The origin for a NED coordinate system is usually a point in the world frame (like take-off location). A heading angle of 0° will point toward the North, and +90° toward the East. Positive Z pointing downward can take some getting used to, but it is convenient as X and Y are then consistent with the right hand rule and normal navigation heading angles. This convention is called North-East-Down or NED. Ground (World) Coordinate SystemĪ popular ground or world coordinate system used for aircraft aligns the positive X, Y and Z axes with the directions of North, East and down. Care must therefore be taken when using roll, pitch and yaw to move an aircraft. Moreover, if the Pitch angle is positive, the direction will be backwards, or in the negative X axis. The definition of X, Y, Z, roll, pitch and yaw is consistent with aircraft body coordinate systems, but can sometimes be unintuitive to a developer seeing it for the first time.įor instance, if the aircraft rotates around the Pitch axis (Y axis) it will move in the X axis direction. When describing rotational movement, the X, Y and Z axes are renamed Roll, Pitch and Yaw. Using the coordinate right hand rule, the Z axis is then through the bottom of the aircraft.Īircraft translation in positive X, Y and Z is therefore defined in the Body Coordinate System as forward, right and downward translation respectively.Īircraft rotation is also described with these same axes using the coordinate right hand rule to define the direction of positive rotation. Three perpendicular axes are defined such that the origin is the center of mass, and the X axis is directed through the front of the aircraft and the Y axis through the right of the aircraft. The body coordinate system is relative to the aircraft itself. Many coordinate systems exist, but the two used in the DJI Mobile SDK are relative to the aircraft body (body frame), and relative to the ground (world frame). Description of aircraft movement is dependent on the location and orientation of coordinate axes that make a coordinate system (or frame of reference).
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