Theodolite Surveying

Theodolite surveying is a method of surveying that accurately measures horizontal and vertical angles.

A theodolite is a highly precise device used to evaluate horizontal and vertical distances between two points.

It is also known as a “universal instrument” because of its wide range of applications.

In this article you’ll learn:

• What is theodolite surveying?
• Types of reconnaissance survey.
• Merits and Demerits of reconnaissance survey.
• Lots more.

So, if you’re ready to go with theodolite surveying, this article is for you.

Let’s dive right in.

Introduction to Theodolite Surveying:

Theodolite is a universal device that can be used for a variety of tasks in surveying.

For determining horizontal angles, vertical angles, and deflection angles. For determining the size of magnetic bearings.

To determine the distance between two points on the horizontal plane and the object’s vertical height.

Parts of Theodolite and their Functions:

Telescope:

A typical theodolite consists of a movable telescope set within two perpendicular axes—horizontal and vertical.

A telescope is a focusing apparatus that has an object section on one end and an eye section on the other.

 In the vertical plane, it revolves around the horizontal axis. The graduations are precise up to 20′.

Vertical Circle:

The vertical circle is connected to the telescope and moves in parallel with it. Each quadrant has a numbered graduation from 0 to 90 degrees.

Index Frame:

It’s also known as a vernier frame or a t-frame. It has two vertical and horizontal arms.

 The vertical arm is used to secure the telescope at the desired level, while the horizontal arm is used to measure vertical angles.

Standards:

The frames that support the telescope and allow it to spin around its vertical axis are known as standards.

These are usually in the shape of an A. As a result, standards are often known as A-frames in theodolite surveying.

Upper Plate:

It’s also known as a vernier plate.

 The standards are supported by the top surface of the upper plate.

It also has an upward clamping screw in relation to the tangents screw, which supports the attachment to the lower plate.

When the upper clamping screw is set, the upper and lower plates are joined and moved along with some relative motion according to the upper tangent screw.

Two verniers with magnifiers are also set diagonally on the upper plate and two inner spindles are attached to it.

Lower Plate:

Scale plate is another term for this. It has a graduated scale with readings ranging between 0 to 360.

It consists of a lower clamping screw that is connected to the outer spindle.

If the bottom clamp screw is loose as well as the upper clamp screw is tight, both plates might spin jointly.

 Only the upper plate is accessible when the lower clamping screw is tightened while an upper clamp is removed, whereas the lower plate is attached by the control plans plate in theodolite surveying.

Levelling Head:

The levelling head has two tribrach plates, which are similar to triangular plates.

The levelling screws on the three extremities of the upper tribrach plate are used to level the upper plate and telescope.

The lower tribrach plate is the part of the tripod stand that connects to the lower tribrach plate.

Shifting Head:

Two parallel plates are moved one over the other in a short region by the shifting head.

Below the lower plate is a spinning head. It’s a good idea to focus the entire instrument on the station.

Plate Level:

The plate levels, which are in a direction perpendicular to each other and one of which is parallel to the application to the different axis, are carried on the top plate.

These plate levels contribute to the accurate vertical alignment of the telescope in theodolite surveying.

Tripod:

Theodolite is fixed on a tripod, which is nothing more than a support. It should be in such a position that the theodolite is completely levelled.

The tripod has steel shoes at the ends of its legs. When installed, these have a tight grip on the earth and do not move.

An external screw on the tripod aids in the attachment of the theodolite to the tribrach plate in a fixed position.

Plumb Bob:

A plumb bob is a tool with a long thread and a cone-shaped weight. The weight is suspended from the tripod stand’s center via a thread.

Magnetic Compass:

In the centre of the upper plate of simpler theodolites, there is a circular compass box. It will be beneficial if we choose north as the reference point.

Types of Theodolite Surveying:

1. Transit Theodolite:

A transit Theodolite has a telescope that may be adjusted in a vertical plane by rotating the equipment completely around its horizontal axis.

2. Non-Transit Theodolite:

This is in complete conflict with Transit Theodolite.

With this sort of Theodolite, the telescope cannot be turned completely around its horizontal axis in a vertical plane.

 To a point, it can be turned to produce vertical angles.

On the basis of the scale employed in theodolites, theodolites can be divided into two categories:

3. Vernier Theodolite:

 A Vernier Scale is included with the Vernier Theodolite.

In typical surveying activity, Vernier Theodolites are most usually utilized.

4. Micrometer Theodolite:

 A micro micrometer scale is included.

The diameter of a theodolite’s main scale is used to measure its size; for example, a 10 cm theodolite has a diameter of 10cm.

8 cm to 12 cm theodolites is frequently employed in surveying.

Advantages of Theodolite Surveying:

1. It’s a low-cost instrument.
2. They are extremely portable and can be brought practically into place with little effort.
3. Generally easier to use than public transportation or a level and compass.
4. As a result, it’s ideal for small-scale surveying tasks such as fields and construction sites.
5. Its basic components are simple to comprehend and use by anyone who is aware of the fundamentals of surveying tools.

Also read: Total Station

Disadvantages Of Theodolite Surveying:

1. It includes a bubble level, which makes it a little tough to use.
2. It provides a rough estimate.
3. When the object to be measured is too small or too far away.
4. The sight point is fixed in one location, it cannot be performed.
5. For precise measurements, it must be kept parallel to a horizontal level line, which indicates it must be levelled before taking an angle off of it.
6. It can’t be used to determine vertical angles in various stations at the same time.
7. Other surveying devices such as the transit and the theodolite are more accurate.

Also read: Plane Table Surveying

Application of Theodolite Surveying:

• Navigating.
• Meteorology.
• Putting the building’s edges and lines in place.
• Angles and straight lines are measured and drawn together.
• Walls with wood frames linked.
• Designing panels.
• Plumbing a column or a corner of a structure.

Also read: Compass Surveying

Conclusion:

We have learned the use of theodolite to measure horizontal and vertical angles as well as operate the instrument in the fields.

A typical theodolite consists of a movable telescope set within two perpendicular axes—horizontal and vertical.

We also know theodolite surveying includes Vernier, Optic, and Electronics theodolite.