BHinge:

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   Compute a transformation matrix from a bHinge data structure.
   There are four possiblities: 
     1) You can just input a transformation matrix by entering only the b field. 
     2) You can input a quaternion by just entering the q field.
     3) You can input an angle and axis of rotation (1=x,2=y,3=z).
        If no axis is specified, the rotation will be about the positive z-axis.
     4) If you enter the angle field and the b field, the output transformation 
        matrix will be the total rotation first through the angle about 
        the specified axis followed by rotation through the initial b matrix. 
        If no axis is specified, the rotation will be about the positive z-axis.


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   Form:
   b = BHinge( bHinge )
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   Inputs
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   bHinge.b     (3,3) Transformation matrix
         .q     (4,1) Quaternion
         .angle (1,1) Angle of rotation (radians)
         .axis  (1,1) Axis of rotation 1=x, 2=y, 3=z (default)
                      Positive integer means transform from
                      unrotated to rotated, negative means reverse
                      or
                (3,1) Axis of rotation - see AUToQ

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   Outputs
   -------
   b            (3,3)  Rotation matrix

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Children:

Common: Coord/AU2Q
Common: Coord/Q2Mat
Common: General/IsValidField