>>> r
    Ray3D(Point3D(2, 3, 4), Point3D(3, 5, 0))
    >>> r.points
    (Point3D(2, 3, 4), Point3D(3, 5, 0))
    >>> r.source
    Point3D(2, 3, 4)
    >>> r.xdirection
    oo
    >>> r.ydirection
    oo
    >>> r.direction_ratio
    [1, 2, -4]

    Nr(