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flightgear/Astro/moon.c
curt e798c59696 Incorporated Durk's Astro/ tweaks. Includes unifying the sun position 
calculation code between sun display, and other FG sections that use this
for things like lighting.
1998-02-23 19:07:49 +00:00

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/**************************************************************************
* moon.c
* Written by Durk Talsma. Started October 1997, for the flight gear project.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program 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
* 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., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* $Id$
* (Log is kept at end of this file)
**************************************************************************/
#include <math.h>
#include <GL/glut.h>
#include <XGL/xgl.h>
#include <Astro/orbits.h>
#include <Astro/moon.h>
#include <Aircraft/aircraft.h>
#include <Include/fg_constants.h>
#include <Include/general.h>
#include <Main/views.h>
#include <Time/fg_time.h>
#include <Main/fg_debug.h>
struct CelestialCoord moonPos;
static float xMoon, yMoon, zMoon;
static GLint moon = 0;
/* --------------------------------------------------------------
This section contains the code that calculates the actual
position of the moon in the night sky.
----------------------------------------------------------------*/
struct CelestialCoord fgCalculateMoon(struct OrbElements params,
struct OrbElements sunParams,
struct fgTIME t)
{
struct CelestialCoord
geocCoord, topocCoord;
double
eccAnom, ecl, lonecl, latecl, actTime,
xv, yv, v, r, xh, yh, zh, xg, yg, zg, xe, ye, ze,
Ls, Lm, D, F, mpar, gclat, rho, HA, g;
fgAIRCRAFT *a;
fgFLIGHT *f;
a = &current_aircraft;
f = a->flight;
/* calculate the angle between ecliptic and equatorial coordinate
* system, in Radians */
actTime = fgCalcActTime(t);
ecl = ((DEG_TO_RAD * 23.4393) - (DEG_TO_RAD * 3.563E-7) * actTime);
/*ecl = 0.409093 - 6.2186E-9 * actTime; */
/* calculate the eccentric anomaly */
eccAnom = fgCalcEccAnom(params.M, params.e);
/* calculate the moon's distance (r) and true anomaly (v) */
xv = params.a * ( cos(eccAnom) - params.e);
yv = params.a * ( sqrt(1.0 - params.e*params.e) * sin(eccAnom));
v =atan2(yv, xv);
r = sqrt(xv*xv + yv*yv);
/* estimate the geocentric rectangular coordinates here */
xh = r * (cos (params.N) * cos (v + params.w) -
sin (params.N) * sin (v + params.w) * cos (params.i));
yh = r * (sin (params.N) * cos (v + params.w) +
cos (params.N) * sin (v + params.w) * cos (params.i));
zh = r * (sin(v + params.w) * sin(params.i));
/* calculate the ecliptic latitude and longitude here */
lonecl = atan2( yh, xh);
latecl = atan2( zh, sqrt( xh*xh + yh*yh));
/* calculate a number of perturbations, i.e. disturbances caused by
* the gravitational influence of the sun and the other mayor
* planets. The largest of these even have their own names */
Ls = sunParams.M + sunParams.w;
Lm = params.M + params.w + params.N;
D = Lm - Ls;
F = Lm - params.N;
lonecl += DEG_TO_RAD * (
- 1.274 * sin (params.M - 2*D) /* the Evection */
+ 0.658 * sin (2 * D) /* the Variation */
- 0.186 * sin (sunParams.M) /* the yearly variation */
- 0.059 * sin (2*params.M - 2*D)
- 0.057 * sin (params.M - 2*D + sunParams.M)
+ 0.053 * sin (params.M + 2*D)
+ 0.046 * sin (2*D - sunParams.M)
+ 0.041 * sin (params.M - sunParams.M)
- 0.035 * sin (D) /* the Parallactic Equation */
- 0.031 * sin (params.M + sunParams.M)
- 0.015 * sin (2*F - 2*D)
+ 0.011 * sin (params.M - 4*D)
);
latecl += DEG_TO_RAD * (
- 0.173 * sin (F - 2*D)
- 0.055 * sin (params.M - F - 2*D)
- 0.046 * sin (params.M + F - 2*D)
