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erfasrc/src/ltpb.c  view on Meta::CPAN

#include "erfa.h"

void eraLtpb(double epj, double rpb[3][3])
/*
**  - - - - - - - -
**   e r a L t p b
**  - - - - - - - -
**
**  Long-term precession matrix, including ICRS frame bias.
**
**  Given:
**     epj     double         Julian epoch (TT)
**
**  Returned:
**     rpb     double[3][3]   precession-bias matrix, J2000.0 to date
**
**  Notes:
**
**  1) The matrix is in the sense
**
**        P_date = rpb x P_ICRS,
**
**     where P_ICRS is a vector in the Geocentric Celestial Reference
**     System, and P_date is the vector with respect to the Celestial
**     Intermediate Reference System at that date but with nutation
**     neglected.
**
**  2) A first order frame bias formulation is used, of sub-
**     microarcsecond accuracy compared with a full 3D rotation.
**
**  3) The Vondrak et al. (2011, 2012) 400 millennia precession model
**     agrees with the IAU 2006 precession at J2000.0 and stays within
**     100 microarcseconds during the 20th and 21st centuries.  It is
**     accurate to a few arcseconds throughout the historical period,
**     worsening to a few tenths of a degree at the end of the
**     +/- 200,000 year time span.
**
**  References:
**
**    Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession
**    expressions, valid for long time intervals, Astron.Astrophys. 534,
**    A22
**
**    Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession
**    expressions, valid for long time intervals (Corrigendum),
**    Astron.Astrophys. 541, C1
**
**  Copyright (C) 2013-2020, NumFOCUS Foundation.
**  Derived, with permission, from the SOFA library.  See notes at end of file.
*/
{
/* Frame bias (IERS Conventions 2010, Eqs. 5.21 and 5.33) */
   const double dx = -0.016617 * ERFA_DAS2R,
                de = -0.0068192 * ERFA_DAS2R,
                dr = -0.0146 * ERFA_DAS2R;

   int i;
   double rp[3][3];


/* Precession matrix. */
   eraLtp(epj, rp);

/* Apply the bias. */
   for ( i = 0; i < 3; i++ ) {
      rpb[i][0] =  rp[i][0]    - rp[i][1]*dr + rp[i][2]*dx;
      rpb[i][1] =  rp[i][0]*dr + rp[i][1]    + rp[i][2]*de;
      rpb[i][2] = -rp[i][0]*dx - rp[i][1]*de + rp[i][2];
   }

}
/*----------------------------------------------------------------------
**  
**  
**  Copyright (C) 2013-2020, 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