cribes how the tangent is used to
    draw an offset curve.  
  </p>
    <h2>
      <a name="offset-curves">2. Offset curves</a>
    </h2>
    <p>
    Following 
    <a href="#chen+lin">Lin and Chen, 2014</a>, if we have a planar
    (two-dimensional) parametric curve
    \(\mathbf{r}=\mathbf{r}(t)\), \(t \in [0, 1]\),
    then an offset curve with variable
    offset is given by  

    $$\mathbf{r}_0(t)=\mathbf{r}(t) + d(t)\mathbf{n}(t)$$

    where \(\mathbf{n}(t)\) is the unit normal vector at each
    p