Fundamental Principles of Surveying

There are two fundamental principles of surveying which should be taken into consideration to get good results.

1) Working from whole to part

Working from whole to part is achieved by covering the area to be surveyed with a number of control points called primary control points whose pointing have been determined with a high precision equipment. Based on these points, a number of large triangles are drawn. Secondary control points are then established to fill the gaps with lesser precision than the primary control points. At a more detailed and less precise level, tertiary control points at closer intervals are finally established to fill in the smaller gaps. According to the first principle, the whole survey area is first enclosed by main stations (i.e. control stations) and main survey lines. The area is then divided into a number of divisions by forming well conditioned triangles.

Fig. 1 Working from whole to part - Representation

The main purpose in survey to work from whole to part is to localize the errors. During measurement, if there is any error, then it will not affect the whole work, but if the reverse process is followed then the minor error in measurement will be magnified. In partial terms, this principle involves covering the area to be surveyed with large triangles. These are further divided into smaller triangles and the process continues until the area has been sufficiently covered with small triangles to a level that allows detailed survey to be made in a local level.

2) Using measurements from two control points to fix other points

According to the second principle the points are located by linear or angular measurement or by both in surveying. If two control points are established first, then a new station can be located by linear measurement. Given two points whose length and bearings have been accurately determined, a line can be drawn to join them hence surveying has control reference points. The locations of various other points and the lines joining them can be fixed by measurements made from these two points and the lines joining them. For an example, if A and B are the control points, the following operations can be performed to fix a new point C.

Fig. 2 Location of the third point from the position of two known points

1. The distance AB can be measured accurately and using points A and B as the centers, ascribe arcs using distances d1 and d2, then fix point C (where they intersect).
2. Draw a perpendicular from AB to a point C.
3. Taking one linear measurement from B and one angular measurement as <ABC
4. Taking two angular measurement at A & B as angles < CAB and <ABC.
5. Taking one angle at B as < ABC and one linear measurement from A as AC.