Not to pick on you, but hearing "per-determined height and GPS direction" makes me a bit nervous with anything related to human life. People follow GPS blindly and that's OK on roads with a driver, but in other applications it can lead to tragic results due to Dilution of Precision. The Flinders Islet crash is a prime example. [0][1]

[0] http://www.sailingmates.com/your-gps-can-kill-you/

[1] http://www.yachting.org.au/sport-services/safety/major-incid...