Incorporate distance-along-a-route doc. From Ron.

diff --git a/gpsbabel/README b/gpsbabel/README
index 9632df951e99f00813f2ac0ec11cf7b13b938c29..fafaaebf0aa6765d62cdad2582b5eaae851226ee 100644 (file)
--- a/gpsbabel/README
+++ b/gpsbabel/README
@@ -445,6 +445,43 @@ DATA FILTERS
        locations.  The result would be a GPX file that more than likely
        contains only unique points and point data.
 
+     DISTANCE ALONG A ROUTE
+
+        The arc filter is designed to include points 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.
+
+        The arc is defined in a file whose name must be provided with
+        the file=XXXX option to the filter.  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:
+
+         # 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
+
+        In addition to the file containing the arc, you should also
+        specify the maximum distance from the arc that will be accepted;
+        that distance is declared on the command line with the
+        distance=X.XX option to the filter.  Distance options may be
+        expressed in miles (distance=3M) or kilometers (distance=3K).
+        The default is zero miles.
+
+       For example, assuming the arc above is in a file called "lima_rd.txt":
+
+       gpsbabel -i geo -f 1.loc -x arc,file=lima_rd.txt,distance=1 \
+               -o mapsend -F 2.wpt
+
+       would include only points within one mile of the section of Lima Road
+       covered by the arc.
+
 
 COMMON USAGE