<para>
When this option is specified, each non deleted waypoint is moved over the
closest segment, or over the nearest point if <option>points</option> option
is used.
</para>
<para>
With the <option>rte</option> and <option>trk</option> options, if
is possible, altitude, creation_time and microsecond fields of waypoints
are updated by interpolation.
</para>
<para>
This is most useful if you are trying to obtain the closest points in
a road to some places. Or if you want to know the step times on some
places over the tracks. Also to transform waypoints in Garmin course points
(see <link linkend="fmt_gtrnctr">gtrnctr</link> and
<link linkend="fmt_garmin">garmin</link> format).
</para>
