Question

An instrument was setup at P and angle of elevation to a vane 4 m above the foot of staff held at Q was $9^{\circ }{30}^{\prime }$. The horizontal distance between P and Q was known to be 2000 m. What is the R.L. (in m) of staff station Q?
[Given that the R.L of instrument axis was 2650.38 m and consider refraction and curvature corrections]

• A. 2571.10
• B. 2981.34
• C. 2773.83
• D. 3053.33

Answer 1

The correct option is B 2981.34

Height of vane above the instrument axis
$=Dtan\alpha =2000tan{9}^{\circ }{30}^{\prime }$

$=334.69m$

Correction for curvature and refraction $=\frac{6}{7}\frac{D^2}{2R}=0.06728D^{2}m\left(Disinkm\right)$

$=0.06728(2{)}^2=0.2691m\simeq 0.27m(+ve)$

Height of vane above instrument axis
$=334.69+0.27=334.96m$

$\therefore$ R. L of vane $=334.96+2650.38=2985.34m$

$\therefore$ R.L of Q $=2985.34-4=2981.34m$