the positive z- or yaw axis always points up. World frame's origin is fixed at the center of gravity of the vehicle. By contrast, in case of air and sea vehicles like submarines, ships, airplanes etc., which use the NED-system (North-East-Down) as external reference (World frame), the vehicle's (body's) positive y- or pitch axis always points to its right, and its positive z- or yaw axis always points down. World frame's origin is fixed at the center of gravity of the vehicle. Finally, in case of space vehicles like space shuttles etc., a modification of the latter convention is used, where the vehicle's (body's) positive y- or pitch axis again always points to its right, and its positive z- or yaw axis always points down, but “down” now may have two different meanings: If a so-called local frame is used as external reference, its positive z-axis points “down” to the center of the earth as it does in case of the earlier mentioned NED-system, but if the inertial frame is used as reference, its positive z-axis will point now to the north celestial pole, and its positive x-axis to the Vernal Equinox or some other reference meridian. Frames mounted on vehicles Specially for aircraft, these frames do not need to agree with the earth-bound frames in the up-down line. It must be agreed what ENU and NED mean in this context. Conventions for land vehicles For land vehicles it is rare to describe their complete orientation, except when speaking about electronic stability control or satellite navigation. In this case, the convention is normally the one of the adjacent drawing, where RPY stands for roll-pitch-yaw. Conventions for sea vehicles As well as aircraft, the same terminology is used for the motion of ships and boats. Some words commonly used were introduced in maritime navigation. For example, the yaw angle or heading, has a nautical origin, with the meaning of "bending out of the course". Etymologically, it is related with the verb 'to go'. It is related to the concept of bearing. It is typically assigned the shorthand notation . Conventions for aircraft local reference frames Coordinates to describe an aircraft attitude (Heading, Elevation and Bank) are normally given relative to a reference control frame located in a control tower, and therefore ENU, relative to the position of the control tower on the earth surface. Coordinates to describe observations made from an