Index of Functions: A B C D E F G H I J K L M N O P Q R S T U V W X
Index Page spkw20_c

Table of contents

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

       spkw20_c ( Write SPK segment, type 20 )

       void spkw20_c  ( SpiceInt            handle,
                        SpiceInt            body,
                        SpiceInt            center,
                        ConstSpiceChar    * frame,
                        SpiceDouble         first,
                        SpiceDouble         last,
                        ConstSpiceChar    * segid,
                        SpiceDouble         intlen,
                        SpiceInt            n,
                        SpiceInt            polydg,
                        ConstSpiceDouble    cdata[],
                        SpiceDouble         dscale,
                        SpiceDouble         tscale,
                        SpiceDouble         initjd,
                        SpiceDouble         initfr  )

#### Abstract

       Write a type 20 segment to an SPK file.

#### Required_Reading

       DAF
       NAIF_IDS
       TIME
       SPK

#### Keywords

       EPHEMERIS

#### Brief_I/O

       VARIABLE  I/O  DESCRIPTION
       --------  ---  --------------------------------------------------
       handle     I   Handle of SPK file open for writing.
       body       I   NAIF code for ephemeris object.
       center     I   NAIF code for the center of motion of the 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.
       intlen     I   Length of time covered by logical record (days).
       n          I   Number of logical records in segment.
       polydg     I   Chebyshev polynomial degree.
       cdata      I   Array of Chebyshev coefficients and positions.
       dscale     I   Distance scale of data.
       tscale     I   Time scale of data.
       initjd     I   Integer part of begin time (TDB Julian date) of
                      first record.
       initfr     I   Fractional part of begin time (TDB Julian date) of
                      first record.
       MAXDEG     P   Maximum allowed degree of Chebyshev expansions.
       DTOL       P   Absolute tolerance for coverage bound checking.
       TOLSCL     P   Tolerance scale for coverage bound checking.

#### Detailed_Input

       handle      is the DAF handle of an SPK file to which a type 20
                   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 the
                   object identified by `body'.

       segid       is a segment identifier. An SPK segment identifier
                   may contain up to 40 characters, not counting the
                   terminating null character.

       intlen      is the length of time, in TDB Julian days, covered
                   by each set of Chebyshev polynomial coefficients
                   (each logical record).

       n           is the number of number of logical records to be
                   stored in the segment. There is one logical record
                   for each time period. Each logical record contains
                   three sets of Chebyshev coefficients---one for each
                   coordinate---and three position vector components.

       polydg      is the degree of each set of Chebyshev
                   polynomials, i.e. the number of Chebyshev
                   coefficients per coordinate minus one. `polydg' must
                   be less than or equal to the parameter MAXDEG.

       cdata       is an array containing all the sets of Chebyshev
                   polynomial coefficients and position components to
                   be placed in the new segment of the SPK file.
                   There are three sets of coefficients and position
                   components for each time interval covered by the
                   segment.

                   The coefficients and position components are
                   stored in `cdata' in order as follows:

                      the (degree + 1) coefficients for the first
                      coordinate of the first logical record,
                      followed by the X component of position at the
                      first interval midpoint.

                      the coefficients for the second coordinate,
                      followed by the Y component of position at the
                      first interval midpoint.

                      the coefficients for the third coordinate,
                      followed by the Z component of position at the
                      first interval midpoint.

                      the coefficients for the first coordinate for
                      the second logical record, followed by the X
                      component of position at the second interval
                      midpoint.

                      and so on.

                   A diagram follows:

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

       dscale,
       tscale      are, respectively, the distance scale of the input
                   position and velocity data in km, and the time
                   scale of the input velocity data in TDB seconds.

                   For example, if the input distance data have units
                   of astronomical units (AU), `dscale' should be set
                   to the number of km in one AU. If the input
                   velocity data have time units of Julian days, then
                   `tscale' should be set to the number of seconds per
                   Julian day (86400).

       initjd      is the integer part of the Julian ephemeris date of
                   initial epoch of the first record. `initjd' may be
                   less than, equal to, or greater than the initial
                   epoch.

       initfr      is the fractional part of the Julian ephemeris date
                   of initial epoch of the first record. `initfr' has
                   units of Julian days. `initfr' has magnitude strictly
                   less than 1 day. The sum

                      initjd + initfr

                   equals the Julian ephemeris date of the initial
                   epoch of the first record.

#### Detailed_Output

       None. This routine writes data to an SPK file.

#### Parameters

       The parameters listed below are not used directly in this
       routine; they are used by the underlying SPICELIB code that
       has been translated to C via f2c.

       MAXDEG         is the maximum allowed degree of the input
                      Chebyshev expansions. MAXDEG is declared in the
                      SPICELIB Fortran INCLUDE file spk20.inc.

                      The current value of MAXDEG is 50.

       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 20 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

                         initjd
                         initfr
                         intlen
                         n

                      See the -Exceptions section below for a description
                      of the error check using this tolerance.

                      The current value of TOLSCL is 1e-13.

#### Exceptions

       1)  If the number of sets of coefficients is not positive, the
           error SPICE(INVALIDCOUNT) 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 than or equal to 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 either the distance or time scale is non-positive, the
           error SPICE(NONPOSITIVESCALE) is signaled by a routine in the
           call tree of this routine.

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

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

#### Files

       A new type 20 SPK segment is written to the SPK file attached
       to `handle'.

#### Particulars

       This routine writes an SPK type 20 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.

#### Examples

       Suppose that you have in an array `cdata' sets of Chebyshev
       polynomial coefficients and position vectors representing the state
       of the moon (NAIF ID = 301), relative to the Earth-moon barycenter
       (NAIF ID = 3), in the J2000 reference frame, and you want to put
       these into a type 20 segment in an existing SPK file. The following
       code could be used to add one new type 20 segment. To add multiple
       segments, put the call to spkw20_c in a loop.

          #include "SpiceUsr.h"
               .
               .
               .

          /.
          First open the SPK file and get a handle for it.
          ./
          spkopa_c ( spknam, &handle );

          /.
          Create a segment identifier.
          ./
          segid = "MY_SAMPLE_SPK_TYPE_20_SEGMENT";

          /.
          Note that the interval length `intlen' has units
          of Julian days. The start time of the first record
          is expressed using two inputs: integer and fractional
          portions of the Julian ephemeris date of the start
          time.

          Write the segment.
          ./
          spkw20_c ( handle, 301,    3,      "J2000",
                     first,  last,   segid,  intlen,
                     n,      polydg, cdata,  dscale,
                     tscale, initjd, initfr          );

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

#### Restrictions

       None.

#### Literature_References

       None.

#### Author_and_Institution

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

#### Version

       -CSPICE Version 1.0.1, 10-AUG-2021 (JDR)

           Edited the header to comply with NAIF standard.

       -CSPICE Version 1.0.0, 23-DEC-2013 (NJB)

#### Index_Entries

       write SPK type_20 data segment

#### Link to routine spkw20_c source file spkw20_c.c

    Fri Dec 31 18:41:13 2021