**Linear surveying** involves measurement of distances between points on the surface of the **earth**. There are various **methods** of linear surveying and their relative merit depends upon the **degree of precision** (accuracy) required.

## Methods of Linear Surveying

Linear **surveying methods** can be broadly divided into three heads:

- Direct measurement
- Measurement by optical means
- Electronic methods

### Direct Measurement

In this surveying method, **distances** are actually measured on the surface of the earth by means of **chains**, **tapes**, etc.

### Measurement by Optical Means

In this method, observations are taken through a **telescope** and distances are determined by **calculation** as in tachometer or triangulation.

### Electronic Methods

In these linear surveying methods, distances are measured with instruments that rely on propagation, reflection and subsequent reception of either radio or light waves. The various instruments that are used under the electronic methods are

(i) **geodimeter**,

(ii) **tellurometer**,

(iii) **decca navigator**, and

(iv) **lambda position fixing system**.

The distance measured in the case of **geodimeter** is based on the propagation of modulated light waves. The other **three instruments** use radio waves for distance measurement.

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