era.c2ixys.md

eraC2ixys

rc2i = ERFA.c2ixys(x, y, s)

Form the celestial to intermediate-frame-of-date matrix given the CIP X,Y and the CIO locator s.

Given:

   x,y      double         Celestial Intermediate Pole (Note 1)
   s        double         the CIO locator s (Note 2)

Returned:

   rc2i     double[3][3]   celestial-to-intermediate matrix (Note 3)

Notes:

1. The Celestial Intermediate Pole coordinates are the x,y components of the unit vector in the Geocentric Celestial Reference System.

2. The CIO locator s (in radians) positions the Celestial Intermediate Origin on the equator of the CIP.

3. 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:

   eraIr        initialize r-matrix to identity
   eraRz        rotate around Z-axis
   eraRy        rotate around Y-axis

Reference:

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

This revision: 2021 May 11

Copyright (C) 2013-2021, NumFOCUS Foundation. Derived, with permission, from the SOFA library.