# Tacheometric Surveying

Tacheometric surveying is a reliable and efficient method of measuring land, buildings, and other physical features in order to create detailed maps, plans, and digital models. Using specialized equipment and advanced techniques, tacheometric surveying allows for highly accurate and precise measurements, making it an invaluable tool in various industries such as construction, engineering, and urban planning. In this article, we will delve into the history of tacheometric surveying, its principles, and its practical applications, shedding light on the importance of this surveying technique in modern-day mapping and development.

## Principle of Tacheometric Surveying

The principle of tacheometric surveying is based on the use of specialized equipment and methods to accurately measure and record data on a construction site. This type of surveying is commonly used in civil engineering projects to gather precise information about the topography and features of the land.

The first principle of tacheometric surveying is the use of a tacheometer, which is a modernized version of a theodolite. This is a highly accurate instrument that measures the vertical and horizontal angles of a point in space, as well as the horizontal and vertical distances. The tacheometer also includes an internal telescope, which allows the surveyor to focus on specific points and take readings.

Another key principle of tacheometric surveying is the stadia method. This involves using stadia hairs, which are placed in the eyepiece of the tacheometer. These hairs have particular spacings that allow the surveyor to estimate the distance to the target point based on the height difference between them. By reading the horizontal and vertical angles at the same time, the tacheometer can calculate the distance to the target with a high degree of accuracy.

The third principle of tacheometric surveying is the use of stadia rods. These are staffs or poles that are set up at various points on the construction site. The rods are usually marked with special scales that correspond with the stadia hairs in the tacheometer. Surveyors can then take readings and record the distances and heights of the points they are surveying.

Another important principle of tacheometric surveying is the proper setup and leveling of the tacheometer. The instrument must be carefully aligned and leveled before each reading to ensure accurate results. Any errors in this setup can lead to incorrect data and inaccurate measurements.

To achieve the highest level of accuracy, the surveyor must also take into consideration the curvature of the Earth and other factors that may affect the measurements, such as refraction and atmospheric conditions. These factors can be compensated for by using specialized correction factors and formulas.

In conclusion, the principle of tacheometric surveying relies on the use of specialized equipment and precise methods to gather accurate data on a construction site. With proper setup and careful consideration of various factors, this type of surveying can provide valuable information for civil engineers to plan and execute projects with a high level of precision.

## Methods of Tacheometric Surveying

Tacheometric surveying, also known as stadia surveying, is a widely used method of surveying in civil engineering. This technique is based on the principle of using an instrument known as the tacheometer, which enables the surveyor to measure both horizontal and vertical distances simultaneously. The following methods are commonly used in tacheometric surveying:

1. Stadia method: This is the most commonly used tacheometric method. In this method, two horizontal lines, called stadia hairs, are placed in the telescope of the tacheometer. The surveyor then measures the distance between the two hairs on the vertical rod held by the staffman, known as the stadia rod. This method is based on the stadia constant, a known value that is used to calculate the distance.

2. Tangential method: This method is based on the principle of tangents. The surveyor looks through the telescope of the tacheometer in such a way that the line of sight is tangent to the staff held by the staffman. The stadia hairs are used to measure the distance between the horizontal crosshair and the point where the tangent intersects the vertical rod. This method is more accurate than the stadia method but requires more mathematical calculations.

3. Subtense method: In this method, the surveyor measures the angle subtended by the staff at the instrument station. The subtended angle is then used to calculate the distance between the instrument and the staff. This method is more accurate and faster than the tangential method but requires the use of specialized instruments.

4. Vertical angle method: As the name suggests, this method is based on the vertical angle between the tacheometer and the staff. The surveyor measures the vertical angle by rotating the telescope of the instrument from horizontal to the desired angle. This method is used when the terrain is steep or when the distance is too long for the stadia method.

5. Horizontal angle method: This method is used to measure the distance between two points that are not in a straight line. The surveyor measures the horizontal angle between the two points using the telescope of the tacheometer. This angle is then used to calculate the distance between the points using mathematical calculations.

In conclusion, tacheometric surveying offers a fast and accurate way of measuring distances in civil engineering projects. The choice of method depends on the terrain, length of the distance, and required accuracy. With the advancement of technology, tacheometers are now equipped with electronic distance measuring devices, making this method even more efficient and precise.

## Tangential Method of Tacheometric Surveying

Tangential method of Tacheometric Surveying is a popular technique used by civil engineers to measure horizontal distance, vertical angle, and difference in elevation in a surveying project. This method utilizes a tacheometer, a type of total station instrument, which combines the features of a theodolite and stadia diaphragm to provide accurate measurements.

