THEODOLITE SURVEY
THEODOLITE : The theodolite is a complex instrument used mainly for accurate measurement of horizontal and vertical angle up to 10" or 20" depending upon the least count of the instrument.
Because of its various uses, the theodolite is sometimes known as "Universal Instrument".
USES OF THEODOLITE : Following are the different purpose for which theodolite can be used-
1) measuring horizontal angle
2) measuring vertical angle
3) measuring deflection angle
4) measuring magnetic bearing
5) measuring the horizontal distance between two points
6) finding vertical height of an object
7) finding difference of elevation between various points
8) ranging of a line
TYPES OF THEODOLITE :
Theodolites may be broadly classified into two types-
1) Transit theodolite
2) Non- transit theodolite
TRANSIT THEODOLITE - In the transit theodolite, the telescope can be revolved through a complete revolution about its horizontal axis in a vertical plane.
NON-TRANSIT THEODOLITE - In the non transit theodolite, the telescope cannot be revolved through a complete revolution in the vertical plane.
IMPORTANT TERMS RELATED TO THEODOLITE SURVEY :
CENTERING : The setting of theodolite exactly over a station marked by means of plumb bob is known as centering.
TRANSITING : The method of turning the telescope about its horizontal axis in a vertical plane through 180' is termed as transiting.
In other words, transiting results in a change of face.
FACE LEFT : It means that the vertical circle of theodolite is on the left of the observer at the time of taking reading.
FACE RIGHT : This refers to the situation when the vertical circle of the instrument is on the right of the observer when the reading is taken.
CHANGING FACE : The operation of bringing the vertical circle from one side of the observer to the other is known as changing face.
SWINGING THE TELESCOPE : This indicates turning the telescope in a horizontal plane. It is called 'right swing' when the telescope is turned clockwise and 'left swing' when the telescope is turned anticlockwise.
LINE OF COLLIMATION : It is an imaginary line passing through the optical center of the objective glass and its continuation.
AXIS OF TELESCOPE : The axis is an imaginary line passing through the optical center of the object glass and optical center of eyepiece.
AXIS OF THE BUBBLE TUBE : It is an imaginary line tangential to longitudinal curve of bubble tube at its middle point.
VERTICAL AXIS : It is the axis of rotation of the telescope in the horizontal plane.
HORIZONTAL AXIS : It is the axis of rotation of the telescope in the vertical plane.
TEMPORARY ADJUSTMENT : The setting of the theodolite over a station at the time of taking any observation is called temporary adjustment.
PERMANENT ADJUSTMENT : When the desired relationship between fundamental lines is disturbed , then some procedures are adopted to establish this relationship. This adjustment is known as permanent adjustment.
COMPONENTS OF TRANSIT THEODOLITE :
