Telescopic Alidade in Plane Tabling

In plane tabling, a telescopic alidade is the instrument used to obtain both horizontal and vertical distances directly without the need for chaining. It is a crucial tool in the field of surveying and is widely used for topographic mapping and contouring.

What is Plane Tabling?

Plane tabling is a method of surveying that involves the graphical representation of the ground features on a plane table. The process involves setting up a plane table at a specific location and then observing and recording the details of the surrounding area. These details are later used to create a map. Plane tabling is particularly useful in situations where rapid and accurate mapping is required.

Functions of a Telescopic Alidade

A telescopic alidade is an integral part of the plane table setup. It serves multiple functions that aid in the accurate measurement and mapping of the terrain. The main functions of a telescopic alidade include:

1. Measuring Horizontal Distances: The telescopic alidade is equipped with a telescopic sight that enables the surveyor to precisely sight and measure horizontal distances. This is achieved by aligning the sight with a specific point on the terrain and then reading the corresponding distance on the alidade's scale.

2. Measuring Vertical Angles: The alidade is also equipped with a vertical scale or vernier that allows the surveyor to measure vertical angles. These angles are crucial for determining differences in elevation and creating contour lines.

3. Measuring Vertical Distances: By combining the measured vertical angles with the known horizontal distances, the telescopic alidade enables the surveyor to calculate vertical distances or differences in elevation. This information is essential for contouring and topographic mapping.

4. Recording Observations: The telescopic alidade often includes a leveling bubble and a spirit level. These tools help in ensuring the accuracy of the measurements by allowing the surveyor to level the instrument properly.

Advantages of a Telescopic Alidade

The use of a telescopic alidade in plane tabling offers several advantages:

- It provides a direct and efficient method of measuring both horizontal and vertical distances without the need for time-consuming and error-prone chaining.

- The telescopic sight allows for precise targeting and measurement of specific points on the terrain.

- The vertical scale and vernier enable the surveyor to accurately measure vertical angles and calculate vertical distances.

- The leveling bubble and spirit level ensure the instrument is properly leveled, minimizing errors in the measurements.

- The telescopic alidade is portable and easy to set up, making it suitable for fieldwork and rapid mapping.

In conclusion, a telescopic alidade is an essential instrument in plane tabling as it allows for the direct measurement of horizontal and vertical distances without the need for chaining. It offers accuracy, efficiency, and ease of use, making it a valuable tool for surveying and mapping purposes.

Telescopic Alidade: Obtaining Horizontal and Vertical Distances in Plane Tabling

Introduction:
In the field of surveying, plane tabling is a method commonly used to obtain accurate measurements and create detailed maps. One of the essential instruments used in plane tabling is the telescopic alidade. It enables surveyors to obtain both horizontal and vertical distances directly without the need for chaining.

Definition of Telescopic Alidade:
The telescopic alidade is a surveying instrument that consists of a telescopic sight mounted on a tripod. It is designed to measure both horizontal and vertical angles. The word "alidade" originates from the Arabic term "al-idad," which means "the instrument for sighting."

Function of Telescopic Alidade in Plane Tabling:
The telescopic alidade serves several functions in plane tabling, including:

1. Measuring Horizontal Distances:
The telescopic alidade is equipped with a sighting telescope, which allows surveyors to visually align the instrument with specific points or features on the ground. By rotating the alidade and aligning the telescope with different points, surveyors can measure the horizontal angles between these points.

2. Measuring Vertical Distances:
The telescopic alidade is also equipped with a vertical arc or clinometer, which enables surveyors to measure vertical angles. By sighting through the telescope and reading the angle on the vertical arc, surveyors can determine the difference in elevation between two points.

3. Direct Measurement without Chaining:
Unlike traditional surveying methods that require the use of chains or tapes to measure distances, the telescopic alidade allows surveyors to obtain horizontal and vertical distances directly. This eliminates the need for time-consuming and potentially error-prone chaining procedures.

4. Achieving Accurate Results:
The telescopic alidade provides surveyors with a precise and reliable means of measuring both horizontal and vertical distances. The use of a telescopic sight allows for accurate pointing and alignment, resulting in more accurate measurements and map creation.

In Conclusion:
The telescopic alidade is an indispensable instrument in plane tabling, allowing surveyors to obtain horizontal and vertical distances directly without resorting to chaining. Its telescopic sight and vertical arc enable precise measurement of angles, leading to accurate and reliable results. By utilizing the telescopic alidade, surveyors can efficiently carry out surveys, create detailed maps, and contribute to various civil engineering projects.