overl4nder
Observer
A few years ago, I wrote this article about offroad GPS navigation. I know its old, but most of the information is still relevant, and the software I walk about still exist and do quite well.
Here is the link
http://www.team-bhp.com/advice/offroad-gps-navigation-concepts-and-software
Here is the link
http://www.team-bhp.com/advice/offroad-gps-navigation-concepts-and-software