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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

   void ckw05_c ( SpiceInt            handle,
                  SpiceCK05Subtype    subtyp,
                  SpiceInt            degree,
                  SpiceDouble         begtim,
                  SpiceDouble         endtim,
                  SpiceInt            inst,
                  ConstSpiceChar    * ref,
                  SpiceBoolean        avflag,
                  ConstSpiceChar    * segid, 
                  SpiceInt            n,
                  ConstSpiceDouble    sclkdp [],
                  const void        * packts,
                  SpiceDouble         rate,
                  SpiceInt            nints,
                  ConstSpiceDouble    starts []    )

Abstract

 
   Write a type 5 segment to a CK file. 
 

Required_Reading

 
   CK 
   NAIF_IDS 
   ROTATION
   TIME 
 

Keywords

 
   POINTING 
   FILES 
 

Brief_I/O

 
   Variable  I/O  Description 
   --------  ---  -------------------------------------------------- 
   handle     I   Handle of an open CK file. 
   subtyp     I   CK type 5 subtype code. 
   degree     I   Degree of interpolating polynomials.
   begtim     I   The beginning encoded SCLK of the segment. 
   endtim     I   The ending encoded SCLK of the segment. 
   inst       I   The NAIF instrument ID code. 
   ref        I   The reference frame of the segment. 
   avflag     I   True if the segment will contain angular velocity. 
   segid      I   Segment identifier. 
   n          I   Number of packets. 
   sclkdp     I   Encoded SCLK times. 
   packts     I   Array of packets. 
   rate       I   Nominal SCLK rate in seconds per tick. 
   nints      I   Number of intervals.
   starts     I   Encoded SCLK interval start times.
   MAXDEG     P   Maximum allowed degree of interpolating polynomial. 
 

Detailed_Input

 
  
   handle     is the handle of the CK file to which the segment will be
              written. The file must have been opened with write
              access.

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

   degree     is the degree of the polynomials used to interpolate the
              quaternions contained in the input packets.  All
              components of the quaternions are interpolated by
              polynomials of fixed degree.
 
   begtim,
   endtim     are the beginning and ending encoded SCLK times
              for which the segment provides pointing information.
              begtim must be less than or equal to endtim, and at least
              one data packet must have a time tag t such that
 
                        begtim  <  t  <  endtim
                                -     -
 
   inst       is the NAIF integer ID code for the instrument. 
 
   ref        is a character string which specifies the  
              reference frame of the segment. This should be one of 
              the frames supported by the SPICELIB routine NAMFRM 
              which is an entry point of FRAMEX. 
 
              The rotation matrices represented by the quaternions
              that are to be written to the segment transform the
              components of vectors from the inertial reference frame
              specified by ref to components in the instrument fixed
              frame. Also, the components of the angular velocity
              vectors to be written to the segment should be given
              with respect to ref.

              ref should be the name of one of the frames supported
              by the SPICELIB routine NAMFRM.


   avflag     is a boolean flag which indicates whether or not the 
              segment will contain angular velocity. 
 
   segid      is the segment identifier.  A CK segment identifier may 
              contain up to 40 characters, excluding the terminating
              null.
 
   packts     contains a time-ordered array of data packets
              representing the orientation of inst relative to the
              frame ref.  Each packet contains a SPICE-style quaternion
              and optionally, depending on the segment subtype,
              attitude derivative data, from which a C-matrix and an
              angular velocity vector may be derived.
 
              See the discussion of "Quaternion Styles" in the
              Particulars section below.

              The C-matrix represented by the Ith data packet is a
              rotation matrix that transforms the components of a
              vector expressed in the base frame specified by ref to
              components expressed in the instrument fixed frame at the
              time sclkdp(I).
 
              Thus, if a vector v has components x, y, z in the base
              frame, then v has components x', y', z' in the instrument
              fixed frame where:
 
                 [ x' ]     [          ] [ x ] 
                 | y' |  =  |   cmat   | | y | 
                 [ z' ]     [          ] [ z ] 
 
 
              The attitude derivative information in packts[i] gives
              the angular velocity of the instrument fixed frame at
              time sclkdp[i] with respect to the reference frame
              specified by ref.
 
              The direction of an angular velocity vector gives the
              right-handed axis about which the instrument fixed
              reference frame is rotating. The magnitude of the vector
              is the magnitude of the instantaneous velocity of the
              rotation, in radians per second.
 
