int eraAtoc13(const char *type, double ob1, double ob2,
double utc1, double utc2, double dut1,
double elong, double phi, double hm, double xp, double yp,
double phpa, double tc, double rh, double wl,
double *rc, double *dc)
/*
** - - - - - - - - - -
** e r a A t o c 1 3
** - - - - - - - - - -
**
** Observed place at a groundbased site to to ICRS astrometric RA,Dec.
** The caller supplies UTC, site coordinates, ambient air conditions
** and observing wavelength.
**
** Given:
** type char[] type of coordinates - "R", "H" or "A" (Notes 1,2)
** ob1 double observed Az, HA or RA (radians; Az is N=0,E=90)
** ob2 double observed ZD or Dec (radians)
** utc1 double UTC as a 2-part...
** utc2 double ...quasi Julian Date (Notes 3,4)
** dut1 double UT1-UTC (seconds, Note 5)
** elong double longitude (radians, east +ve, Note 6)
** phi double geodetic latitude (radians, Note 6)
** hm double height above ellipsoid (m, geodetic Notes 6,8)
** xp,yp double polar motion coordinates (radians, Note 7)
** phpa double pressure at the observer (hPa = mB, Note 8)
** tc double ambient temperature at the observer (deg C)
** rh double relative humidity at the observer (range 0-1)
** wl double wavelength (micrometers, Note 9)
**
** Returned:
** rc,dc double ICRS astrometric RA,Dec (radians)
**
** Returned (function value):
** int status: +1 = dubious year (Note 4)
** 0 = OK
** -1 = unacceptable date
**
** Notes:
**
** 1) "Observed" Az,ZD means the position that would be seen by a
** perfect geodetically aligned theodolite. (Zenith distance is
** used rather than altitude in order to reflect the fact that no
** allowance is made for depression of the horizon.) This is
** related to the observed HA,Dec via the standard rotation, using
** the geodetic latitude (corrected for polar motion), while the
** observed HA and RA are related simply through the Earth rotation
** angle and the site longitude. "Observed" RA,Dec or HA,Dec thus
** means the position that would be seen by a perfect equatorial
** with its polar axis aligned to the Earth's axis of rotation.
**
** 2) Only the first character of the type argument is significant.
** "R" or "r" indicates that ob1 and ob2 are the observed right
** ascension and declination; "H" or "h" indicates that they are
** hour angle (west +ve) and declination; anything else ("A" or
** "a" is recommended) indicates that ob1 and ob2 are azimuth
** (north zero, east 90 deg) and zenith distance.
**
** 3) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
** convenient way between the two arguments, for example where utc1
** is the Julian Day Number and utc2 is the fraction of a day.
**
** However, JD cannot unambiguously represent UTC during a leap
** second unless special measures are taken. The convention in the
** present function is that the JD day represents UTC days whether
** the length is 86399, 86400 or 86401 SI seconds.
**
** Applications should use the function eraDtf2d to convert from
** calendar date and time of day into 2-part quasi Julian Date, as
** it implements the leap-second-ambiguity convention just
** described.
**
** 4) The warning status "dubious year" flags UTCs that predate the
** introduction of the time scale or that are too far in the
** future to be trusted. See eraDat for further details.
**
** 5) UT1-UTC is tabulated in IERS bulletins. It increases by exactly
** one second at the end of each positive UTC leap second,
** introduced in order to keep UT1-UTC within +/- 0.9s. n.b. This
** practice is under review, and in the future UT1-UTC may grow
** essentially without limit.
**
** 6) The geographical coordinates are with respect to the ERFA_WGS84
** reference ellipsoid. TAKE CARE WITH THE LONGITUDE SIGN: the
** longitude required by the present function is east-positive
** (i.e. right-handed), in accordance with geographical convention.
**
** 7) The polar motion xp,yp can be obtained from IERS bulletins. The
** values are the coordinates (in radians) of the Celestial
** Intermediate Pole with respect to the International Terrestrial
** Reference System (see IERS Conventions 2003), measured along the
** meridians 0 and 90 deg west respectively. For many
** applications, xp and yp can be set to zero.
**
** 8) If hm, the height above the ellipsoid of the observing station
** in meters, is not known but phpa, the pressure in hPa (=mB), is
** available, an adequate estimate of hm can be obtained from the
** expression
**
** hm = -29.3 * tsl * log ( phpa / 1013.25 );
**
** where tsl is the approximate sea-level air temperature in K
** (See Astrophysical Quantities, C.W.Allen, 3rd edition, section
** 52). Similarly, if the pressure phpa is not known, it can be
** estimated from the height of the observing station, hm, as
** follows:
**
** phpa = 1013.25 * exp ( -hm / ( 29.3 * tsl ) );
**
** Note, however, that the refraction is nearly proportional to
** the pressure and that an accurate phpa value is important for
** precise work.
