Measurement of horizontal angle with theodolite including example

Angle measurement

For angle measurement with theodolite vertical hair is used. Basically, there are two methods horizontal angle measurement,

• Repetition method (For single angle)

• Reiteration method (For more than one angle)

1. By Repetition method

Let suppose it is desire to measure the angle A from the following figure. We will use repetition method for this purpose.

Procedure

• Setup the theodolite at station A.

• Bisect the point B with vertical hair of theodolite and move telescope in clockwise and direction to bisect at point C.

• Note this circle reading in the book and fix this circle reading, then again bisect the point B by keeping the circle reading fixed.

• Now, release the circle reading and rotate the telescope again in clockwise direction till it bisect again point C.

• Similarly get 3rd and 4th repetition and note the circle reading after 4th repetition in the book.

• Change the face of telescope and repeat the above steps, an example and method of booking observations have given below,

 2. By Reiteration method

This method is used if there are more than one angles to be measure from a certain station point. Consider the following figure, we will measure angles AOB and BOC using this method.

Procedure

• Setup the theodolite at station O, bisect the point A with a certain circle reading with face left.

• Rotate the instrument in clockwise direction and bisect B, note the circle reading.

• Then rotate and the telescope till it bisect the point C, note this circle reading also. All these reading will book into face left position.

• Transit the telescope and rotate the instrument through 180°, this time bisect the point C firstly and then rotate telescope in anticlockwise direction towards B and then ultimately towards A. Put these readings in face right position.

• You can do more than one sets of measurements for the accurate results, I have done one set and booking method is as follows,

 One should start observation with some initial circle reading say 25°, if we start our observation with zero circle reading our calculations for computing mean will be little bit difficult.