<para>
This option is required.
</para>
<para>
This option specifies the name of the file containing the polygon to use for
filtering.  The format of the file is as described above.
</para>
<para>
GPSBabel supports converting any route or track to a file usable by this
filter; simply read it in the normal way and write it using the
<link linkend="fmt_arc">arc</link> file format.  Afterward, you will
need to make sure that the first point and the last point in the
file are the same, as the polygon filter depends on that.  You can do so
with any text editor.
</para>
