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cspice_spkpvn

Table of contents
Abstract
I/O
Parameters
Examples
Particulars
Exceptions
Files
Restrictions
Required_Reading
Literature_References
Author_and_Institution
Version
Index_Entries


Abstract


   CSPICE_SPKPVN returns, for a specified SPK segment and time, the state
   (position and velocity) of the segment's target body relative to its
   center of motion.

I/O


   Given:

      handle,
      descr    the file handle assigned to an SPK file, and the descriptor for
               a segment within the file.

               help, handle
                  LONG = Scalar
               help, descr
                  DOUBLE = Array[5]

               Together they determine the ephemeris data from which the state
               of the body is to be computed.

      et       the epoch (ephemeris time) at which the state is to be computed.

               help, et
                  DOUBLE = Scalar

   the call:

      cspice_spkpvn, handle, descr, et, ref, state, center

   returns:

      ref      the id-code of the reference frame to which the vectors returned
               by the routine belong.

               help, ref
                  LONG = Scalar

      state    a 6-dimensional vector that contains the position and velocity,
               at epoch `et', for whatever body is covered by the specified
               segment.

               help, state
                  DOUBLE = Array[6]

               `state' has six elements: the first three contain the body's
               position; the last three contain the body's velocity. These
               vectors are rotated into the specified reference frame, the
               origin of which is located at the center of motion for the body
               (see `center', below). Units are always km and km/sec.

      center   the integer ID code of the center of motion for the state.

               help, center
                  LONG = Scalar

Parameters


   None.

Examples


   Any numerical results shown for this example may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

   1) In the following code example, an SPK file is searched for
      a segment containing ephemeris data for the Jupiter system
      barycenter at a particular epoch. Using this segment,
      states of the Jupiter system barycenter relative to the
      solar system barycenter are evaluated at a sequence of times.

      This method of state computation minimizes the number of
      segment searches required to obtain requested data, but
      it bypasses the SPK subsystem's state chaining mechanism.


      Use the meta-kernel shown below to load the required SPICE
      kernels.


         KPL/MK

         File name: spkpvn_ex1.tm

         This meta-kernel is intended to support operation of SPICE
         example programs. The kernels shown here should not be
         assumed to contain adequate or correct versions of data
         required by SPICE-based user applications.

         In order for an application to use this meta-kernel, the
         kernels referenced here must be present in the user's
         current working directory.

         The names and contents of the kernels referenced
         by this meta-kernel are as follows:

            File name                     Contents
            ---------                     --------
            de421.bsp                     Planetary ephemeris
            naif0010.tls                  Leapseconds

         \begindata

            KERNELS_TO_LOAD = ( 'de421.bsp',
                                'naif0010.tls'  )

         \begintext

         End of meta-kernel


      Example code begins here.


      PRO spkpvn_ex1

         ;;
         ;; Local constants
         ;;
         META   =  'spkpvn_ex1.tm'
         ND     =  2
         NI     =  6
         TIMFMT =  'YYYY MON DD HR:MN:SC.######::TDB TDB'
         TIMLEN =  41


         ;;
         ;; Load meta-kernel.
         ;;
         cspice_furnsh, META

         ;;
         ;; Convert starting time to seconds past J2000 TDB.
         ;;
         timstr = '2012 APR 27 00:00:00.000 TDB'

         cspice_str2et, timstr, et0

         ;;
         ;; Find a loaded segment for the Jupiter barycenter
         ;; that covers 'et0'.
         ;;
         body = 5;

         cspice_spksfs, body,   et0,               $
                        handle, descr, segid,  found

         if ( ~found ) then begin
            cspice_kclear
            print, 'Body : ', body
            print, 'Time : ', timstr
            print, 'No SPK segment found for the body at time.'
            return
         endif

         ;;
         ;; Unpack the descriptor of the current segment.
         ;;
         cspice_dafus, descr, ND, NI, dc, ic

         cspice_frmnam, ic[2], frname

         print, format='(A, I10)',   'Body        = ',ic[0]
         print, format='(A, I10)',   'Center      = ',ic[1]
         print, format='(A, A)',     'Frame       = ',frname
         print, format='(A, I10)',   'Data type   = ', ic[3]
         print, format='(A, e16.8)', 'Start ET    = ',dc[0]
         print, format='(A, e16.8)', 'Stop ET     = ',dc[1]
         print, format='(A, A)',     'Segment ID = ',segid
         print


         ;;
         ;; Evaluate states at 10-second steps, starting at 'et0'
         ;; and continuing for 20 seconds.
         ;;

         for i=0, 2 do begin

            et = et0 + ( 10.D * i )

            ;;
            ;; Convert 'et' to a string for display.
            ;;
            cspice_timout, et, TIMFMT, TIMLEN, outstr

            ;;
            ;; Attempt to compute a state only if the segment's
            ;; coverage interval contains 'et'.
            ;;
            if ( et le dc[1] ) then begin

               ;;
               ;; This segment has data at 'et'. Evaluate the
               ;; state of the target relative to its center
               ;; of motion.
               ;;
               cspice_spkpvn, handle, descr, et, ref_id, state, center