The procedure of tangential method starts with setting up the tacheometer at the desired location, which is usually on a tripod. The instrument is then leveled and the vertical circle is set to zero. This helps in measuring the vertical angles with respect to the horizontal plane.

Next, the target rod is held vertically on the point to be measured and the crosshairs of the telescope are focused on the base of the rod. The target rod has graduations on its surface, which are read with the help of a stadia diaphragm inside the tacheometer. This diaphragm has two horizontal crosshairs, known as stadia hairs, which are placed symmetrically with respect to the vertical crosshair. The stadia hairs intercept the rod graduations and provide accurate readings.

The angular readings are then recorded and the instrument is moved to the next station where the same procedure is repeated. By recording multiple readings from different stations, a series of triangles are formed that enable the calculation of the horizontal and vertical distances. This method is called tangential because the triangles formed are tangent to the curved surface of the earth.

The accuracy of the tangential method is dependent on the accurate measurement of the vertical angle and the stadia readings. The stadia constant, which is the distance between the stadia hairs, needs to be determined beforehand to ensure precise measurements. With advancements in technology, modern tacheometers now come equipped with auto-stadia, which eliminates the need for manual reading and improves the accuracy of measurements.

One of the major advantages of the tangential method of Tacheometric Surveying is its speed and efficiency. With the use of a single instrument, the tacheometer, all the required measurements can be obtained quickly, thus saving time and effort. Additionally, this method is suitable for all types of terrain, including rugged and hilly terrains.

In conclusion, the tangential method of Tacheometric Surveying is a valuable tool for civil engineers as it provides accurate measurements in a shorter period of time. Its versatility and efficiency make it a preferred choice for surveys in various industries, including construction, mining, and infrastructure development.

## Procedure of Tacheometric Surveying

Tacheometric surveying, also known as stadia surveying, is a method used in civil engineering to measure horizontal and vertical distances using an optical instrument called a tacheometer. This technique is often used for topographic mapping, site planning, and construction projects. The procedure for conducting a tacheometric survey is outlined below:

Step 1: Determine the Purpose of the Survey

Before beginning a tacheometric survey, the purpose and scope of the survey must be determined. This will help in selecting the appropriate equipment, techniques, and accuracy requirements for the project.

Step 2: Set Up the Tacheometer

The tacheometer should be set up on a stable and level tripod at a known reference point. The instrument should be properly adjusted and calibrated before starting the survey.

Step 3: Establish the Baseline

A baseline is a straight line on the ground along which the survey measurements will be taken. It should be established using traditional surveying techniques such as chaining or theodolite traversing.

Step 4: Take a Backsight Reading

The backsight reading is the first measurement taken with the tacheometer. It is taken from the known reference point and is used to determine the horizontal and vertical angles of the other points on the baseline.

Step 5: Take Intermediate Readings

Intermediate readings are taken along the baseline at predetermined intervals. These readings are made by aligning the stadia hairs on the tacheometer with the target positioned at the desired point and measuring the horizontal and vertical angles.

Step 6: Take a Foresight Reading

The foresight reading is taken from the last intermediate point to the tacheometer. It is used to check the accuracy of the survey and to close the survey loop.

Step 7: Repeat the Process for Additional Baselines

If the surveyed area is large, multiple baselines may need to be established and surveyed using the above procedure. The starting point for a new baseline should be the endpoint of the previous baseline.

Step 8: Calculate the Coordinates

Once all the measurements have been taken, the horizontal and vertical distances between the points can be calculated using trigonometry. These coordinates can then be plotted on a map or transferred to a digital software for further analysis.

Step 9: Check for Errors and Adjust

A check should be performed to ensure that the survey results are accurate. If any errors are found, adjustments can be made using mathematical methods such as proportional parts or least squares adjustment.

Step 10: Present the Survey Results

The final step in a tacheometric survey is to present the results in a clear and easy-to-understand format. This can be done through maps, plans, or digital presentations.

In conclusion, tacheometric surveying is a simple, efficient, and accurate method for measuring distances in civil engineering projects. By following the above procedure, engineers can obtain precise and reliable data for their design and construction work.

## Conclusion

In conclusion, tacheometric surveying is a highly efficient and accurate method of collecting data for topographical surveys. Its use of specialized equipment and mathematical calculations allows for quick and precise measurements, making it a valuable tool for various engineering and construction projects. By understanding the principles and techniques of tacheometry, surveyors can produce comprehensive and detailed maps, plans, and cross-sections to aid in the planning and execution of various infrastructure projects. As technology continues to advance, tacheometric surveying techniques and equipment will also continue to evolve and improve, further increasing its importance in the field of surveying.