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# c2tcio

erfa.c2tcio(rc2i, era, rpom)

  Assemble the celestial to terrestrial matrix from CIO-based components (the celestial-to-intermediate matrix, the Earth Rotation Angle and the polar motion matrix).

  Parameters
    rc2i double array
    era double array
    rpom double array
  Returns
    rc2t double array

  Notes

  Wraps ERFA function `eraC2tcio`. The ERFA documentation is:

      - - - - - - - - - -
       e r a C 2 t c i o
      - - - - - - - - - -

      Assemble the celestial to terrestrial matrix from CIO-based
      components (the celestial-to-intermediate matrix, the Earth Rotation
      Angle and the polar motion matrix).

      Given:
         rc2i     double[3][3]    celestial-to-intermediate matrix
         era      double          Earth rotation angle (radians)
         rpom     double[3][3]    polar-motion matrix

      Returned:
         rc2t     double[3][3]    celestial-to-terrestrial matrix

      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
         intermediate frame, the Earth rotation angle and the polar motion
         matrix.  One use of the present function is when generating a
         series of celestial-to-terrestrial matrices where only the Earth
         Rotation Angle 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(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).

      Called:
         eraCr        copy r-matrix
         eraRz        rotate around Z-axis
         eraRxr       product of two r-matrices

      Reference:

         McCarthy, D. D., Petit, G. (eds.), 2004, IERS Conventions (2003),
         IERS Technical Note No. 32, BKG

      This revision:  2021 May 11

      Copyright (C) 2013-2021, NumFOCUS Foundation.
      Derived, with permission, from the SOFA library.  See notes at end of file.