23 Surveying Instruments And Their Uses

Surveying is the process of measuring and mapping the physical features of a piece of land or property. This can include measuring distances, angles, and elevations. To create detailed maps and plans that can be used for a variety of purposes, such as land development, construction, and resource management.

Surveying is an essential component of many industries, from engineering and architecture to agriculture and environmental science. The field of surveying has evolved significantly over time, with advances in technology and new methods of data collection and analysis.

In this article, we will explore the different types of surveying and their uses in the field, and the importance of accurate surveying for a variety of industries.

Surveying Instruments

The following are surveying instruments and their uses,

Measuring Tapes

It is made up of cotton, coated linen, or any other synthetic material. Centimeters or decimeters are marked on the tape. They are available in lengths of 20, 30, or 50 meters.

Some of the commonly used tapes in surveying are:

Cloth/linen tape: Available in lengths 10, 20, 25, and 30 meters. Also available in lengths of 33, 50, 66, and 100 feet. A brass ring is provided at the terminal end of this tape. Rarely used nowadays.

Metallic tape: Available in lengths 2, 5, 10, 20, 30, and 50 meters. Except for 2 and 5-meter tapes, other tapes have a small ring fastened at the ends which is of the same width as that of the tape for protection and are supplied in a leather or metal case with a winding device.

Steel tape: Available in lengths 1, 2, 10, 20, 30, and 50 meters. Except for 1 and 2-meter tapes, other tapes have a small brass ring fastened at the ends. These tapes are supplied in a corrosion-resistant metal case or a leather case with a winding device.

Surveying Chains

The chain is used to measure the distance on the ground. It gives much more accurate measurements as compared to tape. A chain is a surveying instrument that is made up of connecting links of galvanized mild steel. The mild steel wire is bent into a ring and joined to each other with three small circular or oval rings. Each connecting link measures 20 cm.

A tally marker or a special joint is also installed sometimes to mark the distance of 5 meters. The total length of the chain is 20 meters or 30 meters, which also includes a brass handle on each end. The handles are provided with swivel joints so they can be easily turned during surveying without being twisted.

Some of the commonly used chains in surveying are

Metric chain- Widely used and available in lengths of 5, 10, 20, and 30 meters.
Surveyor’s chain: Length is 66 feet and has 100 links Widely used for land measurement as 10 square chains make 1 acre.
Engineer’s chain: Length is 100 feet and has 100 links. Brass tags are installed every 10 feet.
Revenue chain: Length is 33 feet and has 16 links.

A chain has to be tested if it is accurate and if necessary adjustments are made if not.

Arrow

Arrows are used for marking and are made up of hardened, and tempered steel wire of good quality. 10 arrows are usually sold with a chain. Its length is about 25-50 cm. One of its ends is sharpened while the other end is bent into a circular loop.

To mark the chain length on the ground, an arrow is inserted at the end of the chain.

Peg

Pegs are mostly made of timber. They are also used to mark out the locations on the ground at terminal points or the end of the survey line. They are 2.5-3 square centimeters and are of 15-centimeter length with a tapered end. A hammer is used to drive the peg into the ground.

Ranging Rods

Ranging rods are 2-3 meters in length and are painted with alternate bands of two colors like white and black, red and white in succession. Each band is kept at a length of 20 centimeters. Ranging rods are made of well-seasoned timber. Their cross-section is kept either circular or octagonal with a 3 cm nominal diameter.

They are used to range an intermediate point on a survey line. A red, yellow, or white flag is tied at its top while carrying out longer surveys because the rod is not visible beyond a 200-meter distance.

Offset Rods

It is similar to a ranging rod but is of a 3-meter length. They are also wooden rods, circular in cross-section. Its one end is pointed with an iron shoe and at the other, a notch or hook is provided.

It is used to take rough offsets in the nearby regions. Also, the right angles can be set out with its help as it has two narrow slots at its center.

Plumb Bob

It is used to transfer the points to the ground on a slope while chaining. It is also used to make the ranging poles vertical. In theodolites, compasses, plane tables, and other surveying instruments, it is used for centering purposes.

Cross Staff

It is the simplest instrument for setting out right angles on a survey line. It has a frame containing two pairs of opposite slits mounted on a pole. The pole can be used to fix the instrument on the ground.

Cross Staff has three types

Open cross-staff: Two pairs of vertical slits are present which gives two lines of sight at right angles.

French cross-staff: It has a hollow octagonal box set up on a pole. On each face, vertical slits are cut in the middle for sighting. The lines of sight are at an angle of 45° to one another.

Adjustable cross-staff: It has two cylinders of equal diameter with sighting slits placed on each other. The upper box can be rotated and is provided with a vernier to take measurements. The lower box has graduations of degrees and subdivisions. Any angle can be set out with the help of this instrument.

