era.pom00.md

eraPom00

rpom = ERFA.pom00(xp, yp, sp)

Form the matrix of polar motion for a given date, IAU 2000.

Given:

   xp,yp    double    coordinates of the pole (radians, Note 1)
   sp       double    the TIO locator s' (radians, Note 2)

Returned:

   rpom     double[3][3]   polar-motion matrix (Note 3)

Notes:

1. The arguments xp and yp are the coordinates (in radians) of the Celestial Intermediate Pole with respect to the International Terrestrial Reference System (see IERS Conventions 2003), measured along the meridians 0 and 90 deg west respectively.

2. The argument sp is the TIO locator s', in radians, which positions the Terrestrial Intermediate Origin on the equator. It is obtained from polar motion observations by numerical integration, and so is in essence unpredictable. However, it is dominated by a secular drift of about 47 microarcseconds per century, and so can be taken into account by using s' = -47*t, where t is centuries since J2000.0. The function eraSp00 implements this approximation.

3. The matrix operates in the sense V(TRS) = rpom * V(CIP), meaning that it is the final rotation when computing the pointing direction to a celestial source.

Called:

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