c2teqx.c

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#include "erfa.h"

void eraC2teqx(double rbpn[3][3], double gst, double rpom[3][3],
               double rc2t[3][3])
/*
**  - - - - - - - - - -
**   e r a C 2 t e q x
**  - - - - - - - - - -
**
**  Assemble the celestial to terrestrial matrix from equinox-based
**  components (the celestial-to-true matrix, the Greenwich Apparent
**  Sidereal Time and the polar motion matrix).
**
**  Given:
**     rbpn   double[3][3]  celestial-to-true matrix
**     gst    double        Greenwich (apparent) Sidereal Time (radians)
**     rpom   double[3][3]  polar-motion matrix
**
**  Returned:
**     rc2t   double[3][3]  celestial-to-terrestrial matrix (Note 2)
**
**  Notes:
**
**  1) This function constructs the rotation matrix that transforms
**     vectors in the celestial system into vectors in the terrestrial
**     system.  It does so starting from precomputed components, namely
**     the matrix which rotates from celestial coordinates to the
**     true equator and equinox of date, the Greenwich Apparent Sidereal
**     Time and the polar motion matrix.  One use of the present function
**     is when generating a series of celestial-to-terrestrial matrices
**     where only the Sidereal Time changes, avoiding the considerable
**     overhead of recomputing the precession-nutation more often than
**     necessary to achieve given accuracy objectives.
**
**  2) The relationship between the arguments is as follows:
**
**        [TRS] = rpom * R_3(gst) * rbpn * [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).
**
**  Called:
**     eraCr        copy r-matrix
**     eraRz        rotate around Z-axis
**     eraRxr       product of two r-matrices
**
**  Reference:
**
**     McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG (2004)
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double r[3][3];

/* Construct the matrix. */
   eraCr(rbpn, r);
   eraRz(gst, r);
   eraRxr(rpom, r, rc2t);

   return;

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2015, 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.
**  
**  
**  TERMS AND CONDITIONS
**  
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**  modification, are permitted provided that the following conditions
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**  
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