Write a type 18 segment to an SPK file. 

   NAIF_IDS 
   SPC 
   SPK 
   TIME 

   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   handle     I   Handle of an SPK file open for writing. 
   subtyp     I   SPK type 18 subtype code.
   body       I   NAIF code for an ephemeris object. 
   center     I   NAIF code for center of motion of body. 
   frame      I   Reference frame name. 
   first      I   Start time of interval covered by segment. 
   last       I   End time of interval covered by segment. 
   segid      I   Segment identifier. 
   degree     I   Degree of interpolating polynomials. 
   n          I   Number of states. 
   states     I   Array of states. 
   epochs     I   Array of epochs corresponding to states. 
   MAXDEG     P   Maximum allowed degree of interpolating polynomial. 

   handle         is the file handle of an SPK file that has been 
                  opened for writing. 

   subtyp         is an integer code indicating the subtype of the
                  the segment to be created.   

   body           is the NAIF integer code for an ephemeris object 
                  whose state relative to another body is described 
                  by the segment to be created. 

   center         is the NAIF integer code for the center of motion 
                  of the object identified by body. 

   frame          is the NAIF name for a reference frame 
                  relative to which the state information for body 
                  is specified. 

   first, 
   last           are, respectively, the start and stop times of 
                  the time interval over which the segment defines 
                  the state of body. 

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

   degree         is the nominal degree of the polynomials used to
                  interpolate the states contained in the input
                  packets.  All components of the state vectors are 
                  interpolated by polynomials of the specified
                  degree, except near the segment boundaries, 
                  or if the total number of states in the segment
                  is too few to allow interpolation using the
                  specified degree.

   n              is the number of packets in the input packet
                  array. 

   packts         contains a time-ordered array of data packets 
                  representing geometric states of body relative  
                  to center, specified relative to frame.  The  
                  packet structure depends on the segment subtype 
                  as follows: 

                     Type 0 (indicated by code S18TP0): 

                         x,  y,  z,  dx/dt,  dy/dt,  dz/dt, 
                         vx, vy, vz, dvx/dt, dvy/dt, dvz/dt 

                     where x, y, z represent Cartesian position 
                     components and  vx, vy, vz represent Cartesian 
                     velocity components.  Note well:  vx, vy, and 
                     vz *are not necessarily equal* to the time 
                     derivatives of x, y, and z.  This packet  
                     structure mimics that of the Rosetta/MEX orbit 
                     file from which the data are taken. 

                     Type 1 (indicated by code S18TP1): 

                         x,  y,  z,  dx/dt,  dy/dt,  dz/dt 

                     where x, y, z represent Cartesian position 
                     components and  vx, vy, vz represent Cartesian 
                     velocity components. 

                  Position units are kilometers, velocity units  
                  are kilometers per second, and acceleration units 
                  are kilometers per second per second. 


   epochs         is an array of epochs corresponding to the members 
                  of the packets array.  The epochs are specified as 
                  seconds past J2000, TDB. 

   None.  See $Particulars for a description of the effect of this 
   routine. 

   MAXDEG         is the maximum allowed degree of the interpolating 
                  polynomial.  If the value of MAXDEG is increased, 
                  the CSPICE routine spkpvn_ must be changed 
                  accordingly.  In particular, the size of the 
                  record passed to SPKRnn and SPKEnn must be 
                  increased, and comments describing the record size 
                  must be changed. 

   This routine writes an SPK type 18 data segment to the open SPK 
   file according to the format described in the type 18 section of 
   the SPK Required Reading. The SPK file must have been opened with 
   write access. 

  Suppose that you have states and are prepared to produce 
   a segment of type 18 in an SPK file. 

   The following code fragment could be used to add the new segment 
   to a previously opened SPK file attached to handle. The file must 
   have been opened with write access. 

      #include "SpiceUsr.h"
           .
           .
           .

      /.
      Create a segment identifier. 
      ./
      #define  SEGID  "MY_SAMPLE_SPK_TYPE_18_SEGMENT" 


      /.
      Write the segment. 
      ./        
      spkw18_c ( handle,  subtyp,  body,    center,   
                 frame,   first,   last,    segid,   
                 degree,  n,       states,  epochs );

   None. 

   If any of the following exceptions occur, this routine will return 
   without creating a new segment. 

   1)  If frame is not a recognized name, the error 
       SPICE(INVALIDREFFRAME) is signaled. 

   2)  If the last non-blank character of segid occurs past index 40, 
       the error SPICE(SEGIDTOOLONG) is signaled. 

   3)  If segid contains any nonprintable characters, the error 
       SPICE(NONPRINTABLECHARS) is signaled. 

   4)  If degree is not at least 1 or is greater than MAXDEG, the 
       error SPICE(INVALIDDEGREE) is signaled. 

   5)  If the window size implied by DEGREE is odd, the error 
       SPICE(INVALIDDEGREE) is signaled. 

   6)  If the number of packets n is not at least 1, 
       the error SPICE(TOOFEWSTATES) will be signaled.

   7)  If first is greater than or equal to last then the error 
       SPICE(BADDESCRTIMES) will be signaled. 

   8)  If the elements of the array epochs are not in strictly 
       increasing order, the error SPICE(TIMESOUTOFORDER) will be 
       signaled. 

   9)  If the first epoch epochs[0] is greater than first, the error 
       SPICE(BADDESCRTIMES) will be signaled. 

   10) If the last epoch epochs[n-1] is less than last, the error 
       SPICE(BADDESCRTIMES) will be signaled. 

   11) If either the input frame or segment ID string pointer is null,
       the error SPICE(NULLPOINTER) is signaled.

   12) If either the input frame or segment ID string is empty,
       the error SPICE(EMPTYSTRING) is signaled.

   A new type 18 SPK segment is written to the SPK file attached 
   to HANDLE. 

   N.J. Bachman   (JPL) 

   None. 

   -CSPICE Version 1.0.1, 29-APR-2003 (NJB)

       Description of error condition arising from invalid window
       size was corrected.

   -CSPICE Version 1.0.0, 16-AUG-2002 (NJB)

   write spk type_18 ephemeris data segment