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;
}
void slaAoppa ( double date, double dut, double elongm, double phim,
double hm, double xp, double yp, double tdk,
double pmb, double rh, double wl, double tlr,
double aoprms[14] )
/*
** - - - - - - - - -
** s l a A o p p a
** - - - - - - - - -
**
** Precompute apparent to observed place parameters required by
** slaAopqk and slaOapqk.
**
** Given:
** date d UTC date/time (Modified Julian Date, JD-2400000.5)
** dut d delta UT: UT1-UTC (UTC seconds)
** elongm d mean longitude of the observer (radians, east +ve)
** phim d mean geodetic latitude of the observer (radians)
** hm d observer's height above sea level (metres)
** xp d polar motion x-coordinate (radians)
** yp d polar motion y-coordinate (radians)
** tdk d local ambient temperature (DegK; std=273.155)
** pmb d local atmospheric pressure (mB; std=1013.25)
** rh d local relative humidity (in the range 0.0-1.0)
** wl d effective wavelength (micron, e.g. 0.55)
** tlr d tropospheric lapse rate (DegK/metre, e.g. 0.0065)
**
** Returned:
** aoprms d[14] star-independent apparent-to-observed parameters:
**
** (0) geodetic latitude (radians)
** (1,2) sine and cosine of geodetic latitude
** (3) magnitude of diurnal aberration vector
** (4) height (hm)
** (5) ambient temperature (tdk)
** (6) pressure (pmb)
** (7) relative humidity (rh)
** (8) wavelength (wl)
** (9) lapse rate (tlr)
** (10,11) refraction constants A and B (radians)
** (12) longitude + eqn of equinoxes + sidereal DUT (radians)
** (13) local apparent sidereal time (radians)
**
** Notes:
**
** 1) It is advisable to take great care with units, as even
** unlikely values of the input parameters are accepted and
** processed in accordance with the models used.
**
** 2) The date argument is UTC expressed as an MJD. This is,
** strictly speaking, improper, because of leap seconds. However,
** as long as the delta UT and the UTC are consistent there
** are no difficulties, except during a leap second. In this
** case, the start of the 61st second of the final minute should
** begin a new MJD day and the old pre-leap delta UT should
** continue to be used. As the 61st second completes, the MJD
** should revert to the start of the day as, simultaneously,
** the delta UTC changes by one second to its post-leap new value.
**
** 3) The delta UT (UT1-UTC) is tabulated in IERS circulars and
** elsewhere. It increases by exactly one second at the end of
** each UTC leap second, introduced in order to keep delta UT
** within +/- 0.9 seconds.
**
** 4) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
** The longitude required by the present routine is east-positive,
** in accordance with geographical convention (and right-handed).
** In particular, note that the longitudes returned by the
** slaObs routine are west-positive, following astronomical
** usage, and must be reversed in sign before use in the present
** routine.
**
** 5) The polar coordinates xp,yp can be obtained from IERS
** circulars and equivalent publications. The maximum amplitude
** is about 0.3 arcseconds. If xp,yp values are unavailable,
** use xp=yp=0.0. See page B60 of the 1988 Astronomical Almanac
** for a definition of the two angles.
**
** 6) The height above sea level of the observing station, hm,
** can be obtained from the Astronomical Almanac (Section J
** in the 1988 edition), or via the routine slaObs. If p,
** the pressure in millibars, is available, an adequate
** estimate of hm can be obtained from the expression
**
** hm = -29.3 * tsl * log ( p / 1013.25 );
**
** where tsl is the approximate sea-level air temperature
** in deg K (See Astrophysical Quantities, C.W.Allen,
** 3rd edition, section 52). Similarly, if the pressure p
** is not known, it can be estimated from the height of the
** observing station, hm as follows:
**
** p = 1013.25 * exp ( -hm / ( 29.3 * tsl ) );
**
** Note, however, that the refraction is proportional to the
** pressure and that an accurate p value is important for
** precise work.
**
** 7) Repeated, computationally-expensive, calls to slaAoppa for
** times that are very close together can be avoided by calling
** slaAoppa just once and then using slaAoppat for the subsequent
** times. Fresh calls to slaAoppa will be needed only when changes
** in the precession have grown to unacceptable levels or when
** anything affecting the refraction has changed.
**
** Defined in slamac.h: D2PI, DS2R
**
** Called: slaGeoc, slaRefco, slaEqeqx, slaAoppat
**
** Last revision: 6 September 1999
**
** Copyright P.T.Wallace. All rights reserved.
*/
#define C 173.14463331 /* Speed of light (AU per day) */
#define SOLSID 1.00273790935 /* Ratio between solar and sidereal time */
{
double cphim, xt, yt, zt, xc, yc, zc, elong, phi, uau, vau;
/* Observer's location corrected for polar motion */
cphim = cos( phim );
xt = cos ( elongm ) * cphim;
yt = sin ( elongm ) * cphim;
zt = sin ( phim );
xc = xt - xp * zt;
yc = yt + yp * zt;
zc = xp * xt - yp * yt + zt;
elong = ( ( xc == 0.0 ) && ( yc == 0.0 ) ) ? 0.0 : atan2 ( yc, xc );
phi = atan2 ( zc, sqrt ( xc * xc + yc * yc ) );
aoprms[0] = phi;
aoprms[1] = sin ( phi );
aoprms[2] = cos ( phi );
/* Magnitude of the diurnal aberration vector */
slaGeoc ( phi, hm, &uau, &vau );
aoprms[3] = D2PI * uau * SOLSID / C;
/* Copy the refraction parameters and compute the A & B constants */
aoprms[4] = hm;
aoprms[5] = tdk;
aoprms[6] = pmb;
aoprms[7] = rh;
aoprms[8] = wl;
aoprms[9] = tlr;
slaRefco ( hm, tdk, pmb, rh, wl, phi, tlr, 1e-10,
&aoprms[10], &aoprms[11] );
/* Longitude + equation of the equinoxes + sidereal equivalent of DUT */
aoprms[12] = elong + slaEqeqx ( date ) + dut * SOLSID * DS2R;
/* Sidereal time */
slaAoppat ( date, aoprms );
}
