What does surveying mean?
Surveying is the practice that determines the relative three-dimensional positions of many different points on the earth’s surface. There are various instruments used in Surveying like Theodolites, Total station, Tripod stands, Plane table, etc. for measuring horizontal angle, vertical and sloping angle, which are very useful for giving accurate and precise measurement.
Instruments used for on-field linear surveying
The measuring tapes are made of foldable fabric, cotton, or any synthetic material and are marked with usual centimeters, feet, etc. They are available in 20, 30, or 50 meters in length. Linen or cloth tapes come in a range of 10, 20, 25, or 30 meters where a ring made of brass is fixed at the far end. These tapes are scarcely used in today’s times. Metallic tapes have small rings fastened at the terminal edges used for protection. Steel tapes are packed in corrosion-proof cases and a winding device with the best quality assurance and precise readings, but the surveyor must be handled with care. Invar tapes come in 20, 30, or even 100 meters in length and are made from nickel and steel alloys having a low thermal coefficient of expansion. Again, they give accurate measurements but are delicate instruments.
They are required for the measurement of distances on the surface of the earth, which are more precise than tapes and are kept in a position for readings. Chains contain links that are connected made up of galvanized mild steel. Each connecting link is 20 cm in length. Tally mark of 5 meters given sometimes are marked on the chains. The total chain length is 20 to 30 meters inclusive of a brass handle on each end along with swivel joints for easy turning without any twisting. Examples are the Metric chain, Surveyor’s chain, Engineer’s chain, and Revenue chain.
The surveyor uses arrows to mark lengths of chain on the ground, it is placed at the far end of the chain and made up of tempered and hardened wire (steel). One edge of the arrow sharpened and the other bent into a loop.
Timber made peg is used by the surveyor to mark points on the ground’s surface. With tampering ends, a hammer is required to insert the peg into the ground.
Ranging rods and Off-set rods
Length being 2 or 3 meters, they are colored with alternate strips of either a combination of white and black or red and white simultaneously and each kept at 20 cm of length. They are made of well-seasoned timber with circular or octagonal cross-sections. Off-set Rods are used for measuring rough points or offsets similar to Ranging Rods.
The surveyor uses it to locate the center of instruments like a theodolite, transit-theodolite, plane table, etc. For Ground Surveying, it transfers the points on the ground while chaining on sloping terrain and also make ranging poles at a 90-degree angle.
Instruments used for setting out right angles
One of the simplest instruments for laying out right angles (horizontal as well as vertical), it comprises of a frame with two pairs of slits opposite to each other on a pole. Three types of cross-staff include open cross-staff, French cross-staff, and Adjustable cross-staff.
Optical and Prism Square
Accuracy wise better than cross-staff which is set on line whose perpendicular needs to be found. It contains 3 slits with circular boxes out of which the two-point out at the Ranging Rod at the edge of the line. One more rod is placed in such a way that at one point two images meet each other which is on the perpendicular of the previous line. Prism square works on similar grounds but is more precise than optical square.
Instruments used for setting out directions
It is magnetic and the surveyor uses it to measure the magnetic meridian. Portable and convenient, it can be either placed on a palm or fixed on a tripod stand. South end at 0°, North end at 180°, East end at 270°, and West end at 90°. Some temporary adjustments are to be made every time, before re-using the compass.
The ring which has graduated markings on it is attached to the compass box directly which becomes easier for the surveyor to locate the directions. The needle has Magnetic Locators, floats freely and the line of sight coincides with the magnetic meridian, N and S are at 0° and E and W at 90° respectively.
Instruments used for setting out angles
A theodolite being the most accurate instrument used by a surveyor for measuring both horizontal and vertical angles, it is extensively used nowadays. The non-transit theodolite has become outdated and transit theodolite is used for measuring the transit level.
Parts used in Theodolite are Telescope, Tripod stand, Vertical circle, Vertical plane, Index/Vernier frame, Standards/A frame, Levelling head, Two spindles, Lower/Scale plate, Upper/Vernier plate, Plate levels, Tripod, Plumb bob, Compass, and Striding level.
Setting up theodolite requires leveling and parallax error elimination. Placing the bob for center location and leveling using a screw head. Tribrachs are attached at the lower end which is replaceable.
Total station (Electronic Transit Theodolite)
Total Station is similar to a theodolite but a total station consists of an electronic distance meter (EDM). The alignment of crosshairs on the reflector is to be aligned to the rod the angles are measured with sloping distances respectively. Total Station can also store the readings which is a built-in function and can be later uploaded on other devices. A Total Station is used to take horizontal, vertical, and slope distances. A Tripod stand is used to support the Total Station. Modern Total Station can not only store data but that data can be used for data analysis of various reading records.
Instruments used in plane table surveying
The plane table surveying comprises an alidade (Plain and Telescopic), plumbing fork, spirit level, trough compass, and drawing paper. Alidade is an equipment to sight an object that uses LOS (Line of Sight) to perform a certain task.
Instruments used for direct levelling
The telescope is attached firmly to the two collars which can be fixed by adjusting the screws of the spindle. The clamp screw regulates the movement of the spindle along the vertical axis and the tangent screw is used for accurate motion.
Others include Wye/Y level, Reversible level, Tilting level, Auto or Automatic level, Instrument level and Laser level.
It is a linear rod with marks from 0 and helps for the measurement of distances between LOS (Line of Sight) and station
Other types are Self-reading staff, Solid staff, Folding staff, Telescopic staff, and Target staff.
Context and Applications
The topic is taught in courses such as:
- Bachelors in Technology (Architecture)
- Bachelors in Technology (Civil Engineering)
- Bachelors in Technology (Remote Sensing)
- Masters in Science (Geospatial Systems)
1. What are Invar tapes made up of?
- Nickel and Steel alloy
- Bronze and Gold
- Aluminum alloy
- None of these
Correct option- a
Explanation: Invar tapes are made up of Nickel and Steel alloy.
2. At what meters of distance, the tally marks are sometimes given on the Surveying Chains?
Correct option- d
Explanation: At 5 meters of distance, the tally marks are sometimes given on the Surveying Chains.
3. Color coding of alternate bands on the Ranging Rods are?
- White and Black
- Red and White
- Both of these
- None of these
Correct option- c
Explanation: Color coding of alternate bands on the Ranging Rods are White and Black and Red and White.
4. Which of the following instrument is used for setting out directions?
- Optical and Prism Square
- Prismatic compass
- Leveling staff
Correct option- b
Explanation: Prismatic compass instrument is used for setting out directions.
5. Which of the following instruments is used in leveling?
- A Self-reading Staff
- Surveying Staff
- Ranging Rod
- An alidade
Correct option: a
Explanation: A self-reading Staff instrument is used in Levelling.
- Geographic Information Systems
- Spatial Computing
- Civil Engineering
- Mapping and Remote sensing
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