Tacheometry 1

TACHEOMETRY
Tacheometry is the branch of Surveying in which we determine the horizontal and vertical
distances with the angular measurements with an instrument , Tachemometer. It is not so
accurate method of finding the horizontal distances as the Chaining is, but it is most suitable for
carrying out the surveys to find the distances in the hilly area where other methods are quite
difficult being carried out. It is generally used to locate contours, hydrographic surveys and
laying out routes of highways, railways etc.
Aim:
To determine the additive and multiplication constant of Tacheometer by Stadia Tacheometry.
Instruments Required:
Tacheometer with stand, Stadia Rod,Levelling Staff, Ranging rods, tape.
General:
An ordinary transit theodolite fitted with stadia hair is known as Tacheometer. This method
completely eliminated the use of tape or chain and is vary rapid and convenient.
Procedure:
1. Setup the instrument at A.
2. Measure a line AB, 120metres long on a fairly level ground and fix arrows at 30m intervals.
3. Note down the stadia hair readings (top, middle, bottom) by placing the staff over the arrow
stations (PQRS).
4. Keep the vertical circle to read zero during observations.
5. Calculate the other staff intercepts in the manner.
Calculation:
Stadia intercept:
S = Difference of top and bottom hair readings.
Let S1 is the staff intercept corresponding to distance D1 and S2 corresponding to D2.
By using tacheometric equation.

D= f/i S + ( f + d ), since vertical angle is zero.
Where, f/i = Multiplying constant denoted by K
and, ( f + d ) = additive constant denoted by C
then, D = KS + C
Now we have,
D1 = KS1 + C
D2 = KS2 + C
Solving the above two equations to get the values for K and C.
Similarly find out the values for K and C, by other set of readings.
The average values of the K and C will be the tacheometric Constants.
(a) Staff held vertical:
Tacheometry -Staff held vertical
D = (f/i).s+ (f+d)
where, f/i = multiplying constant
s = staff intercept between the bottom and top hair
f+d = Additive constant

D = Horizontal distance between the staff station and the observer's position
(b) Inclined sights staff held vertical:
D = (f/i).s. cos^2A + (f+d) cosA
V = {(f/i).s.} .[{sin(2A)}/2] + (f+d) sinA
Where A is the angle of elevation or angle of depression.
(c) Inclined sights upwards, staff held normal:
D = [(f/i).s+ (f+d)]cosA - h.sinA ; V= [(f/i).s+ (f+d)].sinA
h= central hair reading.
R.L. of staff = H.I. + [(f/i).s+ (f+d)].sinA - hcosA
(d) Inclined sights downwards, staff held normal:
D = [(f/i).s+ (f+d)]cosA - h.sinA ; V= [(f/i).s+ (f+d)].sinA
R.L. of staff = H.I. + [(f/i).s+ (f+d)].sinA – hcosA

Tacheometry 1

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