Theodolite Surveying

Theodolite is a surveying instrument. It is very popular in measuring horizontal and vertical angles. There are different types of theodolite available in the market. To fulfill the purpose of a specific one must choose the right type of theodolite for the surveying. Different theodolite types are discussed in the following segments.

Types of Theodolite

There are various kinds of theodolites for different purposes of different constructional works. Usually, four types of theodolites are uses in site works for different measuring points. Such as-

  1. Repeating Theodolite
  2. Directional Theodolite
  3. Electrical Digital Theodolite
  4. Total Station
To clearly saying, theodolites can be also classified into two types
  1. Primary Theodolite
  2. Electronic Digital Theodolite
Theodolite Classification 1
This classification of theodolite contains four types of theodolite which are discussed below.
Repeating Theodolite
This design facilitates horizontal angles to be remade any number of times and added directly on the instrument circles. This type of instruments is restricted for locations where
  • the support is not steady, or
  • area for using other such instruments is limited.
Directional Theodolite
Angles are obtained by deducting the first direction reading from the second direction reading. This reads directions rather than angles. The non-repeating instrument has no minor motion.
Electrical Digital Theodolite
Naturally interprets and records horizontal and vertical angles. Eliminates the standard reading of scales on graduated circles
Total Station
The total Station accommodates the functions of a theodolite for measuring angles, an EDM for measuring gaps, digital data, and information documentation. Examples of Total Stations are the Nikon DTM 801, Topcon, and Geodimeter 400 series.
Theodolite Classification 2This classification of theodolite contains two types of theodolite which are discussed below.
Primary Theodolite
Primary Theodolite can be two types.
  1. Transit Theodolites: A theodolite is named a transit theodolite once its telescope will be transited i.e. rotated through a whole revolution regarding its horizontal axis within the vertical plane.
  2. Non-Transit Theodolite In this kind, the telescope cannot be transited. They are inferior in utility and have currently become obsolete.
Electronic Digital Theodolite
This type of theodolite provides the worth of observation directly within the viewing panel. The exactitude of this sort of instrument varies within the order of 1" to 10". It has also two types.
  1. Vernier Theodolites: For reading the graduated circle, verniers are used to correct reading of measuring points and this theodolite is termed as a Vernier theodolite.
  2. Micrometer Theodolites: A micrometer provides to browse the graduated circle identical be termed as a Micrometer theodolite.
This Digital theodolite is also known as Modern Theodolite and can perform the following functions:
  • Distance measurement
  • Angular measurement
  • Data processing
  • Digital display of point details
  • Storing data is an electronic field book
Parts of a Theodolite
Knowing the parts of a theodolite is important. The parts should be accustomed to each other. Without regulate of the parts cannot be worked accurately. Whenever theodolite uses in sites, each part takes seriously. Depends on placing the parts, measuring result could be changed or stabled. Theodolite consists of some main parts, such as:
  • Telescope
  • Horizontal plate (Circle)
  • Vertical Circle
  • Index frame
  • The standards
  • The upper plate
  • The lower pale
  • Plate level
  • The leveling head
  • The shifting head
  • Magnetic compass
  • Tripod
  • Plumb bob
These theodolite parts are discussed briefly below.
  • Telescope- It is used to see the object. It rotates about a horizontal axis in the vertical plane. It can be up to an accuracy of 20 degrees.
  • Horizontal plate (Circle)- It is used for measuring the horizontal angle.
  • Vertical Circle- It is used for measuring the vertical angle.
  • Index frame- The frame consists of horizontal and vertical wings. This frame is additionally called t-frame or vernier frame. The horizontal wing helps to require the measurement of vertical angles and vertical wing helps to grip the telescope at the wanted level.
  • The standards- Standards look like 'A' shaped and for that, it is known as A-frame. The standards’ frames support the telescope and allow it to spin about the vertical axis.
  • The upper plate- It is the bottom on that standard and vertical settled. It also helps to rotate the standards and telescope in a regular manner for correct measurement. it is necessary that the upper plate should be horizontal to the alidade axis and coordinate to the trunnion axis. The instrument must be leveled and this leveled is achieved by adjustment of three-foot screws and perceptive an explicit tube bubble. The bubble is understood as plate bubble and located within the upper plate.
  • The lower plate- The lower plate is that the base of the entire instrument. It homes the foot screws and the carrying for the vertical axis. it is strictly connected to the tripod-escalating assembly and does not modification or shift. Horizontal angles are measured with this plate.
  • Plate level- Plate levels are lifting by the upper plate that is the proper angles to every different with one they are coordinate to trunnion axis. Plate levels facilitate the telescope to mend incorrect vertical point.
  • The leveling head- The leveling head consists of two parallel triangular plates called tribrach plates. The upper one is called as upper tribrach plate and is used to level the upper plate and telescope with the help of equalizing screws provided at its three ends. The lower one is called a lower tribrach plate and is connected to the tripod stand.
  • The shifting head-Shifting head conjointly consists of two parallel plates that are modified one over the opposite among a limited range. Shifting head lies below the lower plate. It is helpful to centralize the complete instrument over the positioning.
  • Magnetic compass- A circular box compass or magnetic compass is mounted on the vernier scale between the standards. It is provided for taking the magnetic bearing points.
  • Tripod- The theodolite is mounted on a powerful tripod once getting used within the field. The tripod’s legs are sturdy or framed. At the lower ends of the legs, pointed steel shoes are provided to urge them pushed into the bottom. The tripod head has male screws on that the trivet of the leveling head is screwed.
  • Plumb bob- To center the instrument precisely over a station mark, a plumb bob is suspended from the hook fitted to the rock bottom of the central vertical axis.
The theodolite has other more parts are - Level tube, Foot Plate, Standard Frame, Upper Clamp, Trunnion Axis, Lower Clamp, Vernier Frame, Inner Axis, Outer Axis, Altitude Level, Leveling Screw, Clamp Screw. Tangent Screw.
Uses of Theodolite in Surveying

Theodolite uses for many purposes, but mainly it is used for measuring angles, scaling points of constructional works. For example, to determine highway points, huge buildings’ escalating edges theodolites are used. Depending on the job nature and the accuracy required, theodolite produces more curved of readings, using paradoxical faces and swings or different positions for perfect measuring survey.

Followings are the major uses of theodolite:
  • Measuring horizontal and vertical angles
  • Locating points on a line
  • Finding the difference in the level
  • Prolonging survey lines
  • Ranging curves
  • Setting out grades
  • Tachometric surveying
The theodolite helps us a good within the engineering field. This instrument plays a major role in measurement horizontal angles, vertical angles, bearing, etc. To use theodolite, it is necessary to know about theodolite parts, types of theodolite and for what it is used wisely in the field.