onboard and these frames are also used to refer local observations. An important case in which this does not apply is aircraft. Aircraft observations are performed downwards and therefore normally NED axes convention applies. Nevertheless, when attitudes with respect to ground stations are given, a relationship between the local earth-bound frame and the onboard ENU frame is used. See also Attitude dynamics and control (spacecraft) Euler's rotation theorem Gyroscope Triad Method Rotation formalisms in three dimensions Geographic coordinate system Astronomical coordinate systems References Euclidean symmetries Rotation in three dimensions