Direction of flight is defined by the vector between the users two hands and the flight speed is specified by the distance between the users hands.
Flight is stopped by moving the hands into a dead zone , a minimum hand separation.
API which makes this all possible. The image is a screen shot of THF in use over a basic landscape. The AVI can be downloaded here . One of the applications we built was the skeleton of a virtual kitchen. This was based on the actual kitchen in the Department of Computer Science at the University of York.