Understanding Distance Measurement Methods in Surveying

In surveying, measuring distances is a fundamental task. Distances can be measured using different techniques, which are broadly classified into two main categories: Direct Measurement and Indirect Measurement.

Direct Distance Measurement Method

Direct measurement involves physically laying a measuring instrument along the line to be measured. Examples of instruments used for direct measurement include:

• Measuring tapes (steel, cloth)
• Chains (Gunter's chain, Engineer's chain)
• Rods

This method is straightforward but can be time-consuming and may be affected by obstacles or uneven terrain.

Indirect Distance Measurement Method

Indirect measurement involves determining the distance without physically placing the measuring instrument directly along the entire line. Instead, it uses principles of trigonometry, optics, or electromagnetic wave propagation. The distance is calculated based on observations made with specialized instruments.

The question mentions instruments and techniques like:

• Instruments using radio or light waves (Electronic Distance Measurement or EDM instruments like Geodimeters, Total Stations). These instruments measure the time it takes for electromagnetic waves to travel from the instrument to a reflector and back, or measure phase differences to calculate the distance.
• Geodimeters: These are early types of EDM instruments that use light waves.
• Tacheometry: This is a surveying method used to quickly determine the horizontal and vertical distances to points using optical instruments like a theodolite or tacheometer, often based on measuring the stadia interval and vertical angle. This method relies on trigonometric principles.

These instruments and methods calculate the distance based on principles other than direct physical application of the measuring scale along the line. Therefore, they fall under the category of Indirect distance measurement.

Conclusion: Identifying the Correct Method

Based on the definitions, instruments like Geodimeters, Tacheometry, and those using radio or light waves for distance measurement employ techniques where the distance is not measured by directly applying a scale along the ground. They calculate the distance indirectly using electromagnetic principles or trigonometry.

Thus, the methods described in the question belong to the Indirect distance measurement method.