Theodolite introduction

THEODOLITE INTRODUCTION

    

 INTRODUCTION

 The theodolite is an intricate instrument used mainly for accurate measurement of horizontal and vertical angle up to 20". The following are the different purposes for which the theodolite can be used:

1. Measuring horizontal angles 

2. Measuring vertical angles

3. Measuring deflection angle

4. Measuring magnetic bearing 

5. Measuring horizontal distance between two points 

6. Finding the vertical height of an object

7. Finding the difference of elevation between various points

8. Ranging a line

  Theodolites may be of two types - 1. Transit theodolite, and 2. Non transit theodolite

  In the transit theodolite, the telescope can be revolved through a complete revolution about its horizontal axis in a vertical plane.

 In non transit theodolite, the telescope can not be revolved through a  complete revolution in vertical plane. But it can be revolved to a certain extent in the vertical plan, in order tomeasure the angle of elevation or depression.

PARTS OF A THEODOLITE

DEFINITIONS

1.Centring: 

  The setting of a theodolite exactly over a station mark by means of a plumb-bob is known as centring. The plumb-bob is suspended from a hook fixed below the vertical axis.

2.Transiting:

   The method of turning the telescope about its horizontal axis in a vertical plane through 180 degree

is termed as transiting. In other words, transiting results in a change in face.

3. Face left:

   If the vertical circle of the theodolite is on the left of the observer at the time of taking reading(The passion of theodolite is called face left condition/Telescope normal condition/bubble up condition).The observer taken in the face left position is called face left observation.

4. Face right:

  If the vertical circle of the theodolite is on the right of the observer at the time of taking reading(the passion of theodolite is called face right condition/Telescope inverted condition/bubble down condition).The observer taken in the face right position is called face right observation.

5. Line of collimation:

  It is an imaginary line passing through the intersection of the cross hairs at the diaphragm and the optical centre of the object glass and its continuation.