;+
; NAME:
;   oc_naifstate.pro
;
; PURPOSE:
;   returns a 6-element state (or a 6 x n matrix)
;
; DESCRIPTION:
;   Calculates the state using the NAIF ICY routines.
;
; CALLING SEQUENCE:
;   state = oc_naifstate(et,targ,$
;      obs=obs,abcorr=abcorr,frame=frame,lonlatalt=lonlatalt)
;
; INPUTS:
;   et - the ET at which you want to know the coordinates (may be an
;        array).  Units are seconds of TDB (barycentric dynamical
;        time) after J2000.
;   targ = target code
;
; KEYWORDS
;   obs - the keyword argument that indicates the observer location, 
;         default to Earth center (399).
;   abcorr  - aberation correction.  Default 'LT'
;   frame   - frame of state, ra, dec.  Default 'J2000'
;   lonlatalt - lon, lat, altitude for topocentric
;               ephemerides. Default geocentric
; OUTPUTS:
;   ltime - optional output of light-travel time
;   
;   If et is a double, then return state = [x,y,z,x',y',z'] in 
;   km and km/s.
;   If et is an array, return statearr = [ [state0], [state1], ...]
;   so single states are accessed by statearr[*,i]
;
; RESTRICTIONS
;   For geocentric observations, ltime and position can be off by
;    Re/c = 21 ms.
; 
;  REVISON HISTORY:
;   2006 Jan 02 Leslie Young.  Based on single_eph
;   2006 May 11 LAY Added ltime
;   2009 Oct 21 LAY Change i in loop to long
;-

function oc_naifstate, et,targ,$
                       obs=obs,abcorr=abcorr,frame=frame,lonlatalt=lonlatalt, ltime=ltime

    naifinit

;    if not keyword_set(obs) then obs = 399 ; Earth
    if n_elements(obs) eq 0 then obs = 399 ; Earth
    if not keyword_set(abcorr) then abcorr = 'LT' ; light-time only
    if not keyword_set(frame) then frame = 'J2000' ; 

    n = n_elements(et)
    statearr = dblarr(6,n)
    ltime = dblarr(n)
    for i = 0L, n-1 do begin
        e = et[i]
        CSPICE_SPKEZ, targ, e, frame, abcorr, obs, $
          stateTarget, ltime1
        if keyword_set(lonlatalt) then begin
            stateTarget = stateTarget - oc_lla2xyz(lonlatalt,e)
        endif 
        statearr[*,i] = stateTarget
        ltime[i] = ltime1
    end

    if n eq 1 then begin
        if isarray(et) then begin
            return, reform(statearr,6,1)
        endif else begin
            ltime = ltime[0]
            return, reform(statearr[*,0], 6)
        endelse
    endif else begin
        return, statearr
    endelse

end