fw2xy¶

erfa.fw2xy(gamb, phib, psi, eps)[source]¶

CIP X,Y given Fukushima-Williams bias-precession-nutation angles.

Parameters:

gambdouble array
phibdouble array
psidouble array
epsdouble array

Returns:

xdouble array
ydouble array

Notes

Wraps ERFA function eraFw2xy. The ERFA documentation is:

- - - - - - - - -
 e r a F w 2 x y
- - - - - - - - -

CIP X,Y given Fukushima-Williams bias-precession-nutation angles.

Given:
   gamb     double    F-W angle gamma_bar (radians)
   phib     double    F-W angle phi_bar (radians)
   psi      double    F-W angle psi (radians)
   eps      double    F-W angle epsilon (radians)

Returned:
   x,y      double    CIP unit vector X,Y

Notes:

1) Naming the following points:

         e = J2000.0 ecliptic pole,
         p = GCRS pole
         E = ecliptic pole of date,
   and   P = CIP,

   the four Fukushima-Williams angles are as follows:

      gamb = gamma = epE
      phib = phi = pE
      psi = psi = pEP
      eps = epsilon = EP

2) The matrix representing the combined effects of frame bias,
   precession and nutation is:

      NxPxB = R_1(-epsA).R_3(-psi).R_1(phib).R_3(gamb)

   The returned values x,y are elements [2][0] and [2][1] of the
   matrix.  Near J2000.0, they are essentially angles in radians.

Called:
   eraFw2m      F-W angles to r-matrix
   eraBpn2xy    extract CIP X,Y coordinates from NPB matrix

Reference:

   Hilton, J. et al., 2006, Celest.Mech.Dyn.Astron. 94, 351

This revision:  2021 May 11

Copyright (C) 2013-2023, NumFOCUS Foundation.
Derived, with permission, from the SOFA library.  See notes at end of file.

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fw2xy¶