94 lines
2.9 KiB
C
94 lines
2.9 KiB
C
/**************************************************************************
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* planets.c
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*
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* Written 1997 by Durk Talsma, started October, 1997. For the flight gear
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* project.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License as
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* published by the Free Software Foundation; either version 2 of the
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* License, or (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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*
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* $Id$
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* (Log is kept at end of this file)
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**************************************************************************/
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#include "../Time/fg_time.h"
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#include "orbits.h"
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#include "planets.h"
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#include "sun.h"
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struct CelestialCoord fgCalculatePlanet(struct OrbElements planet,
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struct OrbElements theSun,
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struct fgTIME t)
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{
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struct CelestialCoord
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result;
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struct SunPos
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SolarPosition;
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double
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eccAnom, r, v, ecl, actTime,
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xv, yv, xh, yh, zh, xg, yg, zg, xe, ye, ze;
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actTime = fgCalcActTime(t);
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/* calculate the angle between ecliptic and equatorial coordinate system */
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ecl = fgDegToRad(23.4393 - 3.563E-7 * actTime);
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/* calculate the eccentric anomaly */
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eccAnom = fgCalcEccAnom(planet.M, planet.e);
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/* calculate the planets distance (r) and true anomaly (v) */
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xv = planet.a * (cos(eccAnom) - planet.e);
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yv = planet.a * (sqrt(1.0 - planet.e*planet.e) * sin(eccAnom));
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v = atan2(yv, xv);
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r = sqrt ( xv*xv + yv*yv);
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/* calculate the planets position in 3-dimensional space */
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xh = r * ( cos(planet.N) * cos(v+planet.w) - sin(planet.N) * sin(v+planet.w) * cos(planet.i));
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yh = r * ( sin(planet.N) * cos(v+planet.w) + cos(planet.N) * sin(v+planet.w) * cos(planet.i));
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zh = r * ( sin(v+planet.w) * sin(planet.i));
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/* calculate the ecleptic longitude and latitude */
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/*
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lonecl = atan2(yh, xh);
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latecl = atan2(zh, sqrt ( xh*xh + yh*yh));
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*/
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/* calculate the solar position */
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SolarPosition = fgCalcSunPos(theSun);
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xg = xh + SolarPosition.xs;
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yg = yh + SolarPosition.ys;
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zg = zh;
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xe = xg;
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ye = yg * cos(ecl) - zg * sin(ecl);
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ze = yg * sin(ecl) + zg * cos(ecl);
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result.RightAscension = atan2(ye,xe);
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result.Declination = atan2(ze, sqrt(xe*xe + ye*ye));
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return result;
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}
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/* $Log$
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/* Revision 1.2 1997/12/12 21:41:29 curt
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/* More light/material property tweaking ... still a ways off.
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/*
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* Revision 1.1 1997/10/25 03:16:10 curt
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* Initial revision of code contributed by Durk Talsma.
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*
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*/
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