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Required Reading


   CSPICE_Q2M calculates the 3x3 double precision, rotation matrix 
   corresponding to a specified unit quaternion.

   For important details concerning this module's function, please refer to
   the CSPICE routine q2m_c.


      q   is a unit length double precision 4-vector representing
           a SPICE-style quaternion.

           Note that multiple styles of quaternions are in use.
           This routine will not work properly if the input
           quaternions do not conform to the SPICE convention.
           See the Particulars section for details.
      the call:
      cspice_q2m, q, r
      r   a 3x3 double precision rotation matrix representation of
          the quaternion.


   Any numerical results shown for this example may differ between
   platforms as the results depend on the SPICE kernels used as input
   and the machine specific arithmetic implementation.

      ;; Define a unit quaternion.
      q = [ sqrt(2.d)/2.d, 0.d, 0.d, -sqrt(2.d)/2.d]
      print, q
   IDL outputs:   0.70710678    0.0000000    0.0000000  -0.70710678
      ;; Confirm q satisfies || q || = 1. Calculate q * q.
      print, transpose(q) # q
   IDL outputs:  1.0000000
      ;; Convert the quaternion to a matrix form.
      cspice_q2m, q, m
      print, m
   IDL outputs:
          0.0000000       1.0000000       0.0000000
         -1.0000000       0.0000000       0.0000000
          0.0000000       0.0000000       1.0000000
   Please note, the call sequence:
      cspice_m2q, r, q
      cspice_q2m, q,r
   preserves 'r' except for round-off error. Yet, the call sequence:
      cspice_q2m, q,r
      cspice_m2q, r, q
   may preserve 'q' or return '-q'.


   About SPICE quaternions 
   There are (at least) two popular "styles" of quaternions; these 
   differ in the layout of the quaternion elements, the definition 
   of the multiplication operation, and the mapping between the set 
   of unit quaternions and corresponding rotation matrices. 
   SPICE-style quaternions have the scalar part in the first 
   component and the vector part in the subsequent components. The 
   SPICE convention, along with the multiplication rules for SPICE 
   quaternions, are those used by William Rowan Hamilton, the 
   inventor of quaternions. 
   Another common quaternion style places the scalar component 
   last.  This style is often used in engineering applications. 

Required Reading



   -Icy Version 1.0.1, 06-NOV-2005, EDW (JPL)

      Updated Particulars section to include the 
      "About SPICE Quaternions" description. Recast
      the I/O section to meet Icy format standards.

   -Icy Version 1.0.0, 16-JUN-2003, EDW (JPL)


   quaternion to matrix 

Wed Apr  5 17:58:03 2017