               ;;
               ;;  Display the time and state.
               ;;
               print, outstr
               print, format='(A, e24.17)', 'Position X (km):   ',state[0]
               print, format='(A, e24.17)', 'Position Y (km):   ',state[1]
               print, format='(A, e24.17)', 'Position Z (km):   ',state[2]
               print, format='(A, e24.17)', 'Velocity X (km/s): ',state[3]
               print, format='(A, e24.17)', 'Velocity Y (km/s): ',state[4]
               print, format='(A, e24.17)', 'Velocity Z (km/s): ',state[5]
               print

            endif else begin

               print, 'Body : ', body
               print, 'Time : ', outstr
               print, 'No data for body found at time'

               cspice_kclear
               return

            endelse

         endfor

         ;;
         ;; It's always good form to unload kernels after use,
         ;; particularly in IDL due to data persistence.
         ;;
         cspice_kclear

      END


      When this program was executed on a Mac/Intel/IDL8.x/64-bit
      platform, the output was:


      Body        =          5
      Center      =          0
      Frame       = J2000
      Data type   =          2
      Start ET    =  -3.16919520e+09
      Stop ET     =   1.69685280e+09
      Segment ID = DE-0421LE-0421

      2012 APR 27 00:00:00.000000 TDB
      Position X (km):    4.64528993982164860e+08
      Position Y (km):    5.41513126156852007e+08
      Position Z (km):    2.20785135624629408e+08
      Velocity X (km/s): -1.03868564830765493e+01
      Velocity Y (km/s):  7.95324700713742416e+00
      Velocity Z (km/s):  3.66185835431306517e+00

      2012 APR 27 00:00:10.000000 TDB
      Position X (km):    4.64528890113592625e+08
      Position Y (km):    5.41513205689313412e+08
      Position Z (km):    2.20785172243209451e+08
      Velocity X (km/s): -1.03868579616041927e+01
      Velocity Y (km/s):  7.95324528430304944e+00
      Velocity Z (km/s):  3.66185765185608103e+00

      2012 APR 27 00:00:20.000000 TDB
      Position X (km):    4.64528786245005608e+08
      Position Y (km):    5.41513285221757650e+08
      Position Z (km):    2.20785208861782461e+08
      Velocity X (km/s): -1.03868594401314791e+01
      Velocity Y (km/s):  7.95324356146845002e+00
      Velocity Z (km/s):  3.66185694939899253e+00


Particulars


   For most user applications, the high-level SPK APIs

      cspice_spkezr
      cspice_spkez
      cspice_spkpos
      cspice_spkezp

   should be used instead of this routine.

   The f2c'd routine spkpvn_ called by cspice_spkpvn is the most basic of
   the SPK readers, the reader upon which spkezr_c and spkgeo_c, etc.
   are built. cspice_spkpvn normally should not be called directly except in
   cases where some optimization is required. (That is, where the
   calling program has prior knowledge of the center-barycenter shifts
   to be performed, or a non-standard method of determining the files
   and segments to be used when computing states.)

   This is the only reader that makes distinctions between the
   various segment types in the SPK format. The complete list
   of types currently supported is shown below.

      Type   Description
      ----   -------------------------
         1   Modified Difference Array
         2   Chebyshev (P)
         3   Chebyshev (P,V)
         5   Two body propagation between discrete states
         8   Lagrange interpolation, equally spaced discrete states
         9   Lagrange interpolation, unequally spaced discrete states
        12   Hermite interpolation, equally spaced discrete states
        13   Hermite interpolation, unequally spaced discrete states
        14   Chebyshev Unequally spaced
        15   Precessing Ellipse
        17   Equinoctial Elements
        18   ESOC/DDID Hermite/Lagrange Interpolation
        19   ESOC/DDID Piecewise Interpolation
        21   Extended Modified Difference Array

      The maximum record lengths for each data type currently
      supported are as follows:

                Data type       Maximum record length
                ---------       ---------------------
                    1                    71
                    2                    87
                    3                   171
                    5                    15
                    8                   171
                    9                   197
                   12                    87
                   13                    99
                   14                 Variable
                   15                    16
                   17                    12
                   18                   198
                   19                   198
                   21                    96

Exceptions


   1)  If the segment type is not supported by the current
       version of cspice_spkpvn, the error SPICE(SPKTYPENOTSUPP)
       is signaled by a routine in the call tree of this routine.

   2)  If any of the input arguments, `handle', `descr' or `et', is
       undefined, an error is signaled by the IDL error handling
       system.

   3)  If any of the input arguments, `handle', `descr' or `et', is
       not of the expected type, or it does not have the expected
       dimensions and size, an error is signaled by the Icy
       interface.

   4)  If any of the output arguments, `ref', `state' or `center', is
       not a named variable, an error is signaled by the Icy
       interface.

Files


   See argument `handle'.

Restrictions


   None.

Required_Reading


   SPK.REQ

Literature_References


   None.

Author_and_Institution


   J. Diaz del Rio     (ODC Space)
   E.D. Wright         (JPL)

Version


   -Icy Version 1.0.1, 09-AUG-2021 (JDR)

       Edited header to comply with NAIF standard.

       Added -Parameters, -Exceptions, -Files, -Restrictions,
       -Literature_References and -Author_and_Institution sections.

       Removed reference to the routine's corresponding CSPICE header from
       -Abstract section.

       Added arguments' type and size information in the -I/O section.

   -Icy Version 1.0.0, 24-OCT-2012 (EDW)

Index_Entries


   position and velocity from ephemeris
   SPK file position and velocity



Fri Dec 31 18:43:07 2021