EDM and Trigonometric Levelling

I. Introduction

In the field of surveying, Electronic Distance Measurement (EDM) and Trigonometric Levelling are two important techniques used to measure distances and elevations accurately. These techniques play a crucial role in various surveying applications, including construction projects, land surveying, mapping, and GIS.

II. EDM (Electronic Distance Measurement)

Electronic Distance Measurement (EDM) is a modern surveying technique that uses electronic instruments to measure distances accurately. It has replaced traditional methods such as taping and chain surveying due to its efficiency and precision.

A. Definition and Purpose of EDM

EDM is a method of measuring distances between two points using electromagnetic waves. It provides accurate and reliable measurements, making it suitable for various surveying applications.

B. Components and Working Principle of EDM

EDM instruments consist of several components that work together to measure distances. The main components include:

1. EDM Instrument: The instrument emits electromagnetic waves and measures the time it takes for the waves to travel to the target and return.
2. Reflective Prism: The prism reflects the electromagnetic waves back to the instrument.
3. Control Unit: The control unit processes the data received from the instrument and calculates the distance.

The working principle of EDM involves emitting electromagnetic waves towards a reflective prism placed at the target point. The instrument measures the time it takes for the waves to travel to the prism and back. By knowing the speed of the waves, the instrument calculates the distance between the instrument and the prism.

C. Types of EDM

There are three main types of EDM:

1. Taping EDM: This type of EDM uses a tape measure to measure distances. It is the most basic form of EDM and is suitable for short distances.
2. Pulsed EDM: Pulsed EDM instruments emit short pulses of electromagnetic waves and measure the time it takes for the pulses to travel to the target and return. This type of EDM is more accurate than taping EDM.
3. Continuous Wave EDM: Continuous Wave EDM instruments emit a continuous wave of electromagnetic waves and measure the phase difference between the emitted and received waves. This type of EDM provides high accuracy and is commonly used in advanced surveying applications.

D. Advantages and Disadvantages of EDM

Advantages of EDM:

• High accuracy and precision
• Fast and efficient measurements
• Suitable for various surveying applications

Disadvantages of EDM:

• Expensive equipment
• Requires skilled operators
• Limited range compared to other surveying techniques

E. Real-World Applications of EDM

EDM is widely used in various surveying applications, including:

1. Construction Projects: EDM is used to measure distances accurately for construction layout and setting out.
2. Land Surveying: EDM is used to establish property boundaries and measure land areas.
3. Mapping and GIS: EDM is used to collect data for creating accurate maps and geographic information systems.

III. Trigonometric Levelling

Trigonometric Levelling is a surveying technique used to determine height differences between points by measuring angles and distances. It is based on trigonometric principles and is commonly used in situations where direct levelling is not feasible.

A. Definition and Purpose of Trigonometric Levelling

Trigonometric Levelling is a method of determining height differences between points using trigonometric calculations. It is used when direct levelling is not possible due to obstacles or long distances.

B. Principles and Concepts of Trigonometric Levelling

Trigonometric Levelling is based on the following principles and concepts:

1. Angle of Elevation and Depression: The angle of elevation is the angle between the horizontal line of sight and an upward line of sight to a point. The angle of depression is the angle between the horizontal line of sight and a downward line of sight to a point.
2. Horizontal and Vertical Distances: Trigonometric Levelling involves measuring horizontal and vertical distances between points.
3. Trigonometric Functions: Trigonometric functions such as sine, cosine, and tangent are used to calculate height differences.

C. Step-by-Step Walkthrough of Trigonometric Levelling Process

The Trigonometric Levelling process involves the following steps:

1. Setting up the Instrument: The surveying instrument, such as a theodolite or total station, is set up at a known point with a known elevation.
2. Measuring the Angle of Elevation or Depression: The instrument is aimed at the target point, and the angle of elevation or depression is measured.
3. Calculating the Horizontal and Vertical Distances: Using trigonometric calculations, the horizontal and vertical distances between the instrument and the target point are determined.
4. Determining the Difference in Elevation: The difference in elevation between the instrument and the target point is calculated using trigonometric functions.

D. Advantages and Disadvantages of Trigonometric Levelling

Advantages of Trigonometric Levelling:

• Suitable for long distances and areas with obstacles
• Does not require a direct line of sight
• Can be performed with a theodolite or total station

Disadvantages of Trigonometric Levelling:

• Requires trigonometric calculations
• Less accurate than direct levelling
• Limited to height differences

E. Real-World Applications of Trigonometric Levelling

Trigonometric Levelling is used in various surveying applications, including:

1. Determining Height Differences in Surveying: Trigonometric Levelling is used to determine height differences between points in topographic surveys.
2. Monitoring Ground Movements in Engineering Projects: Trigonometric Levelling is used to monitor ground movements in construction and engineering projects.
3. Establishing Benchmarks for Construction Projects: Trigonometric Levelling is used to establish reference points for construction projects.

IV. Comparison between EDM and Trigonometric Levelling

A. Differences in Measurement Techniques

EDM and Trigonometric Levelling use different measurement techniques. EDM measures distances directly using electromagnetic waves, while Trigonometric Levelling calculates height differences using angles and distances.

B. Accuracy and Precision Considerations

EDM provides higher accuracy and precision compared to Trigonometric Levelling. However, Trigonometric Levelling can be used in situations where direct measurements are not possible.

C. Suitability for Different Surveying Scenarios

EDM is suitable for measuring distances accurately in various surveying applications. Trigonometric Levelling is suitable for determining height differences in situations where direct levelling is not feasible.

V. Conclusion

In conclusion, EDM and Trigonometric Levelling are two important techniques in surveying. EDM provides accurate distance measurements using electromagnetic waves, while Trigonometric Levelling calculates height differences using trigonometric principles. Both techniques have their advantages and disadvantages and are suitable for different surveying scenarios. Understanding the fundamentals and applications of EDM and Trigonometric Levelling is essential for surveyors to perform accurate and efficient surveying work.

Summary

EDM (Electronic Distance Measurement) and Trigonometric Levelling are two important techniques used in surveying. EDM uses electronic instruments to measure distances accurately, while Trigonometric Levelling determines height differences using trigonometric calculations. Both techniques have their advantages and disadvantages and are suitable for different surveying scenarios.

Analogy

Imagine you are a builder constructing a house. You need to measure the distances accurately for the layout and setting out of the construction. EDM is like using a laser tape measure that provides precise measurements quickly. On the other hand, Trigonometric Levelling is like using a theodolite or total station to determine the height differences between different points on the construction site. Both techniques are essential for ensuring the accuracy and efficiency of the construction process.