Surveying (Part-3) (General Engineering) (SSC JE)

• A contour line joins all the points having equal elevation.
• A line on a map joining places of equal elevation is called a contour.
• The contour interval of a contour map is the difference in elevation between successive contour lines.

Deflection angle– An angle measured clock wise form the proceeding survey line to the next survey line.

Comparative scale–These are the scales having same representative fraction (R.F) but graduated to read different units.

• These scales may be plain scales or diagonal scales and may be constructed separately or one above the other.

Plain scale–Plain scale in one on which it is possible to measure two dimensions only such as units and length and diameters, miles and furlongs etc.

Diagonal scale–On a diagonal scale it is possible to measure three dimensions such as meters, decimeters and centimeters; unit, tenth and hundreds; yards; feet and inches.

Shrunk scale–If a graphical scale is not drawn on the plan and the sheet on which the plan is drawn shrinks due to variations in the atmospheric conditions.
• It becomes essential to find the shrunk scale of the plan.

Line of collimation–The line joining the intersection of the cross hairs to the optical center of the object glass.
• Line of collimation is perpendicular to the horizontal axis.
• Line of collimation is being parallel to the axis of the altitude level, when it is horizontal and vertical circle reads zero.

Hydrographic survey–It is conducted on or near water bodies marine survey is also one of its type.

Metallic tape– This is a linear tape woven into it longitudinally to reduce stretching.
• These are available in lengths of 20 to 30 m
• As it is reinforced with brass or copper wires, all the defects of linear tapes are overcome.

A tachometer is an instrument designed to measure the rotation speed of a shaft or disk. Tachometers generally measure rotations per minute (RPM) though some models also serve as rate meters and/or totalizers.

Given,
RL of point A = 201.100 m (Bench mark)
BS = 2.225 m
FS = 1.895 m
HI = RL + BS
= 201.10 + 2.225 - 203.325 m
Elevation of point B = RL of point B
RL of point B = HI – FS
= 203.325 – 1.895 = 201.430 m
Hence the elevation of point B = 201.430 m

The distance measured right or left of the chain line to locate details like boundaries, culverts etc. are called offsets.

These are of two types :
(i) Perpendicular offsets are right angles to the chain line.
(ii) Oblique offsets not at right angles to the chain line.