/*************************************************************************
Description:
This function uses the NOVAS software library to compute the position
of the Sun on the local horizon, but for an input time, instead of the
current time.
Inputs:
here - The point on the surface of the earth we are at.
time_in - The UTC time in seconds that we need to compute
the Sun's position.
Outputs:
*SunAz - The returned sun azimuth, in degrees from true north.
*SunEl - The returned sun elevation, in degrees above the
local horizon.
**************************************************************************/
void ORPGSUN_NovasComputePosAtTime( site_info here, double *SunAz,
double *SunEl, time_t time_in ){
/* The earth and sun body structures. See NOVAS documentation for
more information. */
body earth, sun;
/* The right ascension, and declination of the sun */
double ra, declination;
/* The terrestrial dynamical time (TDT) julian date */
double tdt_julian_date;
/* Zenith distance, measured from the local vertical. */
double zenith_distance;
/* The Sun's azimuth is measured from the north */
double azimuth;
/* rar -right ascension. decr -declination. In equatorial
coordinate system */
double rar, decr;
/* The distance to the Sun, units of AU, not returned by this function. */
double distanceAU;
/* Call NOVAS subroutine set_body to setup Sun and Earth body structures. */
set_body( 0, 10, "Sun", &sun );
set_body( 0, 3, "Earth", &earth );
/* Get the TDT date for the input time. */
Get_tdt_julian_date_at_time( &tdt_julian_date, time_in, ORPGSUN_DELTAT );
/* Call NOVAS routine topo_planet to get the right ascension and
declination of the Sun in topographic/equatorial coordinate
system. */
topo_planet( tdt_julian_date, &sun, &earth, ORPGSUN_DELTAT, &here,
&ra, &declination, &distanceAU );
/* Call NOVAS subroutine equ2hor to convert the Sun's position to
local horizon coordinates. */
equ2hor( tdt_julian_date, ORPGSUN_DELTAT,
0.0 /* x_ephemeris */,
0.0 /* y_ephemeris */,
&here, ra, declination, 1 /* normal refraction */,
&zenith_distance,
&azimuth,
&rar, &decr );
/* Convert zenith_distance reference point so that the Sun's
elevation is referenced to the local horizon. */
*SunEl = 90.0 - zenith_distance;
/* Azimuth needs no conversion, its local horizon reference
is already true north. */
*SunAz = azimuth;
} /* End of ORPGSUN_NovasComputePosAtTime() */
/**
* This function uses the NOVAS software library to compute the position
* of the Sun on the local horizon, but for an input time, instead of the current time.
*
* --------------------------------------------------------
*
* @param here (site_info) The point on the surface of the earth we are at.
* @param deltat (double) The difference between terrestrial dynamical time system 1 time, and universal time.
* @param *SunAz (double *) The returned sun azimuth, in degrees from true north.
* @param *SunEl (double *) The returned sun elevation, in degrees above the local horizon.
* @param time_in (time_t) The utc time in seconds that we need to compute the Sun's position.
*
* --------------------------------------------------------
*/
void rsts_SunNovasComputePosAtTime( site_info here, double deltat, double *SunAz, double *SunEl, time_t time_in )
{
/** <b> Local Variables </b> */
/** <ul> */
/** <li><b> body earth,sun </b> - The earth and sun body structures. See NOVAS documentation for more information. </li> */
body earth,sun;
/** <li><b> double ra,declination </b> - The right ascension, and declination of the sun </li> */
double ra,declination;
/** <li><b> double tdt_julian_date </b> - the current terrestrial dynamical time (TDT) julian date </li> */
double tdt_julian_date;
/** <li><b> double zenith_distance </b> - Zenith distance, measured from the local vertical. </li> */
double zenith_distance;
/** <li><b> double azimuth </b> - The Sun's azimuth is measured from the north </li> */
double azimuth;
/** <li><b> double rar,decr </b> - rar -right ascension. decr -declination. In equatorial coordinate system </li> */
double rar,decr;
/** <li><b> double distanceAU </b> - The distance to the Sun, units of AU, not returned by this function. </li> */
double distanceAU;
/** </ul> */
/**------------------------------------------------------*/
/** <h3> The following is a detailed description of the steps for rsts_SunNovasComputePosAtTime(): </h3> */
/** Call NOVAS subroutine set_body to setup Sun and Earth body structures. */
set_body(0,10,"Sun",&sun);
set_body(0,3,"Earth",&earth);
/** Get the TDT date for the input time. */
rsts_get_tdt_julian_date_at_time( &tdt_julian_date, time_in);
/** Call NOVOS routine topo_planet to get the right ascension and declination
* of the Sun in topographic/equatorial coordinate system. */
topo_planet( tdt_julian_date,
&sun, &earth, deltat,
&here ,
&ra , &declination , &distanceAU);
/** Call NOVAS subroutine equ2hor to convert the Sun's position to local horizon coordinates. */
equ2hor( tdt_julian_date, deltat,
0.0 /*x_ephemeris*/, 0.0 /*y_ephemeris*/,
&here,ra,declination,1/*normal refraction*/,
&zenith_distance,
&azimuth,
&rar,&decr);
/** Convert zenith_distance reference point so that the Sun's elevation is referenced to the local horizon. */
*SunEl = 90.0 - zenith_distance;
/** Azimuth needs no conversion, its local horizon reference is already true north. */
*SunAz = azimuth;
/** Log a message to the test log with the input time, and position of the sun given. */
/** RSTS_LOG_MSG(LOG_RDA_OTEST,"Sun Pos at TDT JD %f - Az %f El %f",tdt_julian_date,*SunAz,*SunEl); */
/** If this is a stand alone unit test, the results of the subroutine are printed
* for comparison with the naval observatory's web pages. */
#ifdef _RSTS_SUN_POS_UNIT_TEST
printf(" El : %f Az : %f \n", *SunEl, *SunAz);
#endif
}
