flightgear/Astro/planets.c

/**************************************************************************
 * planets.c
 *
 * Written 1997 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)
 **************************************************************************/


#ifdef WIN32
#  include <windows.h>
#endif

#include <GL/glut.h>
#include <XGL/xgl.h>

#include <Time/fg_time.h>
#include <Astro/orbits.h>
#include <Astro/planets.h>
#include <Astro/sun.h>
#include <Include/fg_constants.h>
#include <Main/fg_debug.h>

GLint planets = 0;

struct CelestialCoord fgCalculatePlanet(struct OrbElements planet,
                                        struct OrbElements theSun,
                                        struct fgTIME t, int idx)
{
   struct CelestialCoord
		result;

    struct SunPos
    	SolarPosition;

	double
        eccAnom, r, v, ecl, actTime, R, s, ir, Nr, B, FV, ring_magn,
        xv, yv, xh, yh, zh, xg, yg, zg, xe, ye, ze;

      actTime = fgCalcActTime(t);
      /* calculate the angle between ecliptic and equatorial coordinate system */
      /* ecl = DEG_TO_RAD * (23.4393 - 3.563E-7 * actTime); */
      ecl = 0.409093 - 6.2186E-9 * actTime;

    /* calculate the eccentric anomaly */
	eccAnom  = fgCalcEccAnom(planet.M, planet.e);

    /* calculate the planets distance (r) and true anomaly (v) */
    xv = planet.a * (cos(eccAnom) - planet.e);
    yv = planet.a * (sqrt(1.0 - planet.e*planet.e) * sin(eccAnom));
    v = atan2(yv, xv);
    r = sqrt ( xv*xv + yv*yv);

    /* calculate the planets position in 3-dimensional space */
    xh = r * ( cos(planet.N) * cos(v+planet.w) - sin(planet.N) * sin(v+planet.w) * cos(planet.i));
    yh = r * ( sin(planet.N) * cos(v+planet.w) + cos(planet.N) * sin(v+planet.w) * cos(planet.i));
    zh = r * ( sin(v+planet.w) * sin(planet.i));

    /* calculate the ecliptic longitude and latitude */

    /*
    lonecl = atan2(yh, xh);
    latecl = atan2(zh, sqrt ( xh*xh + yh*yh));
    */
    /* calculate the solar position */

    SolarPosition = fgCalcSunPos(theSun);
    xg = xh + SolarPosition.xs;
    yg = yh + SolarPosition.ys;
    zg = zh;

    xe = xg;
    ye = yg * cos(ecl) - zg * sin(ecl);
    ze = yg * sin(ecl) + zg * cos(ecl);

    result.RightAscension = atan2(ye,xe);
    result.Declination = atan2(ze, sqrt(xe*xe + ye*ye));

	 
    /* Let's calculate the brightness of the planet */
    R = sqrt ( xg*xg + yg*yg + zg*zg);
    s = SolarPosition.dist;
    FV = acos(  (r*r + R*R - s*s) / (2*r*R));
    FV  *= 57.29578;  /* convert radians to degrees */ 
    switch(idx)
      {
      case 2: /* mercury */
	result.magnitude = -0.36 + 5*log10( r*R ) + 0.027 * FV + 2.2E-13 * pow(FV, 6);
	break;
      case 3: /*venus */
	result.magnitude = -4.34 + 5*log10( r*R ) + 0.013 * FV + 4.2E-07 * pow(FV,3);
	break;
      case 4: /* mars */
	result.magnitude = -1.51 + 5*log10( r*R ) + 0.016 * FV;
	break;
      case 5: /* Jupiter */
	result.magnitude = -9.25 + 5*log10( r*R ) + 0.014 * FV;
	break;
      case 6: /* Saturn */
	
	ir = 0.4897394;
	Nr = 2.9585076 + 6.6672E-7*actTime;
	
