61 lines
1.9 KiB
C
61 lines
1.9 KiB
C
/**************************************************************************
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* sun.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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struct SunPos fgCalcSunPos(struct OrbElements params)
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{
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double
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EccAnom, lonSun,
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xv, yv, v, r;
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struct SunPos
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solarPosition;
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/* calculate the eccentric anomaly */
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EccAnom = fgCalcEccAnom(params.M, params.e);
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/* calculate the Suns distance (r) and its true anomaly (v) */
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xv = cos(EccAnom) - params.e;
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yv = sqrt(1.0 - params.e*params.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 the Suns true longitude (lonsun) */
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lonSun = v + params.w;
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/* convert true longitude and distance to ecliptic rectangular geocentric
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coordinates (xs, ys) */
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solarPosition.xs = r * cos(lonSun);
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solarPosition.ys = r * sin(lonSun);
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return solarPosition;
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}
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/* $Log$
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/* Revision 1.1 1997/10/25 03:16:11 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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