( FG_GENERAL, FG_INFO, "lat = " << f->get_Latitude() );
176 gclat = lat - 0.003358 *
177 sin (2 * DEG_TO_RAD * lat );
178 // FG_LOG( FG_GENERAL, FG_INFO, "gclat = " << gclat );
180 rho = 0.99883 + 0.00167 * cos(2 * DEG_TO_RAD * lat);
181 // FG_LOG( FG_GENERAL, FG_INFO, "rho = " << rho );
186 HA = t->getLst() - (3.8197186 * geoRa);
187 /* FG_LOG( FG_GENERAL, FG_INFO, "t->getLst() = " << t->getLst()
188 << " HA = " << HA ); */
190 g = atan (tan(gclat) / cos ((HA / 3.8197186)));
191 // FG_LOG( FG_GENERAL, FG_INFO, "g = " << g );
193 rightAscension = geoRa - mpar * rho * cos(gclat) * sin(HA) / cos (geoDec);
194 declination = geoDec - mpar * rho * sin (gclat) * sin (g - geoDec) / sin(g);
196 /* FG_LOG( FG_GENERAL, FG_INFO,
197 "Ra = (" << (RAD_TO_DEG *rightAscension)
198 << "), Dec= (" << (RAD_TO_DEG *declination) << ")" ); */