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kstars

kscomet.cpp

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/***************************************************************************
                          kscomet.cpp  -  K Desktop Planetarium
                             -------------------
    begin                : Wed 19 Feb 2003
    copyright            : (C) 2001 by Jason Harris
    email                : jharris@30doradus.org
 ***************************************************************************/

/***************************************************************************
 *                                                                         *
 *   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.                                   *
 *                                                                         *
 ***************************************************************************/

#include <kdebug.h>

#include "kstarsdata.h"
#include "kstarsdatetime.h"
#include "ksnumbers.h"
#include "dms.h"
#include "kscomet.h"


KSComet::KSComet( KStarsData *_kd, QString _s, QString imfile,
        long double _JD, double _q, double _e, dms _i, dms _w, dms _Node, double Tp )
 : KSPlanetBase(_kd, _s, imfile), kd(_kd), JD(_JD), q(_q), e(_e), i(_i), w(_w), N(_Node) {

    setType( 9 ); //Comet

    //Find the Julian Day of Perihelion from Tp
    //Tp is a double which encodes a date like: YYYYMMDD.DDDDD (e.g., 19730521.33333
    int year = int( Tp/10000.0 );
    int month = int( (int(Tp) % 10000)/100.0 );
    int day = int( int(Tp) % 100 );
    double Hour = 24.0 * ( Tp - int(Tp) );
    int h = int( Hour );
    int m = int( 60.0 * ( Hour - h ) );
    int s = int( 60.0 * ( 60.0 * ( Hour - h) - m ) );

    JDp = KStarsDateTime( ExtDate( year, month, day ), QTime( h, m, s ) ).djd();

    //compute the semi-major axis, a:
    a = q/(1.0-e);

    //Compute the orbital Period from Kepler's 3rd law:
    P = 365.2568984 * pow(a, 1.5); //period in days

    //If the name contains a "/", make this name2 and make name a truncated version without the leading "P/" or "C/"
    if ( name().contains( "/" ) ) {
        setLongName( name() );
        setName( name().mid( name().find("/") + 1 ) );
    }
}

bool KSComet::findGeocentricPosition( const KSNumbers *num, const KSPlanetBase *Earth ) {
    double v(0.0), r(0.0);

    //Precess the longitude of the Ascending Node to the desired epoch:
    dms n = dms( double(N.Degrees() - 3.82394E-5 * ( num->julianDay() - J2000 )) ).reduce();

    if ( e > 0.98 ) {
        //Use near-parabolic approximation
        double k = 0.01720209895; //Gauss gravitational constant
        double a = 0.75 * ( num->julianDay() - JDp ) * k * sqrt( (1+e)/(q*q*q) );
        double b = sqrt( 1.0 + a*a );
        double W = pow((b+a),1.0/3.0) - pow((b-a),1.0/3.0);
        double c = 1.0 + 1.0/(W*W);
        double f = (1.0-e)/(1.0+e);
        double g = f/(c*c);

        double a1 = (2.0/3.0) + (2.0*W*W/5.0);
        double a2 = (7.0/5.0) + (33.0*W*W/35.0) + (37.0*W*W*W*W/175.0);
        double a3 = W*W*( (432.0/175.0) + (956.0*W*W/1125.0) + (84.0*W*W*W*W/1575.0) );
        double w = W*(1.0 + g*c*( a1 + a2*g + a3*g*g ));

        v = 2.0*atan(w) / dms::DegToRad;
        r = q*( 1.0 + w*w )/( 1.0 + w*w*f );
    } else {
        //Use normal ellipse method
        //Determine Mean anomaly for desired date:
        dms m = dms( double(360.0*( num->julianDay() - JDp )/P) ).reduce();
        double sinm, cosm;
        m.SinCos( sinm, cosm );

        //compute eccentric anomaly:
        double E = m.Degrees() + e*180.0/dms::PI * sinm * ( 1.0 + e*cosm );

        if ( e > 0.05 ) { //need more accurate approximation, iterate...
            double E0;
            int iter(0);
            do {
                E0 = E;
                iter++;
                E = E0 - ( E0 - e*180.0/dms::PI *sin( E0*dms::DegToRad ) - m.Degrees() )/(1 - e*cos( E0*dms::DegToRad ) );
            } while ( fabs( E - E0 ) > 0.001 && iter < 1000 );
        }

        double sinE, cosE;
        dms E1( E );
        E1.SinCos( sinE, cosE );

        double xv = a * ( cosE - e );
        double yv = a * sqrt( 1.0 - e*e ) * sinE;

        //v is the true anomaly; r is the distance from the Sun

        v = atan( yv/xv ) / dms::DegToRad;
        //resolve atan ambiguity
        if ( xv < 0.0 ) v += 180.0;

        r = sqrt( xv*xv + yv*yv );
    }

    //vw is the sum of the true anomaly and the argument of perihelion
    dms vw( v + w.Degrees() );
    double sinN, cosN, sinvw, cosvw, sini, cosi;

    n.SinCos( sinN, cosN );
    vw.SinCos( sinvw, cosvw );
    i.SinCos( sini, cosi );

    //xh, yh, zh are the heliocentric cartesian coords with the ecliptic plane congruent with zh=0.
    double xh = r * ( cosN * cosvw - sinN * sinvw * cosi );
    double yh = r * ( sinN * cosvw + cosN * sinvw * cosi );
    double zh = r * ( sinvw * sini );

    //xe, ye, ze are the Earth's heliocentric cartesian coords
    double cosBe, sinBe, cosLe, sinLe;
    Earth->ecLong()->SinCos( sinLe, cosLe );
    Earth->ecLat()->SinCos( sinBe, cosBe );

    double xe = Earth->rsun() * cosBe * cosLe;
    double ye = Earth->rsun() * cosBe * sinLe;
    double ze = Earth->rsun() * sinBe;

    //convert to geocentric ecliptic coordinates by subtracting Earth's coords:
    xh -= xe;
    yh -= ye;
    zh -= ze;

    //Finally, the spherical ecliptic coordinates:
    double ELongRad = atan( yh/xh );
    //resolve atan ambiguity
    if ( xh < 0.0 ) ELongRad += dms::PI;

    double rr = sqrt( xh*xh + yh*yh );
    double ELatRad = atan( zh/rr );  //(rr can't possibly be negative, so no atan ambiguity)

    ep.longitude.setRadians( ELongRad );
    ep.latitude.setRadians( ELatRad );
    setRsun( r );
    setRearth( Earth );
    
    EclipticToEquatorial( num->obliquity() );
    nutate( num );
    aberrate( num );

    return true;
}

//Unused virtual function from KSPlanetBase
bool KSComet::loadData() { return false; }

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