              Packet contents and the corresponding interpolation
              methods depend on the segment subtype, and are as
              follows:

                 Subtype 0:  Hermite interpolation, 8-element packets.
                             Quaternion and quaternion derivatives
                             only, no angular velocity vector provided.
                             Quaternion elements are listed first,
                             followed by derivatives. Angular velocity
                             is derived from the quaternions and
                             quaternion derivatives.
 
                 Subtype 1:  Lagrange interpolation, 4-element packets.
                             Quaternion only. Angular velocity is
                             derived by differentiating the
                             interpolating polynomials.
 
                 Subtype 2:  Hermite interpolation, 14-element packets.
                             Quaternion and angular angular velocity
                             vector, as well as derivatives of each,
                             are provided. The quaternion comes first,
                             then quaternion derivatives, then angular
                             velocity and its derivatives.

                 Subtype 3:  Lagrange interpolation, 7-element packets.
                             Quaternion and angular velocity vector
                             provided. The quaternion comes first.
               
              Angular velocity is always specified relative to the base
              frame.
 
   rate       is the nominal rate of the spacecraft clock associated
              with inst.  Units are seconds per tick.  rate is used to
              scale angular velocity to radians/second.
 
   nints      is the number of intervals that the pointing instances
              are partitioned into.
 
   starts     are the start times of each of the interpolation
              intervals. These times must be strictly increasing and
              must coincide with times for which the segment contains
              pointing.
 

Detailed_Output

 
   None.  See Files section. 
 

Parameters

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

Exceptions

 
   If any of the following exceptions occur, this routine will return 
   without creating a new segment. 
 
   1)  If handle is not the handle of a C-kernel opened for writing 
       the error will be diagnosed by routines called by this 
       routine. 
 
   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 the first encoded SCLK time is negative then the error 
       SPICE(INVALIDSCLKTIME) is signaled. If any subsequent times 
       are negative the error will be detected in exception (5). 
 
   5)  If the encoded SCLK times are not strictly increasing, 
       the error SPICE(TIMESOUTOFORDER) is signaled. 
  
   6)  If the name of the reference frame is not one of those 
       supported by the routine framex_, the error 
       SPICE(INVALIDREFFRAME) is signaled. 
 
   7)  If the number of packets n is not at least 1, the error  
       SPICE(TOOFEWPACKETS) will be signaled. 
 
   8)  If nints, the number of interpolation intervals, is less than 
       or equal to 0, the error SPICE(INVALIDNUMINTS) is signaled. 
 
   9)  If the encoded SCLK interval start times are not strictly 
       increasing, the error SPICE(TIMESOUTOFORDER) is signaled. 
 
  10)  If an interval start time does not coincide with a time for 
       which there is an actual pointing instance in the segment, 
       then the error SPICE(INVALIDSTARTTIME) is signaled. 
 
  11)  This routine assumes that the rotation between adjacent 
       quaternions that are stored in the same interval has a 
       rotation angle of theta radians, where 
 
          0  <  theta  <  pi. 
             _ 
 
       The routines that evaluate the data in the segment produced 
       by this routine cannot distinguish between rotations of theta 
       radians, where theta is in the interval [0, pi), and 
       rotations of 
 
          theta   +   2 * k * pi 
 
       radians, where k is any integer.  These "large" rotations will 
       yield invalid results when interpolated.  You must ensure that 
       the data stored in the segment will not be subject to this 
       sort of ambiguity. 
 
  12)  If any quaternion is the zero vector, the error 
       SPICE(ZEROQUATERNION) is signaled. 
 
  13)  If the interpolation window size implied by degree is not 
       even, the error SPICE(INVALIDDEGREE) is signaled.  The window 
       size is degree+1 for Lagrange subtypes and is (degree+1)/2 
       for Hermite subtypes. 
 
  14)  If an unrecognized subtype code is supplied, the error  
       SPICE(NOTSUPPORTED) is signaled. 
 
  15)  If degree is not at least 1 or is greater than MAXDEG, the 
       error SPICE(INVALIDDEGREE) is signaled. 
 
  16)  If the segment descriptor bounds are out of order, the
       error SPICE(BADDESCRTIMES) is signaled.

