158 lines
5.0 KiB
C
158 lines
5.0 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 <Astro/orbits.h>
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#include <Astro/planets.h>
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#include <Astro/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, int idx)
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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, R, s, ir, Nr, B, FV, ring_magn,
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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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/* Let's calculate the brightness of the planet */
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R = sqrt ( xg*xg + yg*yg + zg*zg);
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s = SolarPosition.dist;
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FV = acos( (r*r + R*R - s*s) / (2*r*R));
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FV *= 57.29578; /* convert radians to degrees */
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switch(idx)
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{
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case 2: /* mercury */
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result.magnitude = -0.36 + 5*log10( r*R ) + 0.027 * FV + 2.2E-13 * pow(FV, 6);
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break;
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case 3: /*venus */
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result.magnitude = -4.34 + 5*log10( r*R ) + 0.013 * FV + 4.2E-07 * pow(FV,3);
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break;
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case 4: /* mars */
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result.magnitude = -1.51 + 5*log10( r*R ) + 0.016 * FV;
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break;
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case 5: /* Jupiter */
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result.magnitude = -9.25 + 5*log10( r*R ) + 0.014 * FV;
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break;
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case 6: /* Saturn */
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ir = 0.4897394;
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Nr = 2.9585076 + 6.6672E-7*actTime;
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B = asin ( sin (result.Declination) * cos(ir) - cos(result.Declination) * sin (ir) * sin (result.RightAscension - Nr));
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ring_magn = -2.6 * sin (abs(B)) + 1.2 * pow(sin(B),2);
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result.magnitude = -9.0 + 5*log10( r*R ) + 0.044 * FV + ring_magn;
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break;
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case 7: /* Uranus */
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result.magnitude = -7.15 + 5*log10( r*R) + 0.001 * FV;
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break;
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case 8: /* Neptune */
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result.magnitude = -6.90 + 5*log10 (r*R) + 0.001 *FV;
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break;
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default:
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printf("index %d out of range !!!!\n", idx);
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}
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printf(" Planet found at %f (ra), %f (dec)\n",
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result.RightAscension, result.Declination);
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printf(" Geocentric dist %f\n"
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" Heliocentric dist %f\n"
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" Distance to the sun %f\n"
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" Phase angle %f\n"
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" Brightness %f\n", R, r, s, FV, result.magnitude);
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return result;
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}
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/* $Log$
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/* Revision 1.2 1998/01/19 19:26:59 curt
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/* Merged in make system changes from Bob Kuehne <rpk@sgi.com>
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/* This should simplify things tremendously.
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/*
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* Revision 1.1 1998/01/07 03:16:18 curt
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* Moved from .../Src/Scenery/ to .../Src/Astro/
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*
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* Revision 1.4 1997/12/30 20:47:52 curt
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* Integrated new event manager with subsystem initializations.
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*
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* Revision 1.3 1997/12/30 16:36:52 curt
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* Merged in Durk's changes ...
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*
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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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