d.  The relationships between vectorial and pixel coordinates is
    explained.</p>


    <a name="section-1">
    <h3>
      1. Vectorial versus pixel coordinates
    </h3>

    <p>This sub-section explains the differences between vectorial and pixel
    coordinates.  To make things clear, brackets will be used to describe
    pixel coordinates, e.g. [3,5], while parentheses will be used for
    vectorial ones, e.g. (-2,3.5).</p>

    <p>In the pixel case, as we use the <em>Y&nbsp;upwards</em> convention;
