[GRASS-user] Forcing polyline nodes through a point

[Dwight Needels]

I am trying to create a map of hiking trails based on GPS data. If  
anyone can point me to a tutorial that discusses the techniques and  
issues involved, I would appreciate it. Meanwhile, a couple of  
specific questions.

I have a series of GPS tracks that have been brought into GRASS as  
polylines, and a series of time-averaged waypoints that have been  
brought into GRASS as points. The lines represent segments of color- 
blazed trails, and the waypoints represent higher-quality measurements  
of trail termini and intersections.

I am looking for a way to force the polylines (from GPS tracks) to  
terminate at the points (from averaged waypoints). One possibility  
would be to snap each terminal node to the nearest point (within a  
threshold), with the point coordinates taking precedence. I think I  
would prefer, instead, to have the point appended to the end of the  
line, becoming the new node (followed by a cleanup step with  
v.generalize).

Does anyone have any idea how I might accomplish either of these  
things? Is there a better/easier method?

With some up-front processing I could ensure that each trail segment  
terminates near an averaged waypoint. However, it would be  
considerably less work if I could automatically split a polyline at  
the vertex that is closest to a point (within a threshold) before  
processing as above. This would allow me to smooth (straighten) the  
trails while still maintaining sharp turns at important locations such  
as switchbacks in the trail.

Is this feasible?

Thanks, -Dwight