SteeringAnglesToQ:

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   Convert sail steering angles to a quaternion.
   Clock angle is measured around the sun direction from the y axis of the
   reference frame. This function aligns the body y axis with the reference y 
   direction.
   If the reference quaternion is known it may be input directly.

   Since version 7.
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   Form:
   q = SteeringAnglesToQ( incidence, clock, uSun, r, v, c )
   q = SteeringAnglesToQ( incidence, clock, qRef )
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   ------
   Inputs
   ------
   incidence    (1,1)        Sun incidence angle (rad)
   clock        (1,1)        Clock angle (rad)
   qRef         (4,1)        Reference quaternion
      OR
   uSun         (3,1)        Unit vector to the sun
   r            (3,1)        Orbital position
   v            (3,1)        Orbital velocity
   c            (1,1)        Sign convention*   (Optional, default is 1)

   -------
   Outputs
   -------
   q       (4,1)     Inertial to body quaternion

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   See also QSail
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Children:

Common: Quaternion/Mat2Q
Common: Quaternion/Q2Mat
Common: Quaternion/QTForm
Common: Transform/Eul2Mat
Sail: Coordinates/QSail
Sail: Graphics/VisualizeSailAttitude