Ability to compare compare track to existing route and have it warn you if you are going off route

One of the things that I wish Google Maps/My Tracks would do is provide some 
sort of warning if you go off of a predetermined route.

How would this work?
In Google maps you design a route. As my tracks is recording a track, it 
compares points it's recording to ones on the pre-designed route. If it reports 
a variance of 500 feet or more from the predetermined route, it sends you some 
sort of warning. 

What is the purpose of this?
Recently when I went hiking I took a wrong turn and ended up going on a 
completely different hike that I had planned. If I could have told google maps 
where I was going, and have tracks warn me if I was off route that would have 
been prevented.

Original issue reported on code.google.com by renedriv...@gmail.com on 14 Jun 2010 at 10:17

Merged into: #15

anongit / mytracks

Ability to compare compare track to existing route and have it warn you if you are going off route #91