Azimuths and Bearings in Surveying: Definitions, Types, Methods, and Applications

What Is Azimuths Surveying?

Azimuths are defined as horizontal angles that are measured from the reference meridian in the clockwise direction. Azimuths are also called whole circle bearing systems (W.C.B). Azimuths are used in compass surveying, plane surveying, where it is generally measured from the north.

What Is Bearings Surveying?

In land surveying, a bearing is a clockwise or counterclockwise angle between north or south and a direction. 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.

Difference Between Azimuths and Bearings in Surveying

1. Azimuths Surveying Vs Bearings Surveying: Definitions

Azimuths Surveying: Azimuths are horizontal angles computed in a clockwise manner from the reference meridian.

Azimuths are often referred to as a whole circle bearing system (W.C.B). Azimuths are used in compass surveying and aircraft surveying and are typically measured from its north. Azimuths are obtained from the south in astronomical and the army.

Bearings Surveying: The bearing is the acute angle measured between the reference meridian and the given line.

The line is measured from north or south to east or west, yielding an angle less than 360 degrees. The angle is denoted by the letters N or S, followed by the angle value and the E or W direction.

2. Azimuths Surveying Vs Bearings Surveying: Types of Azimuth in Surveying

Azimuths Surveying: The azimuths may be geodetic, astronomic, inferred, recorded, or magnetic in nature, depending on the meridian adopted. It is often recommended to state the comparison meridian before beginning surveying actions to avoid future misunderstandings.

1. Policy Azimuths: For work-related purposes, azimuths must be interpreted to as north.
2. Astronomic Azimuths: A azimuth calculated from the astronomical pole in a manner perpendicular to the direction of gravitational at the observation point. Celestial measurements are used to calculate astronomic azimuths.
3. Geodetic Azimuths: A reference to the pole of a spheroid in a plane perpendicular to the spheroid at the start or end of a line. The Laplace correction can be used to calculate geodetic azimuths from astronomic azimuths. Imagine the minor adjustment required in an instrument to keep it levelled over a point if the plumb line is deflected to visualize the difference between astronomic and geodetic azimuths (deflection of the vertical). This minor adjustment will result in a correspondingly minor change in the measured angle.
4. Grid Azimuths: The angle in the plan projection between grid north and the straight line from the point of observation to the point observed is known as the grid azimuth. Only when the point of observation is on the central meridian is grid azimuth the same as geodetic azimuth.

Bearings Surveying: Bearing of a line is its direction comparative to a specified meridian.

1. True Meridian: The true meridian along a line is defined as a line in which a plane aligns the earth’s surface after passing via the true north as well as south extremes As a result, it traverses the true north as well as the south.  Astronomical studies can be used to determine the true meridian’s path via a point.
   • True Bearing: it is a line that is in horizontal angle formed by this with the true meridian through those line’s poles. The true bearing of a line is a consistent amount because the path of the true meridian via a point remains intact.
2. Magnetic Meridian: A magnetic bearing is measured from a suitable magnetic meridian, a grid bearing from a suitable grid meridian, inferred bearings from a suitable arbitrary meridian, a geodetic bearing from a geodetic meridian, and an astronomic bearing from an astronomic meridian. Observing the needle of the compass yields the magnetic meridian.
   • Magnetic Bearing: The magnetic bearing of a line is the horizontal angle formed by the magnetic meridian passing through one of the line’s extremities. It is measured with a magnetic compass.
3. Arbitrary meridian: Any convenient direction towards a permanent and important mark or signals, such as a church spire or the top of a chimney, is an arbitrary meridian. These meridians are used to calculate the relative positions of lines in a small area.
   • Arbitrary Bearing: The horizontal angle formed by a line with any arbitrary meridian passing through one of its extremities. It is measured using a theodolite or sextant.

Azimuths Surveying Vs Bearings Surveying: Method of Correcting

Azimuths Surveying: Method of correcting the azimuth in surveying.

A technique for correcting an electronic compass’s azimuth error is revealed.

1. While spinning the electronic compass 360 degrees, measure a declination value corresponding to a predetermined azimuth angle.
2. Use a sine function to fit the measured declination value.
3. Demonstrate a sinusoidal function.
4. Applying offset, amplitude, and azimuth corrections to the displayed sinusoidal function.

Bearings Surveying: Method of correcting the bearing in surveying.

There are two methods of correcting the bearing affected by local attraction:

1. Included Angle Method: The traverse’s incorporated angles being determined at first, trailed by the traverse’s right bearings, that are determined to use the included angles again starting from the line that is unaltered by neighborhood fascination.
2. Error Computation Method: At each survey station, the direction and amount of local attractions are determined. Beginning with a line that is not influenced by local attraction, the corrected bearing of the traverse is calculated. This method is more precise than the included angle method. It is used by the majority of surveyors.

Azimuths Surveying Vs Bearings Surveying: Applications

Azimuths Surveying: Azimuth applications in surveying.

1. Azimuth is used in boundary, control, and topographic surveys, among other things.
2. Azimuths are used in compass and aircraft surveying.

