Exploring Surveying Types and Instruments

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

Measuring Tapes

Measuring tapes are made up of cotton, coated linen, or any other synthetic material. 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. Rarely used nowadays.
  • Metallic tape: Available in lengths 2, 5, 10, 20, 30, and 50 meters. Supplied in a leather or metal case with a winding device.
  • Steel tape: Available in lengths 1, 2, 10, 20, 30, and 50 meters. 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 and gives much more accurate measurements compared to tape. A chain is made up of connecting links of galvanized mild steel.

Some of the commonly used chains in surveying are:

  • Metric chain: 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.
  • 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 for accuracy, and adjustments are made if necessary.

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.

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.

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.

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.

Surveying Instruments Names 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