Civil war Day 14 PWD-levelling,theodolite,Tacheometry& contourin

In trigonometric levelling, the measurement of elevation relies on which two key factors?

• Vertical angles and horizontal distance
• Horizontal angles and vertical distance
• Apparent vertical and horizontal distance
• Apparent vertical and horizontal angles

Answer explanation

Elevation is computed from the measured vertical angle and the horizontal distance between instrument and target.

What are the main components of a levelling head?

• Upper plate, foot screws, and lower plate
• Base, shaft, and upper plate
• Foot screws, lower plate, and gauge
• Upper plate, screws, and level

Answer explanation

A levelling head consists of upper and lower plates connected with three foot screws for precise instrument adjustment.

A level is set up at O on a line AB 60 m from A and 700 m from B. The back sight on A is 2.654 m and the fore sight on B is 2.786 m. Find the true difference of level between A and B.

• 0.072
• 0.063
• 0.099
• 0.0212

Answer explanation

True difference of level = 2.786 − 2.654 = 0.132 m; correction for curvature/refraction makes it approximately 0.099 m.

Contour interval is inversely proportional to

• Scale of map
• Purpose and extent of survey
• Nature of ground
• Both a and b

Answer explanation

The contour interval (C.I.) is the vertical distance between consecutive contour lines on a map.

It depends on several factors, but it is inversely proportional to:

1. Scale of the map —
   Larger scale → smaller contour interval (more detail).
   Smaller scale → larger contour interval.

2. Purpose and extent of survey —
   Detailed engineering works (like roads, buildings) need smaller contour intervals,
   while large-area topographical surveys use larger contour intervals

The process of spacing the contours proportionally, between the plotted ground points, is known as

• Profile levelling
• Orientation
• Cross-sectioning
• Interpolation

Answer explanation

Interpolation is used to estimate and plot contour lines proportionally between known elevations.

Which of the following methods of contouring is most suitable for a hilly terrain?

• Direct method
• Square method
• Cross sections method
• Tacheometric method

Answer explanation

In hilly terrain, tacheometric contouring is best since it quickly gives elevations and distances from angular measurements.

How many stadia hairs are provided in the diaphragm of the tacheometer?

• Two stadia hairs
• Three stadia hairs
• Four stadia hairs
• Five stadia hairs

Answer explanation

In a tacheometer, the diaphragm has three horizontal hairs in total — one central and two stadia hairs.

However, for tacheometric calculations, only the two stadia hairs (upper and lower) are used to determine distances.

Hence, a tacheometer has two stadia hairs used for measurement.

Which is used to measure the distance between the optical centre and the vertical axis of the instrument?

• Bevel protractor
• Vernier caliper
• Vernier micrometer
• Dial test indicator

Answer explanation

A Vernier caliper accurately measures small linear distances, such as between the optical center and instrument axis.

What is the name of theodolite with one of its telescope that cannot be revolved through 180° in a vertical plane about its horizontal axis?

• Auto level
• Dumpy level
• Transit theodolite
• Non-transit theodolite

Answer explanation

In a non-transit theodolite, the telescope cannot be rotated 180° vertically; transit types can.

What does the process of "lining in" involve in theodolite surveying?

• Establishing intermediate points on a straight line where both ends are intervisible
• Establishing intermediate points where both ends are not intervisible
• Establishing the center of the survey station
• Moving the instrument in a circular direction

Answer explanation

Lining in is done to locate intermediate points on a straight line between two intervisible stations.