Difference Between Azimuth and Bearing

Azimuth vs Bearing
 

When someone asks you for directions, we always give the person directions from a place that you both know, or agree upon. It may be the place you are at the moment or another location that you both know very well. The key idea here is that we need a commonly accepted position, or more formally a reference point to give the location. The extension of this seemingly simple idea can be seen anywhere a similar navigation problem is involved.

Since it is convenient to express a position on a sphere using angular displacement from a point, this method is widely used in surveying, navigation, astronomy, and other related subjects. Earth is a globe; therefore, any location on earth can be given using two independent angular displacement measures. These measures are often referred as the coordinates, and the system is known as the spherical coordinate system.

Azimuth is one of the coordinates used in the spherical coordinate system, which is the angular distance clockwise from the true north along the horizontal plane to a considered position. The bearing is also the angular distance measured along the horizontal, but the reference direction or point is a choice of the observer.

More about Azimuth

Azimuth is more formally defined in the generic form as the angle between the horizontal projection of a vector from the origin (or point of the observer) to the point considered and the reference vector on the horizontal plane. In most fields, this reference vector is considered as the line towards North or the north-south meridian. Being an angular measurement, it always has the units of angles, such as degrees, grads or angular mils.

The term azimuth is used in navigation, cartography, surveying, gunnery and many other fields. Each field has added variations to its basic definition, making it more relevant to the context of the subject.  Therefore, the azimuth described in astronomy is slightly different from the azimuth described in the cartography.

Azimuth can be determined by solar observation, astronomical direction method, equal altitudes method, method of repetitions, micrometer method and hour-angles of Polaris and of crossing of the almucantar.

More about Bearing

The bearing is the angle from a reference direction/line chosen by the observer to another direction. It is common to take the north or the south as the reference direction. Based on the situation or the application forward direction can also be considered as the reference direction.

In notation, azimuth is given as a plain angle since it is an accepted standard, but in the case of bearing, the reference direction and the direction of rotation are also mentioned. Consider the following examples.

Azimuth Bearing
45° East N 45 E 45° east of north
315° West N 45 W 45° west of north
337°  30’ North West N 22.5 W 22.5° west of north


What is the difference between Azimuth and Bearing?

• Azimuth is the angle from the north along the horizontal plane, and one of the two basic coordinates of the spherical coordinate system.

• The bearing is the angle along the horizontal plane, relative to a reference direction defined by the observer.

• For azimuth, the reference direction is the North, and the rotation is clockwise while, for the bearing, both reference and the rotation are defined by the observer

• While azimuth is a standard measure, bearing is more of a local measure based on the observer.

• From one perspective, azimuth is the bearing with the reference North and rotation clockwise.

• When denoting, azimuth is simply given in degrees (or grads or mils) while bearing is noted with the angle, reference direction and the direction of rotation.