;+
; NAME:
;   oc_eph_et2fgh.pro
;
; PURPOSE:
;   returns [f,g,h,f',g',h'] for a eph at a given et
;
; DESCRIPTION:
;   returns [f,g,h,f',g',h'] for a eph at a given et
;   where h is toward a star, f is sky east, and g is sky north.
;
; CALLING SEQUENCE:
;   fgh = oc_eph_et2fgh(et,eph, star, method)
;
; INPUTS:
;   et - ephemeris time (seconds TDB after J2000)
;   eph - array of eph structures
; OPTIONAL INPUT PARAMETERS:
;
; KEYWORDS
;  method
;    'piececub' - piecewise cubic interpolation of the state
;    'naif'     - calls to naif routines, using eph.naif
; OUTPUTS:
;  If et is a scalar, return [ra, dec].
;
;  If et is an array, return [ radec_0, radec_1, ... ] where radec_i is for et[i]
;
;  If et is a scalar and the eph is an array of structures
;  then return [ radec_0, radec_1, ... ] where radec_i is for eph[i]
;  
;  If both et and the eph are arrays
;  then return [ radec_0, radec_1, ... ] where radec_i is for et[i], eph[i]
;  (if they are different lengths, then do up to the minimum)
; 
;  REVISON HISTORY:
;   2006 Jan 02 Leslie Young.  
;-

function oc_eph_et2fgh, et, eph, star, method = method

    net = n_elements(et)
    neph = n_elements(eph)
    
    if net eq 1 then begin
        state = oc_eph_et2state(et,eph, method=method)
        radec_star = oc_star_radec(et, star, dradec_star)
        fgh = rec6fgh6(state, radec_star, dradec_star)
        return, fgh
    endif
    
    fgh = dblarr(6,net)
    for i = 0, net - 1 do begin
        fgh[*,i] = oc_eph_et2fgh(et[i],eph, star, method = method)
    endfor
    return, state
end