navigation Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation ...

, bearing or azimuth is the horizontal

angle In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles ...

between the direction of an object and

north North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...

or another object. The angle value can be specified in various

angular units In Euclidean geometry, an angle is the figure formed by two rays, called the '' sides'' of the angle, sharing a common endpoint, called the ''vertex'' of the angle. Angles formed by two rays lie in the plane that contains the rays. Angles a ...

, such as degrees, mils, or grad. More specifically: *

Absolute bearing In navigation, bearing or azimuth is the horizontal angle between the direction of an object and north or another object. The angle value can be specified in various angular units, such as degrees, mils, or grad. More specifically: * Abso ...

refers to the angle between the magnetic north (''magnetic bearing'') or true

(''true bearing'') and an object. For example, an object to due east would have an absolute bearing of 90 degrees. Thus, it is the same as

azimuth An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematical ...

.U.S. Army, ''Advanced Map and Aerial Photograph Reading'', Headquarters, War Department, Washington, D.C. (17 September 1941), pp. 24-2

/ref> * #Relative, Relative bearing refers to the angle between the craft's forward direction ( heading) and the location of another object. For example, an object relative bearing of 0 degrees would be immediately in front; an object relative bearing 180 degrees would be behind. Bearings can be measured in mils, points, or degrees. Thus, it is the same as an ''azimuth difference'' (modulo +/- 360 degrees). Alternatively, the US Army defines the ''bearing'' from point A to point B as the smallest angle between the

ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (gr ...

AB and either north south, whichever is closest. The bearing is expressed in terms of 2 characters and 1 number: first, the character is either N or S; next is the angle numerical value; third, the character representing the

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the '' perpendicular symbol'', ⟂. It c ...

direction, either E or W. The bearing angle value will always be less than 90 degrees. For example, if Point B is located exactly southeast of Point A, the bearing from Point A to Point B is "S 45° E".U.S. Army, Map Reading and Land Navigation, FM 21-26, Headquarters, Dept. of the Army, Washington, D.C. (28 March 1956), ch. 3, pp. 69-70 For example, if the bearing between Point A and Point B is S 45° E, the azimuth between Point A and Point B is 135°. Azimuths and bearings

Types

Absolute

In nautical

the absolute bearing is the

clockwise Two-dimensional rotation can occur in two possible directions. Clockwise motion (abbreviated CW) proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite ...

angle between

and an object observed from the vessel. If the north used as reference is the true geographical

then the bearing is a ''true bearing'' whereas if the reference used is magnetic north then the bearing is a ''magnetic bearing''. An absolute bearing is measured with a

bearing compass A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with ...

. The measurement of absolute bearings of fixed landmarks and other navigation aids is useful for the navigator because this information can be used on the

nautical chart A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land ( topographic map), natural features of the seabed, details of the co ...

together with simple geometrical techniques to aid in determining the position of the vessel. A ''grid bearing'' (also known as grid azimuth) is measured in relation to the fixed horizontal reference plane of grid north, that is, using the direction northwards along the grid lines of the

map projection In cartography, map projection is the term used to describe a broad set of transformations employed to represent the two-dimensional curved surface of a globe on a plane. In a map projection, coordinates, often expressed as latitude and l ...

as a reference point. A ''compass bearing'', as in vehicle or marine navigation, is measured in relation to the magnetic compass of the navigator's vehicle or vessel (if aboard ship). It should be very close to the magnetic bearing. The difference between a magnetic bearing and a compass bearing is the deviation caused to the compass by ferrous metals and local magnetic fields generated by any variety of vehicle or shipboard sources (steel vehicle bodies/frames or vessel hulls, ignition systems, etc.)

Relative

In nautical navigation the relative bearing of an object is the clockwise angle from the heading of the vessel to a straight line drawn from the observation station on the vessel to the object. The relative bearing is measured with a pelorus or other optical and electronic aids to navigation such as a

periscope A periscope is an instrument for observation over, around or through an object, obstacle or condition that prevents direct line-of-sight observation from an observer's current position. In its simplest form, it consists of an outer case with ...

sonar system Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...

, and

radar system Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weat ...

s. Since World War II, relative bearings of such diverse point sources have been and are calibrated carefully to one another. The

United States Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage ...

operates a special range off Puerto Rico and another on the west coast to perform such systems integration. Relative bearings then serve as the baseline data for converting relative directional data into true bearings (N-S-E-W, relative to the Earth's true geography). By contrast,

Compass bearing In navigation, bearing or azimuth is the horizontal angle between the direction of an object and north or another object. The angle value can be specified in various angular units, such as degrees, mils, or grad. More specifically: * Absolu ...

s have a varying error factor at differing locations about the globe, and are less reliable than the compensated or true bearings. The measurement of relative bearings of fixed landmarks and other navigational aids is useful for the navigator because this information can be used on the

together with simple geometrical techniques to aid in determining the position of the vessel and/or its speed, course, etc. The measurement of relative bearings of other vessels and objects in movement is useful to the navigator in avoiding the danger of collision. For example: * The navigator on a ship observes a lighthouse when its relative bearing is 45° and again when it is 90°. He now knows that the distance from the ship to the lighthouse is equal to the distance travelled by the vessel between both observations. * The pilot of a boat observes that the relative bearing of another boat is less than 180° and decreasing (that is, it is now closer to dead ahead than before). He now knows he will pass astern of the other boat. If the bearing were to remain constant, the two boats would be on a collision course.

