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

The ratio of torque to the weight of the moving part of an instrument is known as torque/weight ratio. It indexes the performance of the instrument. The higher value of torque/weight ratio shows that the instrument has good performances.

Methods of plane table surveying are–
1. Radiation
2. Intersection
3. Resection
4. Traversing

RF = Length of the object on map / Actual length of the object

• Since the length of the object on the map is always less than the actual length of the object, so the value of the representative fraction will always be less than one.

Ranging is the process of aligning the chain in a straight line between two extremities.

• The process of fixing or establishing intermediate points to facilitate measurement of survey lines are called as ranging. The intermediate point are located by means of ranging rods, offset rods and ranging poles

Theodolite - Theodolite is an instrument used for -
• Measurement of horizontal angle
• Measurement of vertical angle
• Measurement of horizontal distance
• Measurement of vertical distance

The theodolite has been the most used instrument for measuring horizontal and vertical angles since, at least, the sixteenth century when it was first described.
It consists of a telescope, mounted on a tripod that rotates 360⁰ around a vertical axis and vertically around a horizontal axis, which are perpendicular.

A vernier scale is good enough to read in two digits after decimal.
Least count of vernier calliper = 0.02 mm

L.C = Vernier scale / Main scale

R.F = 1/2500
1 cm = 2500 cm
1 cm = 25 m

Work from whole to part– The survey area is always totally covered with the simplest possible framework of high quality measurements.
It the rest of the survey work is carried out within this control, the possible accumulation of error can be contained and compensate error in a ways.