We can calculate the UAV heading (flight directions) from multiple consecutive GPS readings if the UAV is moving. However, for a hovering, this method would not work and we may need a magnetic compass or a magnetometer (like MicroMag 3-Axis Magnetometer from SparkFun).
GPS receivers (without DGPS or WAAS corrections) do not provide accurate altitude information. In order to maintain accurate altitude, a pitot-static may be used.
Is there anyone in this DIY Drones network who used a pilot-static sensor suite for his/her Ardupiloted UAV?