Their are absolute rotary position sensors that can measure the magnetic field orientation of a magnet. They give an analog output proportional to the angular position. Cherry electronics has a nice automotive grade unit that is better than a continues rotation pot. Mouser carries them.
http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMvhQj7WZhFIAPb0P%2f L5OpbJhxqh3niR4xw%3d
The nice thing about them is they always give absolute position.