Tacheometry

Tacheometry is a branch of survey in which height and distance are determined  from the instrumental reading alone ,these reading are usually taken with a  specially adopted theodolite khown as tachometer.
 Chaining operation is eliminited and tacheometry is very useful in broken terrain .eg . river valley over standing crops e.t.c.

Propose of tacheometric surveying :

1) preparation of typographical map,vertical and horizontal control can be done at same time.

2) In survey of higher accuracy ,it provides check on the distance measured by  tape 

3) For surveys up to the error 1/1000 is accepted

4)It is considered to be rapid and widely used by engineers in location survey for railways, canals reservoirs etc.

Field works on tacheometry

The tacheometric survey involves two steps:

1.Running a traverse enclosing the area.

2.Locating details and contours from the traverse station .

Procedure

1) Measure the bearing of first line.

2)set up the instrument over the first station ,centering and level it accurately.

3)Measure heigh of instrument 

4)Determine the Rl of first station by observing the staff on the BM or TBM

5)Locate the detail points around the station by:

    a)horizontal angle between the reference          station and the point

    b)vertical angle 

    c)staff reading of the stadia hairs

6) Take the foresight on the second station by observing 

  a)Traverse angle

 b) vertical angle 

c) staff reading

7) transfer the instrument to the second stations

8) Center and level it accurately and measure height of the instrument (HI).

9) Sight the first station and observed 

a)Traverse angle

b) The vertical angle

c)staff reading

10)compute the traverse leg between two stations and their diffence in elevation from the observation made from both station .If required accuracy is achieved then the average should be accepted .if not,repeat the observation at both station

11) locate the detail points.

12) shift the instrument to another station and repeat the same procedures.