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Index Page spkw02_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

       spkw02_c ( Write SPK segment, type 2 )

       void spkw02_c ( SpiceInt                handle,
                       SpiceInt                body,
                       SpiceInt                center,
                       ConstSpiceChar        * frame,
                       SpiceDouble             first,
                       SpiceDouble             last,
                       ConstSpiceChar        * segid,
                       SpiceDouble             intlen,
                       SpiceInt                n,
                       SpiceInt                polydg,
                       ConstSpiceDouble        cdata [],
                       SpiceDouble             btime     )

#### Abstract

       Write a type 2 segment to an SPK file.

#### Required_Reading

       NAIF_IDS
       SPC
       SPK

#### Keywords

       EPHEMERIS

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       MAXDEG     P   Maximum degree of Chebyshev expansions.
       TOLSCL     P   Scale factor used to compute time bound tolerance.
       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.
       intlen     I   Length of time covered by logical record.
       n          I   Number of coefficient sets.
       polydg     I   Chebyshev polynomial degree.
       cdata      I   Array of Chebyshev coefficients.
       btime      I   Begin time of first logical record.

#### Detailed_Input

       handle      is the DAF handle of an SPK file to which a type 2
                   segment is to be added. The SPK file must be open for
                   writing.

       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 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.

       intlen      is the length of time, in seconds, covered by each set of
                   Chebyshev polynomial coefficients (each logical record).
                   Each set of Chebyshev coefficients must cover this fixed
                   time interval, `intlen'.

       n           is the number of sets of Chebyshev polynomial
                   coefficients for coordinates (number of logical records)
                   to be stored in the segment. There is one set of
                   Chebyshev coefficients for each time period.

       polydg      is the degree of each set of Chebyshev polynomials used
                   to represent the ephemeris information. That is, the
                   number of Chebyshev coefficients per coordinate minus
                   one. `polydg' must not exceed MAXDEG (see -Parameters
                   below).

       cdata       is a time-ordered array of `n' sets of Chebyshev polynomial
                   coefficients to be placed in the segment of the SPK file.
                   Each set has size setsz = 3*(polydg+1). The coefficients
                   are stored in `cdata' in order as follows:

                      the (polydg + 1) coefficients for the first
                      coordinate of the first logical record,

                      the coefficients for the second coordinate,

                      the coefficients for the third coordinate,

                      the coefficients for the first coordinate for
                      the second logical record, ...

                      and so on.

       btime       is the begin time (seconds past J2000 TDB) of first set
                   of Chebyshev polynomial coefficients (first logical
                   record). `first' is an appropriate value for `btime'.

#### Detailed_Output

       None.

       The routine writes to the SPK file referred to by `handle' a type 02
       SPK segment containing the data in `cdata'.

       See the -Particulars section for details about the structure of a
       type 02 SPK segment.

#### Parameters

       The parameters below are declared in the Fortran include file
       spk02.inc, which is part of the Fortran SPICE Toolkit (aka
       SPICELIB). The values of those parameters are used in CSPICE code
       generated by running f2c on SPICELIB source code. They are not
       directly referenced by code in this module.

          MAXDEG         is the maximum allowed degree of the input
                         Chebyshev expansions.

                         The value of MAXDEG is 27.

          TOLSCL         is a tolerance scale factor (also called a
                         "relative tolerance") used for time coverage bound
                         checking. TOLSCL is unitless. TOLSCL produces a
                         tolerance value via the formula

                            TOL = TOLSCL * max( abs(first), abs(last) )

                         where `first' and `last' are the coverage time
                         bounds of a type 2 segment, expressed as seconds
                         past J2000 TDB.

                         The resulting parameter TOL is used as a tolerance
                         for comparing the input segment descriptor time
                         bounds to the first and last epoch covered by the
                         sequence of time intervals defined by the inputs
                         to spkw02_c:

                            btime
                            intlen
                            n

                         The value of TOLSCL is 1.e-13.

#### Exceptions

       1)  If the number of sets of coefficients is not positive, the
           error SPICE(NUMCOEFFSNOTPOS) is signaled by a routine in the
           call tree of this routine.

       2)  If the interval length is not positive, the error
           SPICE(INTLENNOTPOS) is signaled by a routine in the call tree
           of this routine.

       3)  If the name of the reference frame is not recognized, the
           error SPICE(INVALIDREFFRAME) is signaled by a routine in the
           call tree of this routine.

       4)  If segment stop time is not greater then the begin time, the
           error SPICE(BADDESCRTIMES) is signaled by a routine in the
           call tree of this routine.

       5)  If the start time of the first record exceeds the descriptor
           begin time by more than a computed tolerance, or if the end
           time of the last record precedes the descriptor end time by
           more than a computed tolerance, the error SPICE(COVERAGEGAP)
           is signaled by a routine in the call tree of this routine. See
           the -Parameters section above for a description of the
           tolerance.

       6)  If the input degree `polydg' is less than 0 or greater than
           MAXDEG, the error SPICE(INVALIDDEGREE) is signaled by a
           routine in the call tree of this routine.

