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Required Reading


   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.



      descr     respectively, file handle assigned to a SPK file and
                the descriptor for a segment within the file. Together
                they determine the ephemeris data from which the state
                of the body is to be computed.

                [1,1] = size(handle); int32 = class(handle)

                [5,1] = size(descr); double = class(descr)

      et        a scalar double precision time, in seconds past the
                epoch J2000 TDB.

                [1,1] = size(et); double = class(et)

   the call:

      [ref, state, center] = cspice_spkpvn( handle, descr, et)


      ref      the ID code of the reference frame relative to which the
               state returned by the routine is expressed.

               [1,1] = size(ref); int32 = class(ref)

      state    the array containing the position and velocity, at epoch
               'et', for the body covered by the specified segment. 'state'
               has six elements:  the first three contain the body's
               position; the last three contain the body's velocity. These
               vectors are expressed into the specified reference frame.
               Units are always km and km/sec.

               [6,1] = size(state); double = class(state)

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

               [1,1] = size(center); int32 = class(center)


   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.

   In the following code fragment, 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


         File name:

         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
            pck00010.tpc                  Planet orientation and
            naif0010.tls                  Leapseconds


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



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

      % Load meta-kernel.
      cspice_furnsh( META )

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

      et0 = cspice_str2et(timstr);

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

      [handle, descr, segid, found] = cspice_spksfs( body, et0);

      if ~found
         txt = sprintf( 'No SPK segment found for body %d at time %s', ...
                         body, timstr );
         error( txt )

      % Unpack the descriptor of the current segment.
      [dc, ic] = cspice_dafus( descr, ND, NI );

      frname = cspice_frmnam( ic(3) );

      fprintf( 'Body        = %d\n', ic(1) )
      fprintf( 'Center      = %d\n', ic(2) )
      fprintf( 'Frame       = %s\n', frname)
      fprintf( 'Data type   = %d\n', ic(4) )
      fprintf( 'Start ET    = %f\n', dc(1) )
      fprintf( 'Stop ET     = %f\n', dc(2) )
      fprintf( 'Segment ID  = %s\n\n', segid )

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

      for i=1:3

         et = et0 + ( 10. * (i-1) );

         % Convert `et' to a string for display.
         outstr = cspice_timout( et, TIMFMT );

         % Attempt to compute a state only if the segment's
         % coverage interval contains `et'.
         if ( et <= dc(2) )

            % This segment has data at `et'. Evaluate the
            % state of the target relative to its center
            % of motion.
            [ref_id, state, center] = cspice_spkpvn( handle, descr, et );

            %  Display the time and state.
            fprintf( '\n%s\n', outstr )
            fprintf( 'Position X (km):   %24.17f\n', state(1) )
            fprintf( 'Position Y (km):   %24.17f\n', state(2) )
            fprintf( 'Position Z (km):   %24.17f\n', state(3) )
            fprintf( 'Velocity X (km):   %24.17f\n', state(4) )
            fprintf( 'Velocity X (km):   %24.17f\n', state(5) )
            fprintf( 'Velocity X (km):   %24.17f\n', state(6) )


            txt = sprintf( 'No data found for body %d at time %s', ...
                         body, outstr );
            error( txt )



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

   MATLAB outputs:

      Body        = 5
      Center      = 0
      Frame       = J2000
      Data type   = 2
      Start ET    = -3169195200.000000
      Stop ET     = 1696852800.000000
      Segment ID  = DE-0421LE-0421

      2012 APR 27 00:00:00.000000 TDB
      Position X (km):   464528993.98216485977172852
      Position Y (km):   541513126.15685200691223145
      Position Z (km):   220785135.62462940812110901
      Velocity X (km):      -10.38685648307654930
      Velocity X (km):        7.95324700713742416
      Velocity X (km):        3.66185835431306517

      2012 APR 27 00:00:10.000000 TDB
      Position X (km):   464528890.11359262466430664
      Position Y (km):   541513205.68931341171264648
      Position Z (km):   220785172.24320945143699646
      Velocity X (km):      -10.38685796160419272
      Velocity X (km):        7.95324528430304944
      Velocity X (km):        3.66185765185608103

      2012 APR 27 00:00:20.000000 TDB
      Position X (km):   464528786.24500560760498047
      Position Y (km):   541513285.22175765037536621
      Position Z (km):   220785208.86178246140480042
      Velocity X (km):      -10.38685944013147910
      Velocity X (km):        7.95324356146845002
      Velocity X (km):        3.66185694939899253


   This routine finds the highest-priority segment, in any loaded
   SPK file, such that the segment provides data for the specified
   body and epoch.

Required Reading

   For important details concerning this module's function, please refer to
   the CSPICE routine spkpvn_c.



   -Mice Version 1.0.0, 30-OCT-2012, EDW (JPL)


   select spk file and segment

Wed Apr  5 18:00:35 2017