	B = asin ( sin (result.Declination) * cos(ir) - cos(result.Declination) * sin (ir) * sin (result.RightAscension - Nr));
	ring_magn = -2.6 * sin (abs(B)) + 1.2 * pow(sin(B),2);
	result.magnitude = -9.0 + 5*log10( r*R ) + 0.044 * FV + ring_magn;
	break;
      case 7: /* Uranus */
	result.magnitude = -7.15 + 5*log10( r*R) + 0.001 * FV;
	break;
      case 8:  /* Neptune */
	result.magnitude = -6.90 + 5*log10 (r*R) + 0.001 *FV;
	break;
      default:
	fgPrintf( FG_ASTRO, FG_ALERT, "index %d out of range !!!!\n", idx);
      }
    fgPrintf( FG_ASTRO, FG_DEBUG,
	      "    Planet found at %f (ra), %f (dec)\n", 
	      result.RightAscension, result.Declination);
    fgPrintf( FG_ASTRO, FG_DEBUG,
	      "      Geocentric dist     %f\n"
	      "      Heliocentric dist   %f\n"
	      "      Distance to the sun %f\n"
	      "      Phase angle         %f\n"
	      "      Brightness          %f\n", R, r, s, FV, result.magnitude);
    return result;
}


void fgPlanetsInit( void )
{
  int i;
  struct CelestialCoord pltPos;
  double magnitude;

  /* if the display list was already built during a previous init,
     recycle it */

  if (planets)
      xglDeleteLists(planets, 1);

  planets = xglGenLists(1);
  xglNewList( planets, GL_COMPILE );
  xglBegin( GL_POINTS );


  /* Add the planets to all four display lists */
  for ( i = 2; i < 9; i++ ) {
    fgSolarSystemUpdate(&(pltOrbElements[i]), cur_time_params);
    pltPos = fgCalculatePlanet(pltOrbElements[i], 
			       pltOrbElements[0], cur_time_params, i);
    
    /* give the planets a temporary color, for testing purposes */
    /* xglColor3f( 1.0, 0.0, 0.0); */
    /* scale magnitudes to (0.0 - 1.0) */
    
    magnitude = (0.0 - pltPos.magnitude) / 5.0 + 1.0;
    
    /* scale magnitudes again so they look ok */
    /* magnitude = 
       magnitude * 0.7 + (((FG_STAR_LEVELS - 1) - i) * 0.1); */

    /* the following statement could be made a little more sopisticated
       for the moment: Stick to this one */
    magnitude = magnitude * 0.7 + (3 * 0.1);
    if ( magnitude > 1.0 ) { magnitude = 1.0; }
    if ( magnitude < 0.0 ) { magnitude = 0.0; }
    
    
    xglColor3f(magnitude, magnitude, magnitude);
    /* xglColor3f(1.0, 1.0,1.0); */
    
    xglVertex3f( 50000.0 * cos(pltPos.RightAscension) * 
		           cos(pltPos.Declination),
		 50000.0 * sin(pltPos.RightAscension) * 
		           cos(pltPos.Declination),
		 50000.0 * sin(pltPos.Declination) );
  }
  xglEnd();
  xglEndList();

}


void fgPlanetsRender( void ) {
	xglCallList(planets);
}


/* $Log$
/* Revision 1.4  1998/02/02 20:53:23  curt
/* To version 0.29
/*
 * Revision 1.3  1998/01/27 00:47:47  curt
 * Incorporated Paul Bleisch's <bleisch@chromatic.com> new debug message
 * system and commandline/config file processing code.
 *
 * Revision 1.2  1998/01/19 19:26:59  curt
 * Merged in make system changes from Bob Kuehne <rpk@sgi.com>
 * This should simplify things tremendously.
 *
 * Revision 1.1  1998/01/07 03:16:18  curt
 * Moved from .../Src/Scenery/ to .../Src/Astro/
 *
 * Revision 1.4  1997/12/30 20:47:52  curt
 * Integrated new event manager with subsystem initializations.
 *
 * Revision 1.3  1997/12/30 16:36:52  curt
 * Merged in Durk's changes ...
 *
 * Revision 1.2  1997/12/12 21:41:29  curt
 * More light/material property tweaking ... still a ways off.
 *
 * Revision 1.1  1997/10/25 03:16:10  curt
 * Initial revision of code contributed by Durk Talsma.
 *
 */