**
** 9) The argument wl specifies the observing wavelength in
** micrometers. The transition from optical to radio is assumed to
** occur at 100 micrometers (about 3000 GHz).
**
** 10) The accuracy of the result is limited by the corrections for
** refraction, which use a simple A*tan(z) + B*tan^3(z) model.
** Providing the meteorological parameters are known accurately and
** there are no gross local effects, the predicted astrometric
** coordinates should be within 0.05 arcsec (optical) or 1 arcsec
** (radio) for a zenith distance of less than 70 degrees, better
** than 30 arcsec (optical or radio) at 85 degrees and better
** than 20 arcmin (optical) or 30 arcmin (radio) at the horizon.
**
** Without refraction, the complementary functions eraAtco13 and
** eraAtoc13 are self-consistent to better than 1 microarcsecond
** all over the celestial sphere. With refraction included,
** consistency falls off at high zenith distances, but is still
** better than 0.05 arcsec at 85 degrees.
**
** 11) 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.
**
** Called:
** eraApco13 astrometry parameters, ICRS-observed
** eraAtoiq quick observed to CIRS
** eraAticq quick CIRS to ICRS
**
** Copyright (C) 2013-2015, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
int j;
eraASTROM astrom;
double eo, ri, di;
/* Star-independent astrometry parameters. */
j = eraApco13(utc1, utc2, dut1, elong, phi, hm, xp, yp,
phpa, tc, rh, wl, &astrom, &eo);
/* Abort if bad UTC. */
if ( j < 0 ) return j;
/* Transform observed to CIRS. */
eraAtoiq(type, ob1, ob2, &astrom, &ri, &di);
/* Transform CIRS to ICRS. */
eraAticq(ri, di, &astrom, rc, dc);
/* Return OK/warning status. */
return j;
/* Finished. */
}
void eraAtic13(double ri, double di, double date1, double date2,
double *rc, double *dc, double *eo)
/*
** - - - - - - - - - -
** e r a A t i c 1 3
** - - - - - - - - - -
**
** Transform star RA,Dec from geocentric CIRS to ICRS astrometric.
**
** Given:
** ri,di double CIRS geocentric RA,Dec (radians)
** date1 double TDB as a 2-part...
** date2 double ...Julian Date (Note 1)
**
** Returned:
** rc,dc double ICRS astrometric RA,Dec (radians)
** eo double equation of the origins (ERA-GST, Note 4)
**
** Notes:
**
** 1) The TDB date date1+date2 is a Julian Date, apportioned in any
** convenient way between the two arguments. For example,
** JD(TDB)=2450123.7 could be expressed in any of these ways, among
** others:
**
** date1 date2
**
** 2450123.7 0.0 (JD method)
** 2451545.0 -1421.3 (J2000 method)
** 2400000.5 50123.2 (MJD method)
** 2450123.5 0.2 (date & time method)
**
** The JD method is the most natural and convenient to use in cases
** where the loss of several decimal digits of resolution is
** acceptable. The J2000 method is best matched to the way the
** argument is handled internally and will deliver the optimum
** resolution. The MJD method and the date & time methods are both
** good compromises between resolution and convenience. For most
** applications of this function the choice will not be at all
** critical.
**
** TT can be used instead of TDB without any significant impact on
** accuracy.
**
** 2) Iterative techniques are used for the aberration and light
** deflection corrections so that the functions eraAtic13 (or
** eraAticq) and eraAtci13 (or eraAtciq) are accurate inverses;
** even at the edge of the Sun's disk the discrepancy is only about
** 1 nanoarcsecond.
**
** 3) The available accuracy is better than 1 milliarcsecond, limited
** mainly by the precession-nutation model that is used, namely
** IAU 2000A/2006. Very close to solar system bodies, additional
** errors of up to several milliarcseconds can occur because of
** unmodeled light deflection; however, the Sun's contribution is
** taken into account, to first order. The accuracy limitations of
** the ERFA function eraEpv00 (used to compute Earth position and
** velocity) can contribute aberration errors of up to
** 5 microarcseconds. Light deflection at the Sun's limb is
** uncertain at the 0.4 mas level.
**
** 4) Should the transformation to (equinox based) J2000.0 mean place
** be required rather than (CIO based) ICRS coordinates, subtract the
** equation of the origins from the returned right ascension:
** RA = RI - EO. (The eraAnp function can then be applied, as
** required, to keep the result in the conventional 0-2pi range.)
**
** Called:
** eraApci13 astrometry parameters, ICRS-CIRS, 2013
** eraAticq quick CIRS to ICRS astrometric
**
** Copyright (C) 2013-2016, NumFOCUS Foundation.
** Derived, with permission, from the SOFA library. See notes at end of file.
*/
{
/* Star-independent astrometry parameters */
eraASTROM astrom;
/* Star-independent astrometry parameters. */
eraApci13(date1, date2, &astrom, eo);
/* CIRS to ICRS astrometric. */
eraAticq(ri, di, &astrom, rc, dc);
/* Finished. */
}