+ 0.033 * sin (F + 2*D)
+ 0.017 * sin (2 * params.M + F)
);
r += (
- 0.58 * cos(params.M - 2*D)
- 0.46 * cos(2*D)
);
xg = r * cos(lonecl) * cos(latecl);
yg = r * sin(lonecl) * cos(latecl);
zg = r * sin(latecl);
xe = xg;
ye = yg * cos(ecl) - zg * sin(ecl);
ze = yg * sin(ecl) + zg * cos(ecl);
geocCoord.RightAscension = atan2(ye, xe);
geocCoord.Declination = atan2(ze, sqrt(xe*xe + ye*ye));
/* New since 25 december 1997 */
/* Calculate the moon's topocentric position instead of it's geocentric! */
/* calculate the moon's parrallax, i.e. the apparent size of the
* (equatorial) radius of the Earth, as seen from the moon */
mpar = asin( 1 / r);
gclat = FG_Latitude - 0.083358 * sin (2 * DEG_TO_RAD * FG_Latitude);
rho = 0.99883 + 0.00167 * cos(2 * DEG_TO_RAD * FG_Latitude);
if (geocCoord.RightAscension < 0)
geocCoord.RightAscension += (2*FG_PI);
HA = t.lst - (3.8197186 * geocCoord.RightAscension);
g = atan (tan(gclat) / cos( (HA / 3.8197186)));
topocCoord.RightAscension = geocCoord.RightAscension -
mpar * rho * cos (gclat) * sin (HA) / cos (geocCoord.Declination);
topocCoord.Declination = geocCoord.Declination -
mpar * rho * sin (gclat) * sin (g - geocCoord.Declination) / sin (g);
return topocCoord;
}
void fgMoonInit( void ) {
GLfloat moonColor[4] = {0.85, 0.75, 0.35, 1.0};
GLfloat black[4] = { 0.0, 0.0, 0.0, 1.0 };
fgPrintf( FG_ASTRO, FG_INFO, "Initializing the Moon\n");
fgSolarSystemUpdate(&(pltOrbElements[1]), cur_time_params);
moonPos = fgCalculateMoon(pltOrbElements[1], pltOrbElements[0],
cur_time_params);
fgPrintf( FG_ASTRO, FG_DEBUG,
"Moon found at %f (ra), %f (dec)\n", moonPos.RightAscension,
moonPos.Declination);
xMoon = 60000.0 * cos(moonPos.RightAscension) * cos(moonPos.Declination);
yMoon = 60000.0 * sin(moonPos.RightAscension) * cos(moonPos.Declination);
zMoon = 60000.0 * sin(moonPos.Declination);
if (moon) {
xglDeleteLists (moon, 1);
}
moon = xglGenLists (1);
xglNewList (moon, GL_COMPILE);
xglMaterialfv (GL_FRONT, GL_AMBIENT, black);
xglMaterialfv (GL_FRONT, GL_DIFFUSE, moonColor);
xglPushMatrix ();
xglTranslatef (xMoon, yMoon, zMoon);
xglScalef (1400, 1400, 1400);
glutSolidSphere (1.0, 10, 10);
xglPopMatrix ();
xglEndList ();
}
/* Draw the moon */
void fgMoonRender( void ) {
xglCallList(moon);
}
/* $Log$
/* Revision 1.7 1998/02/23 19:07:54 curt
/* Incorporated Durk's Astro/ tweaks. Includes unifying the sun position
/* calculation code between sun display, and other FG sections that use this
/* for things like lighting.
/*
* Revision 1.6 1998/02/07 15:29:32 curt
* Incorporated HUD changes and struct/typedef changes from Charlie Hotchkiss
* <chotchkiss@namg.us.anritsu.com>
*
* Revision 1.5 1998/02/02 20:53:21 curt
* To version 0.29
*
* Revision 1.4 1998/01/27 00:47:46 curt
* Incorporated Paul Bleisch's <bleisch@chromatic.com> new debug message
* system and commandline/config file processing code.
*
* Revision 1.3 1998/01/19 19:26:57 curt
* Merged in make system changes from Bob Kuehne <rpk@sgi.com>
* This should simplify things tremendously.
*
* Revision 1.2 1998/01/19 18:40:16 curt
* Tons of little changes to clean up the code and to remove fatal errors
* when building with the c++ compiler.
*
* Revision 1.1 1998/01/07 03:16:16 curt
* Moved from .../Src/Scenery/ to .../Src/Astro/
*
* Revision 1.16 1998/01/06 01:20:24 curt
* Tweaks to help building with MSVC++
*
* Revision 1.15 1998/01/05 18:44:35 curt
* Add an option to advance/decrease time from keyboard.
*
* Revision 1.14 1997/12/30 20:47:50 curt
* Integrated new event manager with subsystem initializations.
*
* Revision 1.13 1997/12/30 16:41:00 curt
* Added log at end of file.
*
*/
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