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166 lines
5.5 KiB
166 lines
5.5 KiB
/***************************************************************************
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kscomet.cpp - Trinity Desktop Planetarium
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-------------------
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begin : Wed 19 Feb 2003
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copyright : (C) 2001 by Jason Harris
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email : jharris@30doradus.org
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***************************************************************************/
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/***************************************************************************
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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***************************************************************************/
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#include <kdebug.h>
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#include "kstarsdata.h"
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#include "kstarsdatetime.h"
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#include "ksnumbers.h"
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#include "dms.h"
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#include "kscomet.h"
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KSComet::KSComet( KStarsData *_kd, TQString _s, TQString imfile,
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long double _JD, double _q, double _e, dms _i, dms _w, dms _Node, double Tp )
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: KSPlanetBase(_kd, _s, imfile), kd(_kd), JD(_JD), q(_q), e(_e), i(_i), w(_w), N(_Node) {
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setType( 9 ); //Comet
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//Find the Julian Day of Perihelion from Tp
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//Tp is a double which encodes a date like: YYYYMMDD.DDDDD (e.g., 19730521.33333
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int year = int( Tp/10000.0 );
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int month = int( (int(Tp) % 10000)/100.0 );
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int day = int( int(Tp) % 100 );
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double Hour = 24.0 * ( Tp - int(Tp) );
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int h = int( Hour );
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int m = int( 60.0 * ( Hour - h ) );
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int s = int( 60.0 * ( 60.0 * ( Hour - h) - m ) );
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JDp = KStarsDateTime( ExtDate( year, month, day ), TQTime( h, m, s ) ).djd();
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//compute the semi-major axis, a:
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a = q/(1.0-e);
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//Compute the orbital Period from Kepler's 3rd law:
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P = 365.2568984 * pow(a, 1.5); //period in days
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//If the name contains a "/", make this name2 and make name a truncated version without the leading "P/" or "C/"
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if ( name().contains( "/" ) ) {
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setLongName( name() );
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setName( name().mid( name().find("/") + 1 ) );
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}
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}
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bool KSComet::findGeocentricPosition( const KSNumbers *num, const KSPlanetBase *Earth ) {
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double v(0.0), r(0.0);
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//Precess the longitude of the Ascending Node to the desired epoch:
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dms n = dms( double(N.Degrees() - 3.82394E-5 * ( num->julianDay() - J2000 )) ).reduce();
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if ( e > 0.98 ) {
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//Use near-parabolic approximation
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double k = 0.01720209895; //Gauss gravitational constant
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double a = 0.75 * ( num->julianDay() - JDp ) * k * sqrt( (1+e)/(q*q*q) );
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double b = sqrt( 1.0 + a*a );
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double W = pow((b+a),1.0/3.0) - pow((b-a),1.0/3.0);
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double c = 1.0 + 1.0/(W*W);
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double f = (1.0-e)/(1.0+e);
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double g = f/(c*c);
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double a1 = (2.0/3.0) + (2.0*W*W/5.0);
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double a2 = (7.0/5.0) + (33.0*W*W/35.0) + (37.0*W*W*W*W/175.0);
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double a3 = W*W*( (432.0/175.0) + (956.0*W*W/1125.0) + (84.0*W*W*W*W/1575.0) );
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double w = W*(1.0 + g*c*( a1 + a2*g + a3*g*g ));
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v = 2.0*atan(w) / dms::DegToRad;
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r = q*( 1.0 + w*w )/( 1.0 + w*w*f );
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} else {
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//Use normal ellipse method
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//Determine Mean anomaly for desired date:
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dms m = dms( double(360.0*( num->julianDay() - JDp )/P) ).reduce();
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double sinm, cosm;
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m.SinCos( sinm, cosm );
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//compute eccentric anomaly:
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double E = m.Degrees() + e*180.0/dms::PI * sinm * ( 1.0 + e*cosm );
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if ( e > 0.05 ) { //need more accurate approximation, iterate...
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double E0;
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int iter(0);
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do {
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E0 = E;
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iter++;
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E = E0 - ( E0 - e*180.0/dms::PI *sin( E0*dms::DegToRad ) - m.Degrees() )/(1 - e*cos( E0*dms::DegToRad ) );
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} while ( fabs( E - E0 ) > 0.001 && iter < 1000 );
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}
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double sinE, cosE;
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dms E1( E );
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E1.SinCos( sinE, cosE );
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double xv = a * ( cosE - e );
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double yv = a * sqrt( 1.0 - e*e ) * sinE;
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//v is the true anomaly; r is the distance from the Sun
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v = atan( yv/xv ) / dms::DegToRad;
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//resolve atan ambiguity
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if ( xv < 0.0 ) v += 180.0;
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r = sqrt( xv*xv + yv*yv );
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}
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//vw is the sum of the true anomaly and the argument of perihelion
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dms vw( v + w.Degrees() );
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double sinN, cosN, sinvw, cosvw, sini, cosi;
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n.SinCos( sinN, cosN );
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vw.SinCos( sinvw, cosvw );
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i.SinCos( sini, cosi );
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//xh, yh, zh are the heliocentric cartesian coords with the ecliptic plane congruent with zh=0.
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double xh = r * ( cosN * cosvw - sinN * sinvw * cosi );
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double yh = r * ( sinN * cosvw + cosN * sinvw * cosi );
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double zh = r * ( sinvw * sini );
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//xe, ye, ze are the Earth's heliocentric cartesian coords
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double cosBe, sinBe, cosLe, sinLe;
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Earth->ecLong()->SinCos( sinLe, cosLe );
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Earth->ecLat()->SinCos( sinBe, cosBe );
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double xe = Earth->rsun() * cosBe * cosLe;
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double ye = Earth->rsun() * cosBe * sinLe;
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double ze = Earth->rsun() * sinBe;
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//convert to geocentric ecliptic coordinates by subtracting Earth's coords:
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xh -= xe;
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yh -= ye;
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zh -= ze;
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//Finally, the spherical ecliptic coordinates:
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double ELongRad = atan( yh/xh );
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//resolve atan ambiguity
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if ( xh < 0.0 ) ELongRad += dms::PI;
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double rr = sqrt( xh*xh + yh*yh );
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double ELatRad = atan( zh/rr ); //(rr can't possibly be negative, so no atan ambiguity)
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ep.longitude.setRadians( ELongRad );
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ep.latitude.setRadians( ELatRad );
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setRsun( r );
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setRearth( Earth );
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EclipticToEquatorial( num->obliquity() );
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nutate( num );
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aberrate( num );
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return true;
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}
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//Unused virtual function from KSPlanetBase
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bool KSComet::loadData() { return false; }
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