       7)  If the last non-blank character of `segid' occurs past index 40,
           or if `segid' contains any nonprintable characters, an error is
           signaled by a routine in the call tree of this routine.

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

       9)  If any of the `frame' or `segid' input strings has zero
           length, the error SPICE(EMPTYSTRING) is signaled.

#### Files

       A new type 2 SPK segment is written to the SPK file attached
       to handle.

#### Particulars

       This routine writes an SPK type 2 data segment to the designated
       SPK file, according to the format described in the SPK Required
       Reading.

       Each segment can contain data for only one target, central body,
       and reference frame. The Chebyshev polynomial degree and length
       of time covered by each logical record are also fixed. However,
       an arbitrary number of logical records of Chebyshev polynomial
       coefficients can be written in each segment. Minimizing the
       number of segments in an SPK file will help optimize how the SPICE
       system accesses the file.

       The ephemeris data supplied to the type 2 SPK writer is packed
       into an array as a sequence of records. The logical data records
       are stored contiguously:

          +----------+
          | Record 1 |
          +----------+
          | Record 2 |
          +----------+
              ...
          +----------+
          | Record n |
          +----------+

       The contents of an individual record are:

          +--------------------------------------+
          | Coeff set for X position component   |
          +--------------------------------------+
          | Coeff set for Y position component   |
          +--------------------------------------+
          | Coeff set for Z position component   |
          +--------------------------------------+

       Each coefficient set has the structure:

          +--------------------------------------+
          | Coefficient of T_0                   |
          +--------------------------------------+
          | Coefficient of T_1                   |
          +--------------------------------------+
                            ...
          +--------------------------------------+
          | Coefficient of T_POLYDG              |
          +--------------------------------------+

       Where T_n represents the Chebyshev polynomial
       of the first kind of degree n.

#### 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) This example demonstrates how to create an SPK type 2 kernel
          containing only one segment, given a set of Chebychev
          coefficients and their associated epochs.

          Example code begins here.

          /.
             Program spkw02_ex1
          ./
          #include "SpiceUsr.h"

          int main( )
          {

             /.
             Define the segment identifier parameters.
             ./
             #define SPK2         "spkw02_ex1.bsp"
             #define REF          "J2000"
             #define BODY         3
             #define CENTER       10
             #define CHBDEG       2
             #define NRECS        4
             #define RECSIZ     ( 3*(CHBDEG+1) )

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

             SpiceDouble          first;
             SpiceDouble          intlen;
             SpiceDouble          last;

             SpiceInt             handle;
             SpiceInt             ncomch;

             /.
             Define the coefficients.
             ./
             SpiceDouble          recrds [NRECS][RECSIZ] = {
                                       {1.0101, 1.0102, 1.0103,
                                        1.0201, 1.0202, 1.0203,
                                        1.0301, 1.0302, 1.0303},
                                       {2.0101, 2.0102, 2.0103,
                                        2.0201, 2.0202, 2.0203,
                                        2.0301, 2.0302, 2.0303},
                                       {3.0101, 3.0102, 3.0103,
                                        3.0201, 3.0202, 3.0203,
                                        3.0301, 3.0302, 3.0303},
                                       {4.0101, 4.0102, 4.0103,
                                        4.0201, 4.0202, 4.0203,
                                        4.0301, 4.0302, 4.0303} };

             /.
             Set the start and end times of interval covered by
             segment, and the length of time covered by logical
             record.
             ./
             first  = 100.0;
             last   = 500.0;
             intlen = 100.0;

             /.
             `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 = "Type 2 SPK internal file name.";
             segid  = "SPK type 2 test segment";

             /.
             Open a new SPK file.
             ./
             spkopn_c ( SPK2, ifname, ncomch, &handle );

             /.
             Write the segment.
             ./
             spkw02_c ( handle, BODY,   CENTER, REF,    first, last,
                        segid,  intlen, NRECS,  CHBDEG, recrds, first );

             /.
             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 2 exists in
          the output directory.

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

       N.J. Bachman        (JPL)
       J. Diaz del Rio     (ODC Space)
       K.S. Zukor          (JPL)

#### Version

       -CSPICE Version 2.0.1, 10-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard. Added complete
           example code from existing fragment.

           Extended "polydg" and "cdata" arguments description to provide the
           size of the Chebyshev polynomials sets. Moved the details of the SPK
           structure from "cdata" argument description to -Particulars section.

           Added entry #4 in -Exceptions section.

       -CSPICE Version 2.0.0, 09-JAN-2014 (NJB)

           Relaxed test on relationship between the time bounds of the
           input record set (determined by `btime', `intlen', and `n') and
           the descriptor bounds `first' and `last'. Now the descriptor
           bounds may extend beyond the time bounds of the record set by a
           ratio computed using the parameter TOLSCL (see -Parameters above
           for details). Added checks on input polynomial degree.

       -CSPICE Version 1.0.0, 21-JUL-1999 (NJB) (KSZ)

#### Index_Entries

       write SPK type_2 data segment

#### Link to routine spkw02_c source file spkw02_c.c

    Fri Dec 31 18:41:13 2021