  17)  If there is no element of SCLKDP that lies between BEGTIM and
       ENDTIM inclusive, the error SPICE(EMPTYSEGMENT) is signaled.

  18)  If RATE is zero, the error SPICE(INVALIDVALUE) is signaled.

  18)  If either the input frame or segment ID have null string
       pointers, the error SPICE(NULLPOINTER) is signaled.

  19)  If either the input frame or segment ID are zero-length
       strings, the error SPICE(EMPTYSTRING) is signaled.

Files

 
   A new type 5 CK segment is written to the CK file attached 
   to handle. 
 

Particulars

 
   This routine writes a CK type 5 data segment to the open CK 
   file according to the format described in the type 5 section of 
   the CK Required Reading. The CK file must have been opened with 
   write access. 
 

   Quaternion Styles
   -----------------

   There are different "styles" of quaternions used in
   science and engineering applications. Quaternion styles
   are characterized by

      - The order of quaternion elements

      - The quaternion multiplication formula

      - The convention for associating quaternions
        with rotation matrices

   Two of the commonly used styles are

      - "SPICE"

         > Invented by Sir William Rowan Hamilton
         > Frequently used in mathematics and physics textbooks

      - "Engineering"

         > Widely used in aerospace engineering applications


   CSPICE function interfaces ALWAYS use SPICE quaternions.
   Quaternions of any other style must be converted to SPICE
   quaternions before they are passed to CSPICE functions.


   Relationship between SPICE and Engineering Quaternions
   ------------------------------------------------------

   Let M be a rotation matrix such that for any vector V,

      M*V

   is the result of rotating V by theta radians in the
   counterclockwise direction about unit rotation axis vector A.
   Then the SPICE quaternions representing M are

      (+/-) (  cos(theta/2),
               sin(theta/2) A(1),
               sin(theta/2) A(2),
               sin(theta/2) A(3)  )

   while the engineering quaternions representing M are

      (+/-) ( -sin(theta/2) A(1),
              -sin(theta/2) A(2),
              -sin(theta/2) A(3),
               cos(theta/2)       )

   For both styles of quaternions, if a quaternion q represents
   a rotation matrix M, then -q represents M as well.

   Given an engineering quaternion

      QENG   = ( q0,  q1,  q2,  q3 )

   the equivalent SPICE quaternion is

      QSPICE = ( q3, -q0, -q1, -q2 )


   Associating SPICE Quaternions with Rotation Matrices
   ----------------------------------------------------

   Let FROM and TO be two right-handed reference frames, for
   example, an inertial frame and a spacecraft-fixed frame. Let the
   symbols

      V    ,   V
       FROM     TO

   denote, respectively, an arbitrary vector expressed relative to
   the FROM and TO frames. Let M denote the transformation matrix
   that transforms vectors from frame FROM to frame TO; then

      V   =  M * V
       TO         FROM

   where the expression on the right hand side represents left
   multiplication of the vector by the matrix.

   Then if the unit-length SPICE quaternion q represents M, where

      q = (q0, q1, q2, q3)

   the elements of M are derived from the elements of q as follows:

        +-                                                         -+
        |           2    2                                          |
        | 1 - 2*( q2 + q3 )   2*(q1*q2 - q0*q3)   2*(q1*q3 + q0*q2) |
        |                                                           |
        |                                                           |
        |                               2    2                      |
    M = | 2*(q1*q2 + q0*q3)   1 - 2*( q1 + q3 )   2*(q2*q3 - q0*q1) |
        |                                                           |
        |                                                           |
        |                                                   2    2  |
        | 2*(q1*q3 - q0*q2)   2*(q2*q3 + q0*q1)   1 - 2*( q1 + q2 ) |
        |                                                           |
        +-                                                         -+

   Note that substituting the elements of -q for those of q in the
   right hand side leaves each element of M unchanged; this shows
   that if a quaternion q represents a matrix M, then so does the
   quaternion -q.

   To map the rotation matrix M to a unit quaternion, we start by
   decomposing the rotation matrix as a sum of symmetric
   and skew-symmetric parts:

                                      2
      M = [ I  +  (1-cos(theta)) OMEGA  ] + [ sin(theta) OMEGA ]

                   symmetric                   skew-symmetric


   OMEGA is a skew-symmetric matrix of the form

                 +-             -+
                 |  0   -n3   n2 |
                 |               |
       OMEGA  =  |  n3   0   -n1 |
                 |               |
                 | -n2   n1   0  |
                 +-             -+

   The vector N of matrix entries (n1, n2, n3) is the rotation axis
   of M and theta is M's rotation angle.  Note that N and theta
   are not unique.

