quaternion: Added static member function to return a unit quaternion constructed from a vector

//- Return the unit quaternion (versor) from the given vector
    //  (w = sqrt(1 - |sqr(v)|))
    static inline quaternion unit(const vector& v);

src/OpenFOAM/primitives/quaternion/quaternion.H

@@ -140,12 +140,17 @@ public:
             const bool normalized
         );
 
-        //- Construct given scalar part, the vector part = vector::zero
+        //- Construct a real from the given scalar part, the vector part = zero
         inline explicit quaternion(const scalar w);
 
-        //- Construct a pure quaternion given the vector part, scalar part = 0
+        //- Construct a pure imaginary quaternion given the vector part,
+        //  the scalar part = 0
         inline explicit quaternion(const vector& v);
 
+        //- Return the unit quaternion (versor) from the given vector
+        //  (w = sqrt(1 - |sqr(v)|))
+        static inline quaternion unit(const vector& v);
+
         //- Construct a quaternion given the three Euler angles
         inline quaternion
         (

src/OpenFOAM/primitives/quaternion/quaternionI.H

@@ -78,6 +78,12 @@ inline Foam::quaternion::quaternion(const vector& v)
 {}
 
 
+inline Foam::quaternion Foam::quaternion::unit(const vector& v)
+{
+    return quaternion(sqrt(1 - magSqr(v)), v);
+}
+
+
 inline Foam::quaternion::quaternion
 (
     const rotationSequence rs,