<para> 
This filter keeps or removes waypoints based on their proximity to an arc, 
which is a series of connected line segments similar to a route or a track 
but without any associated data other than the coordinates.  Optionally, it
can move each non-deleted waypoint over the closest segment of the arc.
</para>

<para> 
The arc may defined in a file whose name must be provided with the 
<option>file</option>, or the tracks or routes that have already been read.  That file contains pairs of coordinates for the 
vertices of the arc, one coordinate pair per line.  Comments may be
included by preceding them with a '#' character.  An arc file looks 
something like this sample:
</para>

<screen format="linespecific">	  
# Lima Road/SR3 north of Fort Wayne, Indiana 	  
41.150064468    -85.166207433 	  
41.150064468    -85.165371895 	  
41.149034500    -85.165157318 	  
41.147832870    -85.164771080 	  
41.146631241    -85.164384842 	  
41.144270897    -85.163655281 	  
41.141953468    -85.162882805
</screen>

<para> 
An arc file may optionally contain gaps in the arc.  You may specify 
such a gap by inserting a line containing "#break" either on a line by 
itself or after the coordinates of the starting point of the new arc segment.
</para>

<example id="example_arc_filter">         
<title>Using the arc filter</title>
<para>
Assuming the arc above is in a file called 
<filename moreinfo="none">lima_rd.txt</filename>, the following command line
would include only points within one mile of the section of Lima Road 
covered by the arc.
</para>
<para><userinput>gpsbabel -i geo -f 1.loc -x arc,file=lima_rd.txt,distance=1 -o mapsend -F 2.wpt</userinput></para>
</example>
      
