Compass Surveying: Measuring Directions and Angles with a Prismatic Compass, Lecture notes of Survey Sampling Techniques

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B. Tech. IV Semester (Civil Engineering)

CE: 14102 – SURVEYING

Unit-II: Measurement of Direction and Angle, Traversing

(Part-I: Measurement of Direction)

Unit-II: Measurement of Direction and Angle, Traversing

Syllabus

➢ Designation of Bearings and inter-conversion, ➢ Included angles from bearings and vice versa, ➢ Magnetic declination, local attraction, ➢ Temporary adjustments and parts of prismatic compass; ➢ Vernier Theodolite, measurement of horizontal angles: repetition method & reiteration method, traversing by compass and theodolite, computations of traverse coordinates, traverse adjustment; Total Station

Compass Surveying

Compass Surveying is the branch of Surveying in which directions of all the survey lines are determined with a compass and the length of the survey lines are measured with a tape. ✓ In practice, Compass Survey is generally used to run a traverse. ✓ In a traverse, framework consists of a series of connected survey lines to form an open or closed polygon. ➢ When the lines form a framework which ends at the starting point, it is known as a closed traverse. ➢ If the framework ends elsewhere, it is said to be an open traverse.

Compass Surveying

Location of a Point by Distance and Direction The direction of a line is defined by a horizontal angle with respect to a reference line. ✓ This reference line is known as Meridian. ✓ The horizontal angle measured with respect to reference line (i.e. meridian) is termed as Bearing. In relative direction, the reference line does not remain fixed over a period of time.

Meridians and Bearings

1. Magnetic Meridians : Magnetic Bearing

2. True Meridian : True Bearing

3. Arbitrary Meridian : Arbitrary Bearing

Meridians

The reference line with respect

to which horizontal angle of a

survey line is measured is called

as meridian.

1. True Meridian

✓ True Meridian through a point is the great circle passing through the point, geographical North and South poles. ✓ Thus, true meridian may be considered as a plane passing through the point on the surface of Earth and containing the axis of rotation of the earth. ✓ The direction of true meridian through a point is established by astronomical observations. ✓ The true meridian does not change with time.

Bearings

Bearing of a line is its direction measured with reference to a given meridian.

Three types of Bearings:

1. True Bearing

2. Magnetic Bearing

3. Arbitrary Bearing

✓ True Bearing or Azimuth of a line is its horizontal angle from the true meridian, i.e. Geographical North. ✓ Arbitrary Bearing of a line is the horizontal angle which it makes with any arbitrary meridian ✓ The horizontal angle which a line makes with the magnetic meridian is called Magnetic Bearing.

Designation of Bearings

Inter-conversion

Designation of Bearings

RB / QB : Reduced Bearing or Quadrantal Bearing System

WCB & RB Systems Represented Together

Inter-conversion: RB to WCB

Fore Bearing & Back Bearing

FB & BB

Thanks to all of You Any Questions!