Optical Square

It is more accurate than a cross-staff. Also, it is convenient to use for setting out right angles. It has a circular box with three slits. The instrument is set on the line whose perpendicular is to be set out. Two slits point towards the ranging rod at the end of the survey line.

Then another ranging rod is to be set at such a point that the two images coincide with each other. This point is perpendicular to the initial line.

Prism Square

The principle of the prism square is similar to that of the optical square. However, it is more precise as compared to the optical square. It can be used in a similar manner as an optical square. Unlike the optical square, adjustment is not required, as the angle between the reflecting surfaces does not vary.

Site Square

It has a cylindrical metal case and two telescopes fixed at 90°. It is used to set out offset lines at right angles.

Note: When the direction is established with respect to each other, it is called an angle. If the direction is established with respect to a meridian, it is called bearing.

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It comprises a magnetic needle attached to a graduated circular ring made up of aluminum. The needle orients itself to the magnetic meridian if it is on the pivot. Object vane and eye slit are attached to the compass box and help in locating the line of sight.

It is a magnetic compass that measures the magnetic meridian. It is portable and hence convenient too. It can be either used in the palm or fixed on a tripod.

The object vane has thin vertical hair while the eye slit has a vertical slit. A triangular prism is also attached below the eye slit to suit different sighting requirements with both horizontal and vertical faces convex. The south end corresponds to 0° while the west end corresponds to 90° and so on. Thus, the north end is at 180° while the east end is at 270°.

Temporary or permanent adjustments are to be carried out for the compass as required. Centering, leveling, and focusing of the prism are temporary adjustments. The temporary adjustments are to be made every time the instrument is set.

Surveyor’s Compass

The graduated ring is directly attached to the box instead of the needle in the surveyor’s compass. The needle is allowed to float freely over the pivot, but it does not orient itself to the magnetic meridian as in the case of a prismatic compass.

The object vane and eye vane are similar to that of the prismatic compass, however, no prism is provided. The instrument is to be fixed on a tripod.

The readings through this compass are taken against the north end of the needle by looking through the top glass vertically. When the line of sight coincides magnetic meridian, the north and south ends are at 0°. While the east and west end corresponds to 90°.

Temporary or permanent adjustments are to be carried out for the compass as required. Centering and leveling are temporary adjustments. The temporary adjustments are to be made every time the instrument is set.

Theodolite

It is the most precise instrument for the measurement of horizontal and vertical angles. It is popular in various surveying applications. There are two types of theodolite- transit, and non-transit. non-transit theodolites have become obsolete these days.

Transit theodolite is such theodolite in which the telescope can be revolved by 180° in the vertical plane.

Parts of transit theodolite include

Telescope
Vertical circle
Index/Vernier frame
Standards/A frame
Leveling head
Two Spindles
Lower/Scale Plate
Upper/Vernier Plate
Plate levels
Tripod
Plumb bob
Compass
Striding level

Temporary adjustments of a theodolite include setting over the station, leveling, and elimination of parallax. Setting up includes centering with a plumb bob and approximate leveling. Leveling up is done by the screw head- it is either a three-screw head or four screw head. Parallax is eliminated by focusing on the eyepiece as well as the objective.

A theodolite can be used to,

Measure the magnetic bearing of a line
Measure direct angles
Measure deflection angles
Extend a straight line
Establish a straight line between two points
Locating the point of intersection between two straight lines
Setting out a horizontal angle
Setting out an angle by repetition
Establish grade
Measure the difference in elevation
Setting out curves

Repetition methods or Reiteration methods can be employed for setting out horizontal angles to obtain more precise results.

Total Station

It is an electronic transit theodolite with an electronic distance meter (EDM).

The crosshairs on the reflector of TS are aligned to the ranging rod and the vertical and horizontal angles are measured along with slope distances simultaneously.

It is used to take the measurement of-

Horizontal angles: The rotation of the optical axis of TS from the instrument north in a horizontal plane gives the horizontal angle.
Vertical angle: The inclination of the optical axis of TS from the local vertical gives a vertical angle.
Slope distance: The distance between TS and the target gives the slope distance.

TS can store data too as some have inbuilt internal electronic data storage, which can be uploaded to the computer, and the data analysis can be done with the help of various applications.

A tripod with a device for leveling and controlling its orientation is used in plane table surveying.

Plane Table

Three types of plane tables are commonly used,

Traverse table: It consists of a small drawing board mounted on a light tripod so that the board can be rotated about the vertical axis and then clamped in the desired position. The table is leveled via tripod legs by eye estimation.

Johnson table: It consists of a drawing board of size 45 * 60 cm or 60 * 75 cm. The head has a ball and socket joint while on its underside, a vertical spindle with thumbscrews is present.

