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fw2xy

sofars::pnp

Function fw2xy 

Source 
pub fn fw2xy(gamb: f64, phib: f64, psi: f64, eps: f64) -> (f64, f64)
Expand description

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

This function is part of the International Astronomical Union’s SOFA (Standards of Fundamental Astronomy) software collection.

Status: support function.

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 (function value): (x, y) (f64, f64) 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: iauFw2m F-W angles to r-matrix iauBpn2xy extract CIP X,Y coordinates from NPB matrix

Reference:

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