Surveying (Part-2) (General Engineering) (SSC JE)

The angle of intersection of a contour and a ridge line, is 90°.
Ridge line–A ridge line is a line of high ground, with the land dropping away either side. Ridges are common between two hill tops.

Satellite–A satellite is any body revolving around a large body under the influence of later. An artificial satellite or communication satellite of earth is one which appears satellite of earth is one which appear stationary to an observer on the earth's surface.

• An artificial satellite is also known as a geostationary satellite or geosynchronous satellite.
• The orbit of the satellite must be circular and in the equatorial plane of the earth.

Collimation method–
1. Collimation method is most suited for longitudinal or cross-section levelling.
2. In rise and fall method the check for intermediate reading is done using ΣRise – ΣFall.
3. Reduction is easier with the height of collimation method.
4. Rise fall method is well suited for determining the different of level of two points.
5. Arithmetic check for HI method–
ΣBS – ΣFS = Last RL – First RL

Tachometers– Tachometers are generally used to measure the rotation speed of a shaft or disk as in a motor or other machine.

• There are two types of tachometers namely the Fullerton tachometer and Frahm tachometer which are used to measure the frequency of the vibration system.

• The working of frequency measuring instruments is based on the principle of resonance.

• At resonance, the amplitude of vibration is found to be maximum and then the excitation frequency is equal to the natural frequency of the instruments.

Chain surveying is adopted for preparing plans of small areas.

Chain surveying is recommended when-
(i) The ground surface is more or less level.
(ii) A small area is to be surveyed.
(iii) A small-scale map is to be prepared.
(iv) The formation of well conditioned triangle is easy.

Contour line– Contour is an imaginary line joining points of equal elevation on earth surface.

Contour interval–Vertical distance between two consecutive contour is called contour interval.

• The four bar mechanism with all its pairs as turning pairs is called the quadric cycle chain.
• When one of these turning pairs is replaced by a slider pair, the chain becomes single slider chain.
• When two turning pairs are replaced by slider pairs, it is called a double slider chain or a crossed double slider chain, depending on whether the two slider pairs are adjacent or crossed.

Magnetic bearing– The magnetic bearing of a line is the horizontal angle which it makes with the magnetic meridian passing through on of the extremities of the line.

Survey stations–
• A survey station is a prominent point on the chain line and can be either at the beginning of the chain line or at the end.
• A survey station may be marked on the ground by driving pegs if the ground is soft. However on roads and streets etc.
• The main lines should form well-conditioned triangles.
• As far as possible the main survey lines should not pass through obstacles.

Total station is an electronic/optical instrument used in modern surveying angles and surveying distance are measured from the total station to points under survey and the co-ordinates of surveyed points relative to the total station position are calculated using triangulation. In case of plane, width of a river can be measured by triangulation property of total station.

• Microprocessor unit in total station is used for the computation of data collected. Various instrument and its use–