Bearings Surveying:

1. A ‘bearing’ is normally calculated in a clockwise direction starting from a reference direction of 0° and increasing to 359.9 degrees in land navigation.
2. In aircraft navigation, an angle is commonly measured clockwise from the aircraft’s track or heading.
3. In naval navigation, starboard bearings are referred to as ‘green,’ while port bearings are referred to as ‘red.

Azimuths Surveying Vs Bearings Surveying: Forward and Back

Azimuths Surveying: Forward and Back Azimuths

1. The forward azimuth of the line along whereby the poll is being conducted is the forward azimuth, as well as the reversing azimuth is the backward azimuth. Throughout the instance of azimuth, the values for forwarding and backward azimuth would be varied. The backward and forward azimuths can be measured by multiplying or deducting 180°.
2. If the forward azimuth is much less than 180°, the backward azimuth is calculated by adding 180° to the forward azimuth. If the forward azimuth is larger than 180°, deduct 180° to get the backward azimuth.
3. Forward azimuth indicates the line’s forward direction, and backward azimuth indicates the line’s backward direction. By adding or subtracting 180 degrees, the forward azimuth may be shifted to the back azimuth.
4. If line AB has a forward azimuth of 70 degrees, then the backward azimuth would be 70 + 180 = 250 degrees. If the line AD’s azimuth is 230 degrees, the backward azimuth is 230 – 180 = 50 degrees.

Bearings Surveying: Forward and Back Bearings

1. The forward bearing of a line is the bearing of a line in the direction in which a survey is advancing. Back bearing refers to the bearing of the line in the opposite direction of progress. Forward bearings can be converted to back bearings and vice versa in aircraft surveying.
2. Both the forward and back bearing values will be the same, but the direction will be opposite. The direction will shift from N or S to S or N, and from E or W to W or E

Computation of Azimuths and Bearing in Surveying

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Designations of Azimuth and Bearings in Surveying

1. Back Bearing (BB): Backward Bearing refers to bearings measuring in the opposite way of surveying progress, namely in the backward direction of the survey line.
2. Fore Bearing (FB): Bearings measured when surveying, i.e. in the forward direction of survey lines, are referred to as fore bearings or forward bearings.
3. Calculated Bearing: The bearings computed from field observations are referred to as calculated bearings.
4. Observed Bearing: The bearings taken in the field with an instrument are referred to as Observed Bearings.
5. Whole Circle Bearing: Bearings measured clockwise from the north are referred to as full circle bearings. The value ranges between 0 and 360 degrees. Bearings measured from the north or south towards the east or west, whichever is closer, are known as diminished bearings. For each quadrant, the values range from 0 to 90 degrees. It is often referred to as quadrantal bearing (QB).

Frequently asked questions (FAQs) that could be included in the article about azimuths and bearings in surveying:

What is the difference between azimuths and bearings in surveying?

Azimuths are horizontal angles measured clockwise from a reference meridian, typically from north. Bearings, on the other hand, are angles measured clockwise or counterclockwise from north or south to a direction east or west.

How are azimuths and bearings used differently in surveying?

Azimuths are commonly used in compass and aircraft surveying, while bearings are crucial for determining the direction of survey lines relative to a specified meridian.

What are the types of azimuths used in surveying?

Azimuths can be geodetic, astronomic, magnetic, and grid, depending on the reference meridian chosen for measurement.

What are the types of bearings used in surveying?

Bearings include true bearings (relative to true north), magnetic bearings (relative to magnetic north), grid bearings (relative to grid north), and arbitrary bearings (relative to a chosen arbitrary direction).

How do surveyors correct azimuths and bearings for accuracy?

Azimuths can be corrected by adjusting for declination errors using methods such as electronic compass calibration. Bearings are corrected by accounting for local magnetic attractions or using included angle or error computation methods.

What are forward and back azimuths/bearings in surveying?

Forward azimuths/bearings indicate the direction of a survey line’s progression, while back azimuths/bearings indicate the opposite direction. They can be calculated by adding or subtracting 180 degrees from the forward azimuth/bearing.

In what applications are azimuths and bearings commonly used in surveying?

Azimuths are essential for boundary, control, and topographic surveys, as well as in navigation and orientation in aircraft. Bearings are crucial for land navigation, boundary marking, and aligning structures relative to a map projection’s grid.

How do azimuths and bearings relate to each other in practical surveying tasks?

Azimuths provide a continuous measurement around a full circle, while bearings are typically measured within a quadrant (0 to 90 degrees) relative to cardinal directions.

What are whole circle bearings (WCB) and quadrantal bearings (QB)?

Whole circle bearings refer to measurements from 0 to 360 degrees clockwise from north, covering a full circle. Quadrantal bearings refer to bearings measured from north or south towards east or west within each quadrant of a circle.

Why is understanding azimuths and bearings important in modern surveying practices?

Azimuths and bearings provide essential directional information for accurate mapping, navigation, construction alignment, and legal boundary establishment in various fields of surveying and engineering.