My take on this, not: - on GPS, as mattbessey suggested. (precision: 2m max) - integrating accelerometer data : Very difficult, as the telephone would spin. A

My take on this, not: - on GPS, as mattbessey suggested. (precision: 2m max) - integrating accelerometer data : Very difficult, as the telephone would spin. Also: measurement errors are integrated too, so not too precise. Best option is time based: 1) Detect launch/landing time by looking at accelerometer spikes (easy, good time precision) 2) Altitude = 1/2 * g * ((timeLanding - timeLaunch) / 2) ^ 2. Air resistance negligible. g = 9.81 m/s^2.