Question

The correction in elevations due to the curvature and refraction is proportional to :

where R is the radius of curvature of Earth and D is the horizontal distance.

• A. D/R
• B. $R/D^2$
• C. $D^2/R$
• D. R/D

Answer 1

The correct option is C $D^2/R$

The effect of the curvature of earth and refraction is to be considered when the sights are long. in such case horizontal line is not a level line.


Correction due to the curvature

$C_c=-0.0785d^2$

Remember

where $C_c$ is in meters and d in kilometers.

Correction due to the curvature is negative.

In general, the correction due to refraction is $\frac{1}{7}of{C}_r$ and positive in magnitude.

$C_r=+0.0112d^2$

Remember