c2i06a.c

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#include "erfa.h"

void eraC2i06a(double date1, double date2, double rc2i[3][3])
/*
**  - - - - - - - - - -
**   e r a C 2 i 0 6 a
**  - - - - - - - - - -
**
**  Form the celestial-to-intermediate matrix for a given date using the
**  IAU 2006 precession and IAU 2000A nutation models.
**
**  Given:
**     date1,date2 double       TT as a 2-part Julian Date (Note 1)
**
**  Returned:
**     rc2i        double[3][3] celestial-to-intermediate matrix (Note 2)
**
**  Notes:
**
**  1) The TT date date1+date2 is a Julian Date, apportioned in any
**     convenient way between the two arguments.  For example,
**     JD(TT)=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.
**
**  2) The matrix rc2i is the first stage in the transformation 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), ERA is the Earth
**     Rotation Angle and RPOM is the polar motion matrix.
**
**  Called:
**     eraPnm06a    classical NPB matrix, IAU 2006/2000A
**     eraBpn2xy    extract CIP X,Y coordinates from NPB matrix
**     eraS06       the CIO locator s, given X,Y, IAU 2006
**     eraC2ixys    celestial-to-intermediate matrix, given X,Y and s
**
**  References:
**
**     McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
**     IERS Technical Note No. 32, BKG
**
**  Copyright (C) 2013-2015, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
   double rbpn[3][3], x, y, s;

/* Obtain the celestial-to-true matrix (IAU 2006/2000A). */
   eraPnm06a(date1, date2, rbpn);

/* Extract the X,Y coordinates. */
   eraBpn2xy(rbpn, &x, &y);

/* Obtain the CIO locator. */
   s = eraS06(date1, date2, x, y);

/* Form the celestial-to-intermediate matrix. */
   eraC2ixys(x, y, s, rc2i);

   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
**  
**  Redistribution and use in source and binary forms, with or without
**  modification, are permitted provided that the following conditions
**  are met:
**  
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**    notice, this list of conditions and the following disclaimer.
**  
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**  
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*/