Position, direction, distance and motion

This chapter reviews the methods that are used to measure direction and distance, so that position can be established either for large or small-scale ranges of movement. Position, as applied in measurement, invariably means position relative to some point that may be the Earth's north pole, the starting point of the motion of an object, or any other convenient reference point. Methods of determining position make use of distance and direction (angle) informationto specify a position either by using rectangular co-ordinates or by polar co-ordinates. There are two types of distance sensings, the sensing of distance to some fixed point and the sensing of distance moved, which are different both in principles and in methods that have to be used. In addition to position, direction, and distance, it also explains motion and its relationship with them.