Examples

; Piloting : A bearing can be taken on another vessel to aid piloting. If the two vessels are travelling towards each other and the relative bearing remains the same over time, there is likelihood of collision and action needs to be taken by one or both vessels to prevent this from happening. ; Warfare A bearing can be taken to a fixed or moving object in order to target it with gunfire or missiles. This is mainly used by ground troops when planning on using an air-strike on the target. ; Search and rescue : A bearing can be taken to a person or vessel in distress in order to go to their aid.

Usages

There are several methods used to measure navigation bearings including: #In land navigation, a 'bearing' is ordinarily calculated in a

direction starting from a reference direction of 0° and increasing to 359.9 degrees.Keay, pp. 133-134 Measured in this way, a bearing is referred to as an ''

'' by the US Army but not by armies in other English speaking nations, which use the term bearing. If the reference direction is north (either true north, magnetic north, or grid north), the bearing is termed an ''absolute bearing''. In a contemporary land navigation context, true, magnetic, and grid bearings are always measured in this way, with true north, magnetic north, or grid north being 0° in a 360-degree system. #In aircraft navigation, an angle is normally measured from the aircraft's track or heading, in a clockwise direction. If the aircraft encounters a target that is not ahead of the aircraft and not on an identical track, then the angular bearing to that target is called a ''relative bearing''. #In marine navigation,

starboard Port and starboard are nautical terms for watercraft and aircraft, referring respectively to the left and right sides of the vessel, when aboard and facing the bow (front). Vessels with bilateral symmetry have left and right halves which ar ...

bearings are 'green' and

port A port is a maritime facility comprising one or more wharves or loading areas, where ships load and discharge cargo and passengers. Although usually situated on a sea coast or estuary, ports can also be found far inland, such as H ...

bearings are 'red'. Thus, in ship navigation, a target directly off the starboard side would be 'Green090' or 'G090'. This method is only used for a ''relative bearing''. A navigator on watch does not always have a corrected compass available with which to give an accurate bearing. If available, the bearing might not be numerate. Therefore, every forty-five degrees of direction from north on the compass was divided into four 'points'. Thus, 32 points of 11.25° each makes a circle of 360°. An object at 022.5° relative would be 'two points off the starboard bow', an object at 101.25° relative would be 'one point abaft the starboard beam' and an object at 213.75° relative would be 'three points on the port quarter'. This method is only used for a ''relative bearing''. #An informal method of measuring a ''relative bearing'' is by using the ' clock method'. In this method, the direction a vessel, aircraft or object is measured as if a clock face is laid over the vessel or aircraft, with the number twelve pointing forward. Something straight ahead is at 'twelve o'clock', while something directly off to the right is at 'three o'clock'. This method is only used for a relative bearing. #In land

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ...

, a bearing is the clockwise or counterclockwise angle between north or south and a direction. For example, bearings are recorded as N57°E, S51°E, S21°W, N87°W, or N15°W. In surveying, bearings can be referenced to true north, magnetic north, grid north (the Y axis of a map projection), or a previous map, which is often a historical magnetic north. #If navigating by gyrocompass, the reference direction is true north, in which case the terms '' true bearing'' and ''

geodetic bearing An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north. Mathematically, ...

'' are used. #In

stellar navigation Celestial navigation, also known as astronavigation, is the practice of position fixing using stars and other celestial bodies that enables a navigator to accurately determine their actual current physical position in space (or on the surface of ...

, the reference direction is that of the

North Star Polaris is a star in the northern circumpolar constellation of Ursa Minor. It is designated α Ursae Minoris ( Latinized to ''Alpha Ursae Minoris'') and is commonly called the North Star or Pole Star. With an apparent magnitude that ...

, Polaris. #In satellite broadcasting, a bearing is the combination of antenna

and

elevation The elevation of a geographic location is its height above or below a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface (see Geodetic datum § ...

required to point (aim) a satellite dish antenna in a given direction. The bearing for geostationary satellites is constant. The bearing for polar-orbiting satellites varies continuously. Polar bear bearing

Arcs

Moving from A to B along a great circle can be considered as always going in the same direction (the direction of B), but not in the sense of keeping the same bearing, which applies when following a rhumb line. Accordingly, the direction at A of B, expressed as a bearing, is not in general the opposite of the direction at B of A (when traveling on the great circle formed by A and B). For example, assume A and B in the northern hemisphere have the same latitude, and at A the direction to B is east-northeast. Then going from A to B, one arrives at B with the direction east-southeast, and conversely, the direction at B of A is west-northwest. Polar bears near the Pole

To "keep to a bearing" is not, in general, the same as going in a straight direction along a great circle. Conversely, one can keep to a great circle and the bearing may change. Thus the bearing of a straight path crossing the North Pole changes abruptly at the Pole from North to South. When travelling East or West, it is only on the Equator that one can keep East or West and be going straight (without the need to adjust). Anywhere else, maintaining latitude requires a change in direction, requires adjustment. This change in direction becomes increasingly negligible as one moves to a lower latitude

References

External links

Webpage with program to calculate Distance & Bearing

* ttp://www.freemaptools.com/range-finder.htm See the end point on a map when you specify a start point, a bearing and a distance.
More understandable definitions from an online classroom
{{DEFAULTSORT:Bearing (Navigation) Navigation Surveying