;+
;       NAME:
;               oc_ephicy_arclen.Pro
;
;       PURPOSE:
;		Returns a structure with the following information:
;                 {et, ra, dec, radot, decdot, ephinfo} where ephinfo
;                 contains the observer range and observer range rate.
;
;	DESCRIPTION:
;              Calculates the ra, dec, radot, decdot, observer range
;              and range rate using the NAIF ICY routines.
;
;       CALLING SEQUENCE:
;               oc_ephicy_arclen, target, observer, utcStrStart, utcStrEnd,
;               arclen, eph
;
;       INPUTS:
;              target - the target for the ephemeris, i.e. "Pluto"
;              observer - the observer location, i.e. "Earth"
;              utcStrStart - the UTC string of the start time,
;                            i.e. "January 11, 2006 00:00:00"
;              utcStrEnd - the UTC string of the end time
;              arclen - the increment in sky-plane distance traveled
;                       by the target, radians
;       OUTPUTS:
;              eph - a structure with the following elements
;              eph.ra - the Pluto RA in radians
;              eph.dec - the Pluto Dec in radians
;              eph.radot - the RA rate in radians/s
;                          (d(ra)*cos(dec)/dt)
;              eph.decdot -- the Dec rate in radians/s
;              eph.ephinfo - the observer range (in km)
;                                          and range rate (km/s).
;
;
;       REVISON HISTORY:
;       17-January-2005 CBO SwRI
;-

pro	oc_ephicy_arclen, target, observer, utcStrStart, utcStrEnd, arclen, eph

       naifinit

; Generate the time list
       CSPICE_STR2ET, utcStrStart, et0
       CSPICE_STR2ET, utcStrEnd, et1

       count = 0L
      
       single_eph, target, et0, eph1, observer=observer

       tmp = eph1

       time = et0
       WHILE time LT et1 DO BEGIN
           
           dt = arclen/SQRT(eph1.radot^2 + eph1.decdot^2)
           time = time + dt
           count = count + 1
           single_eph, target, time, eph1, observer=observer
           tmp=[tmp,eph1]

       ENDWHILE

      eph = tmp

 END

;+