void slaAmp ( double ra, double da, double date, double eq,
double *rm, double *dm )
/*
** - - - - - - -
** s l a A m p
** - - - - - - -
**
** Convert star RA,Dec from geocentric apparent to mean place.
**
** The mean coordinate system is the post IAU 1976 system,
** loosely called FK5.
**
** Given:
** ra double apparent RA (radians)
** da double apparent Dec (radians)
** date double TDB for apparent place (JD-2400000.5)
** eq double equinox: Julian epoch of mean place
**
** Returned:
** *rm double mean RA (radians)
** *dm double mean Dec (radians)
**
** References:
** 1984 Astronomical Almanac, pp B39-B41.
** (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)
**
** Notes:
**
** 1) The distinction between the required TDB and TT is always
** negligible. Moreover, for all but the most critical
** applications UTC is adequate.
**
** 2) Iterative techniques are used for the aberration and light
** deflection corrections so that the routines slaAmp (or
** slaAmpqk) and slaMap (or slaMapqk) are accurate inverses;
** even at the edge of the Sun's disc the discrepancy is only
** about 1 nanoarcsecond.
**
** 3) Where multiple apparent places are to be converted to mean
** places, for a fixed date and equinox, it is more efficient to
** use the slaMappa routine to compute the required parameters
** once, followed by one call to slaAmpqk per star.
**
** 4) The accuracy is limited by imperfections in the IAU 1976/1980
** models for precession and nutation. Corrections are tabulated
** in IERS Bulletin B and at the present epoch are of order 50 mas.
** An improved precession-nutation model can be introduced by
** using slaMappa and slaAmpqk (see the previous note) and
** replacing the precession-nutation matrix into the parameter
** array directly.
**
** 5) The accuracy is further limited by the routine slaEvp, called
** by slaMappa, which computes the Earth position and velocity
** using the methods of Stumpff. The maximum error is about
** 0.3 mas.
**
** Called: slaMappa, slaAmpqk
**
** Last revision: 8 May 2000
**
** Copyright P.T.Wallace. All rights reserved.
**
*/
{
double amprms[21]; /* Mean-to-apparent parameters */
slaMappa ( eq, date, amprms );
slaAmpqk ( ra, da, amprms, rm, dm );
}
void slaAmp ( double ra, double da, double date, double eq,
double *rm, double *dm )
/*
** - - - - - - -
** s l a A m p
** - - - - - - -
**
** Convert star RA,Dec from geocentric apparent to mean place.
**
** The mean coordinate system is the post IAU 1976 system,
** loosely called FK5.
**
** Given:
** ra double apparent RA (radians)
** da double apparent Dec (radians)
** date double TDB for apparent place (JD-2400000.5)
** eq double equinox: Julian epoch of mean place
**
** Returned:
** *rm double mean RA (radians)
** *dm double mean Dec (radians)
**
** References:
** 1984 Astronomical Almanac, pp B39-B41.
** (also Lederle & Schwan, Astron. Astrophys. 134, 1-6, 1984)
**
** Notes:
**
** 1) The distinction between the required TDB and the more
** accessible TT is always negligible. Moreover, for all
** but the most critical applications UTC is adequate.
**
** 2) The accuracy is limited by the routine slaEvp, called
** by slaMappa, which computes the Earth positions and
** velocities using the methods of Stumpff. The maximum
** error is about 0.3 milliarcsecond.
**
** 3) Iterative techniques are used for the aberration and
** light deflection corrections so that the routines
** slaAmp (or slaAmpqk) and slaMap (or slaMapqk) are
** accurate inverses; even at the edge of the Sun's disc
** the discrepancy is only about 1 nanoarcsecond.
**
** 4) Where multiple apparent places are to be converted to
** mean places, for a fixed date and equinox, it is more
** efficient to use the slaMappa routine to compute the
** required parameters once, followed by one call to
** slaAmpqk per star.
**
** Called: slaMappa, slaAmpqk
**
** Last revision: 12 June 1996
**
** Copyright P.T.Wallace. All rights reserved.
**
*/
{
double amprms[21]; /* Mean-to-apparent parameters */
slaMappa ( eq, date, amprms );
slaAmpqk ( ra, da, amprms, rm, dm );
}
int
observed_altaz_to_mean_radec( const Site *site, double freq_ghz,
int n, const double ctime[],
const float alt[], const float az[],
float ra[], float dec[] )
{
assert( n > 0 );
assert( ctime != NULL );
assert( alt != NULL );
assert( az != NULL );
assert( ra != NULL );
assert( dec != NULL );
int stat;
float dut1, x, y;
double amprms[21], aoprms[14];
double utc = convert_ctime_to_utc_mjd( ctime[0] );
int mjd = (int) floor(utc);
stat = get_iers_bulletin_a( mjd, &dut1, &x, &y );
if ( stat != 0 )
return stat;
//printf( "mjd,dut1,x,y = %d, %g, %g, %g\n", mjd, dut1, x, y );
double wavelength_um = 299792.458/freq_ghz;
slaAoppa( utc, dut1,
site->east_longitude,
site->latitude,
site->elevation_m,
arcsec2rad(x),
arcsec2rad(y),
site->temperature_K,
site->pressure_mb,
site->relative_humidity,
wavelength_um,
0.0065, // tropospheric lapse rate [K/m]
aoprms );
double tt = convert_utc_to_tt( utc );
slaMappa( 2000.0, tt, amprms );
//printf( "freq = %g\n", freq_ghz );
for ( int i = 0; i < n; i++ )
{
double observed_az = az[i];
double observed_zenith = M_PI/2 - alt[i];
double apparent_ra, apparent_dec, mean_ra, mean_dec;
utc = convert_ctime_to_utc_mjd( ctime[i] );
slaAoppat( utc, aoprms );
slaOapqk( "A", observed_az, observed_zenith, aoprms,
&apparent_ra, &apparent_dec );
//printf( "apparent ra,dec = %g, %g\n", apparent_ra, apparent_dec );
slaAmpqk( apparent_ra, apparent_dec, amprms, &mean_ra, &mean_dec );
//printf( "mean ra,dec = %g, %g\n", mean_ra, mean_dec );
ra[i] = mean_ra;
dec[i] = mean_dec;
}
return 0;
}
