Question

What are the tacheometric constants and write its valve?

Answer 1

The stadia interval factor (K) and the stadia constant (C) are known as tacheometric constants. Before using a tacheometer for surveying work, it is reqired to determine these constants. These can be computed from field observation by adopting following procedure.

• Step 1 : Set up the tacheometer at any station say P on a flat ground.

• Step 2 : Select another point say Q about 200 m away. Measure the distance between P and Q accurately with a precise tape. Then, drive pegs at a uniform interval, say 50 m, along PQ. Mark the peg points as 1, 2, 3 and last peg -4 at station Q.

• Step 3 : Keep the staff on the peg-1, and obtain the staff intercept say s1 .

• Step 4 : Likewise, obtain the staff intercepts say s2, when the staff is kept at the peg-2,

• Step 5 : Form the simultaneous equations, using Equation (23-2)

D1 = K. s 1 + C --------------(i)

and D 2 = K. s 2+ C -------------(ii)

Solving Equations (i) and (ii), determine the values of K and C say K1 and C1 .

• Step 6 : Form another set of observations to the pegs 3 & 4, Simultaneous equations can be obtained from the staff intercepts s3 and s4 at the peg-3 and point Q respectively. Solving those equations, determine the values of K and C again say K2 and C2.

• Step 7 : The average of the values obtained in steps (5) and (6), provide the tacheometric constants K and C of the instrument.