<para>
This option is not required, but if it is not specified the distance
defaults to zero miles, which isn't very useful.
</para>
<para>
This option specifies the maximum distance a point may be from the arc
without being discarded.  Points that are closer to the arc are kept, while
points that are further away are discarded.
</para>
<para>
The units may be specified by appending a suffix to the supplied number:
</para>
<simplelist type="vert">
<member>'m' for meters, e.g. 3500.0m</member>
<member>'ft' or 'feet' for feet, e.g. 11483ft</member>
<member>'k' or 'km' for kilometers, e.g 3.5000km</member>
<member>'nm' for nautical miles, e.g. 1.8898nm</member>
<member>'mi' for miles, e.g. 2.1748mi</member>
<member>'fa' for fathoms, e.g. 1913.82fa</member>
</simplelist>
<para>
If no units are specified, the units are assumed to be miles.
</para>
