public Matrix3f toRotationMatrix() {
        Matrix3f matrix = new Matrix3f();
        return toRotationMatrix(matrix);
    }
Converts to an equivalent rotation matrix. The current instance is
unaffected.

<p>Note: the result is created from a normalized version of the current
instance.

@return a new 3x3 rotation matrix
jme3-core/src/main/java/com/jme3/math/Quaternion.java