Explain principle of tachometry survey.
Principle of tachometry is based on principle of similar triangle in which corresponding sides & altitudes are proportional.
The ratio of distance of base from apex and length of base is always Constant.
In fig. O1a1a2 , O1b1b2 , O1c1c2 are all isosceles triangles where D1 ,
D2, D3 are the distances of bases from the apices and S1, S2, S3 are the
Lengths of the bases.
According to stated principle.
D1/ S1 = D2/ S2 = D3 / S3 = Constant
f/i= Multiplying constant.
f= Focal length of objective.
i= Stadia Intercept.