ree rotation to obtain unit normals.
  </p>
    <h2>
      <a name="rendering">5. Rendering X-spline offset curves</a>
    </h2>
    <p>
    An X-spline offset curve is a continuous mathematical function.
    Rendering such a curve is most easily achieved by drawing a series
    of many short straight line segments that give the appearance
    of a smooth curve.  More segments are
    used for longer curves and for curves with sharper bends.
    For example, 
    the image below shows an X-spline drawn in R