Correct Answer - Option 3 : Alidade
Alidade: It is an instrument used in plane table survey. It is a wooden or brass ruler of about 50-60 cm in length. It is also known as sight rule. Two vanes, the “object vane” and the “sight vane” are hinged at its two ends.
Four methods of Plane table surveying are:
1. Radiation
2. Intersection
3. Traversing
4. Resection
Radiation and intersection are the methods used for plotting the position of objects on the drawings.
Traversing and Resection are the methods used for locating the position of instrument station on the drawing.
Methods generally employed in Resection are:
a) By Compass
b) By Back orientation
c) By Three Point Problem
d) By Two Point Problem
Three Point Problem can be solved by:
i) Tracing Paper method
ii) Bessel's Graphical method
iii) Lehman's method
