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Index Page spkw17_c
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Procedure Abstract Required_Reading Keywords Brief_I/O Detailed_Input | Detailed_Output Parameters Exceptions Files Particulars Examples | Restrictions Literature_References Author_and_Institution Version Index_Entries
#### Procedure
       spkw17_c ( SPK, write a type 17 segment )

       void spkw17_c ( SpiceInt           handle,
                       SpiceInt           body,
                       SpiceInt           center,
                       ConstSpiceChar   * frame,
                       SpiceDouble        first,
                       SpiceDouble        last,
                       ConstSpiceChar   * segid,
                       SpiceDouble        epoch,
                       ConstSpiceDouble   eqel   [9],
                       SpiceDouble        rapol,
                       SpiceDouble        decpol      )
#### Abstract
       Write an SPK segment of type 17 given a type 17 data record.
#### Required_Reading
       SPK
#### Keywords
       EPHEMERIS
#### Brief_I/O
       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       handle     I   Handle of an SPK file open for writing.
       body       I   Body code for ephemeris object.
       center     I   Body code for the center of motion of the body.
       frame      I   The reference frame of the states.
       first      I   First valid time for which states can be computed.
       last       I   Last valid time for which states can be computed.
       segid      I   Segment identifier.
       epoch      I   Epoch of elements in seconds past J2000.
       eqel       I   Array of equinoctial elements.
       rapol      I   Right Ascension of the reference plane's pole.
       decpol     I   Declination of the reference plane's pole.
#### Detailed_Input
       handle      is the file handle of an SPK file that has been
                   opened for writing.

       body        is the NAIF ID for the body whose states are
                   to be recorded in the SPK file.

       center      is the NAIF ID for the center of motion associated
                   with `body'.

       frame       is the reference frame that states are referenced to,
                   for example "J2000".

       first,
       last        are the bounds on the ephemeris times, expressed as
                   seconds past J2000.

       segid       is the segment identifier. An SPK segment identifier
                   may contain up to 40 characters.

       epoch       is the epoch of equinoctial elements in seconds
                   past the J2000 epoch.

       eqel        is an array of 9 double precision numbers that
                   are the equinoctial elements for some orbit relative
                   to the equatorial frame of a central body.

                      Note: The Z-axis of the equatorial frame is the
                      direction of the pole of the central body relative
                      to `frame'. The X-axis is given by the cross product of
                      the Z-axis of `frame' with the direction of the pole of
                      the central body. The Y-axis completes a right handed
                      frame.

                   The specific arrangement of the elements is spelled
                   out below. The following terms are used in the
                   discussion of elements of `eqel':

                      inc  --- inclination of the orbit
                      argp --- argument of periapse
                      node --- longitude of the ascending node
                      e    --- eccentricity of the orbit
                      m0   --- mean anomaly

                   eqel[0]   is the semi-major axis (A) of the orbit in km.

                   eqel[1]   is the value of H at the specified epoch:

                                H =  e * sin( argp + node )

                   eqel[2]   is the value of K at the specified epoch:

                                K =  e * cos( argp + node )

                   eqel[3]   is the mean longitude at the epoch of the
                             elements measured in radians:

                                ( m0 + argp + node )

                   eqel[4]   is the value of P at the specified epoch:

                                P =  tan( inc/1 ) * sin( node )

                   eqel[5]   is the value of Q at the specified epoch:

                                Q =  tan( inc/1 ) * cos( node );

                   eqel[6]   is the rate of the longitude of periapse
                             at the epoch of the elements.

                                ( dargp/dt + dnode/dt )

                             This rate is assumed to hold for all time. The
                             rate is measured in radians per second.

                   eqel[7]   is the derivative of the mean longitude:

                                ( dm0/dt + dargp/dt + dnode/dt )

                             This rate is assumed to be constant and is
                             measured in radians/second.

                   eqel[8]   is the rate of the longitude of the ascending
                             node:

                                ( dnode/dt )

                             This rate is measured in radians per second.

       rapol       is the Right Ascension of the pole of the reference
                   plane relative to `frame' measured in radians.

       decpol      is the declination of the pole of the reference plane
                   relative to `frame' measured in radians.
#### Detailed_Output
       None.

       The routine writes an SPK type 17 segment to the file attached to
       `handle'.
#### Parameters
       None.
#### Exceptions
       1)  If the semi-major axis is less than or equal to zero, the
           error SPICE(BADSEMIAXIS) is signaled by a routine in the call
           tree of this routine.

       2)  If the eccentricity of the orbit corresponding to the values
           of H and K ( eqel[1] and eqel[2] ) is greater than 0.9, the
           error SPICE(ECCOUTOFRANGE) is signaled by a routine in the
           call tree of this routine.

       3)  If the segment identifier has more than 40 non-blank
           characters, the error SPICE(SEGIDTOOLONG) is signaled by a
           routine in the call tree of this routine.

       4)  If the segment identifier contains non-printing characters,
           the error SPICE(NONPRINTABLECHARS) is signaled by a routine in
           the call tree of this routine.

       5)  If there are inconsistencies in the `body', `center', `frame' or
           `first' and `last' times, an error is signaled by a routine in
           the call tree of this routine.

