Stadia Constant determination

The stadia constant can be determined by:

• Laboratory measurement method
• Field measurement method
• Semi field method

In this method,

• The stadia intercept (i) can be measured from the diaphragm by means of using vernier caliper.
• The distance `c` between the optical center and the vertical axis of the tacheometer can also be measured.
• The focal length can be determined using lens formula as:

`1/f=1/u+1/v`

Thus, after measuring `f`,`i` and `c`, the constants `K` and `C` can be calculated as:

`K=f/i` and `C=f+c`

In this method,

A fairly leveled ground is selected and the tacheometer is set up at point `A` and another point, say `A_4` is also selected at a known distance, say 200m.The pegs are then driven at a regular intervals,say `50m` and let the points be `A_1`,`A_2`, and `A_3`.Now, holding the staff at `A_1`,`A_2`, ....

The stadia constant can be determined by:

• Laboratory measurement method
• Field measurement method
• Semi field method

Laboratory measurement method:

In this method,

• The stadia intercept (i) can be measured from the diaphragm by means of using vernier caliper.
• The distance `c` between the optical center and the vertical axis of the tacheometer can also be measured.
• The focal length can be determined using lens formula as:

`1/f=1/u+1/v`

Thus, after measuring `f`,`i` and `c`, the constants `K` and `C` can be calculated as:

`K=f/i` and `C=f+c`

Field measurement method:

In this method,

A fairly leveled ground is selected and the tacheometer is set up at point `A` and another point, say `A_4` is also selected at a known distance, say 200m.The pegs are then driven at a regular intervals,say `50m` and let the points be `A_1`,`A_2`, and `A_3`.Now, holding the staff at `A_1`,`A_2`, and `A_3`, the staff intercept `S_1`,`S_2`,`S_3`, and `S_4` are taken.

Let,

`A A_1=D_1`

`A A_2=D_2`

`A  A_3=D_3`

`A A_4=D_4`

Now, we know that,

`D_1=K*S_1+C`.....(i)

`D_2=K*S_2+C`.....(ii)

Thus, `D_2-D_1=K*S_2-K*S_1`

Or,`K=(D_2-D_1)/(S_2-S_1)`....(iii)

Where, `D_1`,`D_2`, `S_1`, `S_2` are known and hence `K` can be determined.

Now, from (i), we get,

`C=D_1-K*S_1`

Or, `C=D_1-(D_2-D_1)/(S_2-S_1)*S_1`

Or, `C=((D_1*S_2)-(D_2S_1))/(S_2-S_1)`

Similarly,

`k=(D_4-D_3)/(S_4-S_3)` and

`C=(D_3*S_4-D_4-S_3)/(S_4-S_3)`.....(iv)

Thus, the mean value of `K` and ` C` can be determined from the above equation.

Semi-Field Method:

In this method, the value of `K` is measured from field measurement method and the value of `C=f+c` is measured by means of measuring `f` and `c` in lab.