   Let

      C = cos(theta/2)
      S = sin(theta/2)

   Then the unit quaternions Q corresponding to M are

      Q = +/- ( C, S*n1, S*n2, S*n3 )

   The mappings between quaternions and the corresponding rotations
   are carried out by the CSPICE routines

      q2m_c {quaternion to matrix}
      m2q_c {matrix to quaternion}

   m2q_c always returns a quaternion with scalar part greater than
   or equal to zero.


   SPICE Quaternion Multiplication Formula
   ---------------------------------------

   Given a SPICE quaternion

      Q = ( q0, q1, q2, q3 )

   corresponding to rotation axis A and angle theta as above, we can
   represent Q using "scalar + vector" notation as follows:

      s =   q0           = cos(theta/2)

      v = ( q1, q2, q3 ) = sin(theta/2) * A

      Q = s + v

   Let Q1 and Q2 be SPICE quaternions with respective scalar
   and vector parts s1, s2 and v1, v2:

      Q1 = s1 + v1
      Q2 = s2 + v2

   We represent the dot product of v1 and v2 by

      <v1, v2>

   and the cross product of v1 and v2 by

      v1 x v2

   Then the SPICE quaternion product is

      Q1*Q2 = s1*s2 - <v1,v2>  + s1*v2 + s2*v1 + (v1 x v2)

   If Q1 and Q2 represent the rotation matrices M1 and M2
   respectively, then the quaternion product

      Q1*Q2

   represents the matrix product

      M1*M2

Examples

 
   This example code fragment writes a type 5 C-kernel segment
   for the Mars Express spacecraft bus to a previously opened CK
   file attached to handle.
 
      /.
      Include CSPICE interface definitions.
      ./
      #include "SpiceUsr.h"
                .
                .
                .
      /.
      Assume arrays of quaternions, angular velocities, and the
      associated SCLK times are produced elsewhere.  The software
      that calls ckw05_c must then decide how to partition these
      pointing instances into intervals over which linear
      interpolation between adjacent points is valid.
      ./
                 .
                 .
                 .
 
      /.
      The subroutine ckw05_c needs the following items for the
      segment descriptor:
 
         1) SCLK limits of the segment.
         2) Instrument code.
         3) Reference frame.
         4) The angular velocity flag.
         
      ./
      
      begtim = sclk [      0 ];
      endtim = sclk [ nrec-1 ];

      inst   =  -41000;
      ref    =  "J2000";
      avflag =  SPICETRUE;

      segid  = "MEX spacecraft bus - data type 5";
 
      /.
      Write the segment. 
      ./
      ckw05_c ( handle,  subtyp,  degree,  begtim,  endtim,  inst,   
                ref,     avflag,  segid,   n,       sclkdp,  packts, 
                rate,    nints,   starts                             );
                . 
                . 
                . 
      /.
      After all segments are written, close the C-kernel.
      ./
      ckcls_c ( handle );
      
 

Restrictions

 
   None. 
 

Literature_References

 
   None. 
 

Author_and_Institution

 
   N.J. Bachman    (JPL) 
   W.L. Taber      (JPL) 
   K.R. Gehringer  (JPL) 
   J.M. Lynch      (JPL) 
 

Version

 
   -CSPICE Version 2.0.0, 01-JUN-2010 (NJB)

      The check for non-unit quaternions has been replaced
      with a check for zero-length quaternions. (The
      implementation of the check is located in ckw05_.)

   -CSPICE Version 1.0.2, 27-FEB-2008 (NJB)

      Updated header; added information about SPICE 
      quaternion conventions.

   -CSPICE Version 1.0.1, 07-JAN-2005 (NJB)
 
      Description in Detailed_Input header section of
      constraints on BEGTIM and ENDTIM was corrected

   -CSPICE Version 1.0.0, 30-AUG-2002 (NJB) (WLT) (KRG) (JML)

Index_Entries

 
   write ck type_5 data segment 
 
Wed Apr  5 17:54:30 2017