c2t00a.c

#include "erfa.h"

void eraC2t00a(double tta, double ttb, double uta, double utb,
               double xp, double yp, double rc2t[3][3])
/*
**  - - - - - - - - - -
**   e r a C 2 t 0 0 a
**  - - - - - - - - - -
**
**  Form the celestial to terrestrial matrix given the date, the UT1 and
**  the polar motion, using the IAU 2000A precession-nutation model.
**
**  Given:
**     tta,ttb  double         TT as a 2-part Julian Date (Note 1)
**     uta,utb  double         UT1 as a 2-part Julian Date (Note 1)
**     xp,yp    double         CIP coordinates (radians, Note 2)
**
**  Returned:
**     rc2t     double[3][3]   celestial-to-terrestrial matrix (Note 3)
**
**  Notes:
**
**  1) The TT and UT1 dates tta+ttb and uta+utb are Julian Dates,
**     apportioned in any convenient way between the arguments uta and
**     utb.  For example, JD(UT1)=2450123.7 could be expressed in any of
**     these ways, among others:
**
**             uta            utb
**
**         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 and MJD methods are good compromises
**     between resolution and convenience.  In the case of uta,utb, the
**     date & time method is best matched to the Earth rotation angle
**     algorithm used:  maximum precision is delivered when the uta
**     argument is for 0hrs UT1 on the day in question and the utb
**     argument lies in the range 0 to 1, or vice versa.
**
**  2) The arguments xp and yp 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.
**
**  3) The matrix rc2t transforms from celestial to terrestrial
**     coordinates:
**
**        [TRS] = RPOM * R_3(ERA) * RC2I * [CRS]
**
**              = rc2t * [CRS]
**
**     where [CRS] is a vector in the Geocentric Celestial Reference
**     System and [TRS] is a vector in the International Terrestrial
**     Reference System (see IERS Conventions 2003), RC2I is the
**     celestial-to-intermediate matrix, ERA is the Earth rotation
**     angle and RPOM is the polar motion matrix.
**
**  4) A faster, but slightly less accurate, result (about 1 mas) can
**     be obtained by using instead the eraC2t00b function.
**
**  Called:
**     eraC2i00a    celestial-to-intermediate matrix, IAU 2000A
**     eraEra00     Earth rotation angle, IAU 2000
**     eraSp00      the TIO locator s', IERS 2000
**     eraPom00     polar motion matrix
**     eraC2tcio    form CIO-based celestial-to-terrestrial matrix
**
**  Reference:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**  This revision:  2021 May 11
**
**  Copyright (C) 2013-2023, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double rc2i[3][3], era, sp, rpom[3][3];


/* Form the celestial-to-intermediate matrix for this TT (IAU 2000A). */
   eraC2i00a(tta, ttb, rc2i );

/* Predict the Earth rotation angle for this UT1. */
   era = eraEra00(uta, utb);

/* Estimate s'. */
   sp = eraSp00(tta, ttb);

/* Form the polar motion matrix. */
   eraPom00(xp, yp, sp, rpom);

/* Combine to form the celestial-to-terrestrial matrix. */
   eraC2tcio(rc2i, era, rpom, rc2t);

/* Finished. */

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2023, NumFOCUS Foundation.
**  All rights reserved.
**  
**  This library is derived, with permission, from the International
**  Astronomical Union's "Standards of Fundamental Astronomy" library,
**  available from http://www.iausofa.org.
**  
**  The ERFA version is intended to retain identical functionality to
**  the SOFA library, but made distinct through different function and
**  file names, as set out in the SOFA license conditions.  The SOFA
**  original has a role as a reference standard for the IAU and IERS,
**  and consequently redistribution is permitted only in its unaltered
**  state.  The ERFA version is not subject to this restriction and
**  therefore can be included in distributions which do not support the
**  concept of "read only" software.
**  
**  Although the intent is to replicate the SOFA API (other than
**  replacement of prefix names) and results (with the exception of
**  bugs;  any that are discovered will be fixed), SOFA is not
**  responsible for any errors found in this version of the library.
**  
**  If you wish to acknowledge the SOFA heritage, please acknowledge
**  that you are using a library derived from SOFA, rather than SOFA
**  itself.
**  
**  
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