After loosening the upper screw, the table can be tilted via the ball and socket joint and the leveling is done. Then the clamp is tightened so that the board is fixed in the horizontal position. The lower screw is loosened to fix the orientation of the table by moving it about the vertical axis.

Coast Survey table: This survey table is used for high-precision works and is more accurate than the previous two. There are three-foot screws for accurate leveling. A clamp and tangent screw is also provided for moving the table about the vertical axis.

Plumbing Fork

It is used for centering in large-scale works at the station point. It is composed of a hairpin-shaped light metal frame with arms of equal length. A plumb bob is suspended from the lower arm.

It is also used for transforming the ground point on the sheet at the beginning of the survey so that the plotted point and ground station are in the same vertical line.

The upper arm is set on the table while the plumb bob on the lower arm corresponds to the ground point.

Spirit Level

It is used to ensure that the table is leveled properly. The spirit level is placed at two perpendicular positions to ascertain that it is leveled.

It is either of tubular or circular type. Its base is flat so that it can be easily placed on the table. The table is leveled if the bubble is at the center.

Trough Compass

It is used for the orientation of the plane table towards the magnetic north.

In plane table surveying, a trough compass is used in which the longer sides of the compass are flat and parallel. The sides can be used as rulers or can be used to coincide with a line already drawn on the paper.

Drawing Paper

A superior quality drawing paper is used that has a minimum effect on the humidity of the atmosphere. Otherwise, the scale is disturbed.

Fiberglass sheets or paper with a backing of aluminum are used for high-precision works.

Level

It is used to provide a horizontal line of sight. A horizontal line can be established with the help of a level. It is the line perpendicular to the plumb line.

The telescope, level tube, leveling head, and tripod are the main parts present on every level.

Differential leveling, profile leveling, cross-sectioning, reciprocal leveling, and precise leveling are some of the methods of precise leveling that can be carried out by a level.

Temporary adjustments of station adjustments are to be made each time the level is set up including setting up the level, leveling up, and eliminating parallax.

There are four types of levels:

Dumpy level

At this level, a telescope is firmly attached to two collars, which can be fixed by adjusting screws carried by a vertical spindle.

The movement of the spindle about the vertical axis is regulated by a clamp screw. A tangent screw is used for precise movements. Two parallel plates are fixed on either three or four-foot screws in leveling head.

Leveling Staff

It is a straight rod with graduation marks with a zero from the bottom. It helps in determining how much above or below the station from the line of sight.

There are two types of leveling staff- self-reading staff and target staff.

Self-reading staff: It can be read directly by the instrument man. The readings are always taken from the telescope and hence appear inverted. Therefore, readings are taken downwards.
Solid Staff- The smallest division is 5 mm. its length is about 3 meters.
Folding Staff- Its length is 10 feet and it is hinged in the middle. It can be folded about the hinge when not in use for convenience.
Telescopic Staff- It has three telescopic lengths of 1.5, 1.5, and 2 meters when stretched out fully. Normally, its total length is 5 meters. A circular bubble is also installed at the back in a suitable case.
Target staff: It has a moving target against which readings are taken by the staff man. The sliding target comes along with the vernier.

Surveying Instruments Names And Their Uses

Following are different surveying equipment and their uses

Sr. No.	Instrument	Uses
1.	Measuring tape	To measure linear distances
2.	Chain	To measure linear distances with precision
3.	Arrow	To mark a single chain distance
4.	Peg	To fix points on the ground To mark the terminal points of survey lines on the ground
5.	Ranging rods	To mark the position of stations To sight the stations To range straight lines
6.	Plumb bob	To establish a vertical line
7.	Cross Staff	To set out a right angle from a survey line
8.	Optical Staff	To set out a right angle from a survey line
9.	Prism Square	To set out a right angle from a survey line
10.	Site Square	To set out a right angle from a survey line
11.	Prismatic Compass	To find the bearing of traversing To find included angles
12.	Surveyor’s Compass	To find a bearing and angles between two survey lines in a traverse
13.	Level	To establish relative heights of points with the help of leveling staff
14.	Leveling Staff	To determine the height difference between two points To measure the height or depth of a point with respect to the datum
15.	Theodolite	To measure the angle between two pre-decided visible points in either a horizontal or vertical plane.
16.	Total Station	To measure horizontal angle To measure vertical angle To measure slope distance
17.	Tripod	To support surveying instruments like a compass, level, theodolite, or total station
18.	Plane table	To provide a solid and level surface to make field drawings
19.	Alidade	To sight a distant object and establish a line of sight in a plane table surveying
20.	Plumbing fork	For centering of alidade in plane table surveying
21.	Spirit Level	To level the table in plane table surveying
22.	Trough Compass	To set the orientation towards magnetic north in plane table surveying
23.	Drawing Paper	To note field points on paper in a plane table surveying

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23 Surveying Instruments and Their Uses