Test: Plane Table Surveying & Calculation of Area & Volume - 2 - Civil Engineering (CE) MCQ

Telescopic alidade

Explanation:
Plane table surveying is a graphical method of surveying in which the fieldwork and plotting are done simultaneously. It is used to map the details of the topography of the land. The main instrument used in plane table surveying is the alidade. There are different types of alidades, such as plain alidade and telescopic alidade.

1. Telescopic alidade: This is an alidade with a small telescope mounted on it. The telescope helps in sighting more accurately and can measure horizontal and vertical distances directly. It has a stadia diaphragm with horizontal stadia hairs, which allows for the direct measurement of distances by multiplying the staff intercept by the stadia multiplying constant. Thus, telescopic alidade is the correct answer.

2. Plain alidade: This is a simple, straight-edged ruler with a vertical sight vane at each end. It is used for sighting and drawing lines on the plane table sheet. However, it does not provide direct measurement of distances.

3. Tacheometer: This is a type of theodolite with a stadia diaphragm, specially designed for rapid measurements of horizontal and vertical distances. It is not used in plane table surveying.

4. Clinometer: This is an instrument used to measure the angles of slope or elevation of an object with respect to gravity. It is not used in plane table surveying for the direct measurement of horizontal and vertical distances.

Mid-ordinate and Average ordinate methods are used with the assumption that the boundaries between the extremities of the ordinates are straight lines.
Trapezoidal method is based on the assumption that the figures are trapezoids. The method is more accurate than the above two methods.
Simpson’s method assumes that the short lengths of the boundaries between the ordinates are parabolic arcs. This method is more useful when the boundary line departs considerably from the straight line. The results obtained by use of Simpson’s method in all cases are more accurate.