<para>
  Specifying the <option>clean</option> flag makes the Gopal reader pass
  over the data and discard data that is probably incorrect such as the
  longitude and latitude of "0".
</para>
<para>
  If you happen to be a boater or pilot off the south short of Ghana,
  you may disagree that coordinates of "0, 0" are bad.
</para>

