Index Page spkw20_c

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

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

       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
           SPICE(INVALIDCOUNT) is signaled.

       2)  If the interval length is not positive, SPICE(INTLENNOTPOS)
           is signaled.

       3)  If the name of the reference frame is not recognized,
           SPICE(INVALIDREFFRAME) is signaled.

       4)  If segment stop time is not greater then the begin time,
           SPICE(BADDESCRTIMES) is signaled.

       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. 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.

       7)  If the last non-blank character of `segid' occurs past index
           40, or if `segid' contains any nonprintable characters, the
           error will be diagnosed 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) will be signaled.

       9)  The error SPICE(EMPTYSTRING) is signaled if any input string
           does not contain at least one character, since the input strings
           cannot be converted to a Fortran-style string in this case.

       10) The error SPICE(NULLPOINTER) is signaled if any input string
           pointer is null.

#### 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)

#### Version

       -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

    Wed Apr  5 17:54:44 2017