C2TEQX Subroutine

public subroutine C2TEQX(rbpn, gst, rpom, rc2t)

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).

Status: support routine.

Notes

1. This routine 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 routine 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).

Reference

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

History

• IAU SOFA revision: 2013 August 24

Arguments

    subroutine C2TEQX ( rbpn, gst, rpom, rc2t )

    implicit none

    real(wp),dimension(3,3),intent(in) :: rbpn !! celestial-to-true matrix
    real(wp),intent(in) :: gst !! Greenwich (apparent) Sidereal Time (radians)
    real(wp),dimension(3,3),intent(in) :: rpom !! polar-motion matrix
    real(wp),dimension(3,3),intent(out) :: rc2t !! celestial-to-terrestrial matrix (Note 2)

    real(wp) :: r(3,3)

    !  Construct the matrix.
    call CR ( rbpn, r )
    call RZ ( gst, r )
    call RXR ( rpom, r, rc2t )

    end subroutine C2TEQX