General principle of surveying| principle of surveying to work from

PRINCIPLE OF SURVEYING

1. To work from whole to the part

2. To locate a new station by at least two measurements(linear or angular) from fixed reference point.

According to the first principle

The whole area is first enclosed by main stations(i.e.controlling station) and main survey lines(i.e.controlling lines). The area is then divided into number of parts by forming well conditional triangle. A nearly equilateral triangle considered the best well considered triangle. The main survey lines are measured very accurately with a standard chain. Then the sides of the triangle are measured.

PURPOSE: The purpose of this process of working is to prevent accumulation of error.

According to the second principle

The new stations should always be fixed by at least two

measurements (linear or angular) from fixed reference

point.

Linear measurement refer to horizontal distance measured by chain or tape.

Angular measurements refers to a magnetic bearing or

horizontal angle taken by a prismatic compass or theodolite.

When you select two points in the field and to measure the distance between them. These can be represented on a paper by two points placed in a convenient position.From these initial point also known as reference point.

Locate a point such as C with respect to two reference points such as A and B.

(a) Distance AC and BC are measured and C is plotted as the intersection point of two arcs with centres A and B and radii the measured distance. This method is much used in chain surveying.

(b) Perpendicular CD and distances AD or BD measured and C is plotted by the use of set square. This method is termed as offsetting and is used for locating details.

(c) Distance AC and the angle BAC are measured and C is plotted by a protractor or trigonometrically. This method is used in traversing.

(d) Angle ABC and BAC are measured and c is plotted by a protractor or by solution of triangle ABC. This method is much used in traingulation for very extensive work.

(e) Angle BAC and distance BC are measured and C is plotted by protractor or traigonometrically. This method is of minor utility and is used in exceptional cases.

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