Azimuth of a direction

In a given place. One of the horizontal coordinates. The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle on the reference plane between the projected vector and a reference vector from the origin to the celestial south pole (for astronomers) or celestial north pole (for sailors) is the azimuth. The azimuth is counted positively in a counter-clockwise direction.