Mate, you're a genius. Every single time I drive my car into a parking spot I have to get out at least once to physically check the location of the kerb and other random objects. This is a great way to save time and effort.
Please let us know when your microcontroller is ready for the market. Oh and if you can also let us know where you purchased the other parts from I'd appreciate it.
*fingers crossed it works on a 135i with iDrive*