       6)  If any of the `frame' or `segid' input string pointers is
           null, the error SPICE(NULLPOINTER) is signaled.

       7)  If any of the `frame' or `segid' input strings has zero
           length, the error SPICE(EMPTYSTRING) is signaled.
#### Files
       A new type 17 SPK segment is written to the SPK file attached
       to `handle'.
#### Particulars
       This routine writes an SPK type 17 data segment to the open SPK
       file according to the format described in the type 17 section of
       the SPK Required Reading. The SPK file must have been opened with
       write access.
#### Examples
       The numerical results shown for this example may differ across
       platforms. The results depend on the SPICE kernels used as
       input, the compiler and supporting libraries, and the machine
       specific arithmetic implementation.

       1) Suppose that at a given time you have the classical elements
          of Daphnis relative to the equatorial frame of Saturn. These
          can be converted to equinoctial elements and stored in an SPK
          file as a type 17 segment so that Daphnis can be used within
          the SPK subsystem of the SPICE system.

          The example code shown below creates an SPK type 17 kernel
          with a single segment using such data.

          Example code begins here.

          /.
             Program spkw17_ex1
          ./
          #include <math.h>
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Local parameters.
             ./
             #define SPK17        "spkw17_ex1.bsp"

             /.
             The SPK type 17 segment will contain data for Daphnis
             (ID 635) with respect to Saturn (ID 699) in the J2000
             reference frame.
             ./
             #define BODY         635
             #define CENTER       699
             #define FRMNAM       "J2000"

             /.
             This is the list of parameters used to represent the
             classical elements:

                Variable     Meaning
                --------     ---------------------------------------
                A            Semi-major axis in km.
                ECC          Eccentricity of orbit.
                INC          Inclination of orbit.
                NODE         Longitude of the ascending node at
                             epoch.
                OMEGA        Argument of periapse at epoch.
                M            Mean anomaly at epoch.
                DMDT         Mean anomaly rate in radians/second.
                DNODE        Rate of change of longitude of
                             ascending node in radians/second.
                DOMEGA       Rate of change of argument of periapse
                             in radians/second.
                EPOCH        The epoch of the elements in seconds
                             past the J2000 epoch.
             ./
             #define A            1.36505608e+05
             #define ECC          -2.105898062e-05
             #define INC          -3.489710429e-05
             #define NODE         -3.349237456e-02
             #define OMEGA        1.52080206722
             #define M            1.21177109734
             #define DMDT         1.218114014e-04
             #define DNODE        -5.96845468e-07
             #define DOMEGA       1.196601093e-06
             #define EPOCH        0.0

             /.
             In addition, the spkw17_c routine requires the Right
             Ascension and Declination of the pole of the
             reference plane relative to the J2000 frame, in radians.
             ./
             #define RAPOL        7.08332284e-01
             #define DECPOL       1.45800286

             /.
             Local variables.
             ./
             SpiceChar          * ifname;
             SpiceChar          * segid;

             SpiceDouble          eqel   [9];
             SpiceDouble          first;
             SpiceDouble          last;

             SpiceInt             handle;
             SpiceInt             ncomch;

             /.
             Set the start and end times of interval covered by
             segment.
             ./
             first  =  504878400.0;
             last   = 1578657600.0;

             /.
             `ncomch' is the number of characters to reserve for the
             kernel's comment area. This example doesn't write
             comments, so set to zero.
             ./
             ncomch = 0;

             /.
             Internal file name and segment ID.
             ./
             ifname = "Test for type 17 SPK internal file name";
             segid  = "SPK type 17 test segment";

             /.
             Open a new SPK file.
             ./
             spkopn_c ( SPK17, ifname, ncomch, &handle );

             /.
             Convert the classical elements to equinoctial elements
             (in the order compatible with type 17).
             ./
             eqel[0] = A;
             eqel[1] = ECC * sin ( OMEGA + NODE );
             eqel[2] = ECC * cos ( OMEGA + NODE );

             eqel[3] = M + OMEGA + NODE;

             eqel[4] = tan( INC/2.0 ) * sin( NODE );
             eqel[5] = tan( INC/2.0 ) * cos( NODE );

             eqel[6] =        DOMEGA + DNODE;
             eqel[7] = DMDT + DOMEGA + DNODE;
             eqel[8] = DNODE;

             /.
             Now add the segment.
             ./
             spkw17_c ( handle, BODY,  CENTER, FRMNAM, first,  last,
                        segid,  EPOCH, eqel,   RAPOL,  DECPOL );

             /.
             Close the SPK file.
             ./
             spkcls_c ( handle );

             return ( 0 );
          }

          When this program is executed, no output is presented on
          screen. After run completion, a new SPK type 17 exists in
          the output directory.
#### Restrictions
       None.
#### Literature_References
       None.
#### Author_and_Institution
       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       W.L. Taber          (JPL)
#### Version
       -CSPICE Version 1.0.1, 05-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard. Added complete
           code example based on existing example.

       -CSPICE Version 1.0.0, 21-JUN-1999 (NJB) (WLT)
#### Index_Entries
       Write a type 17 SPK segment
#### Link to routine spkw17_c source file spkw17_c.c

    Fri Dec 31 18:41:13 2021