The following are the points of differences between prismatic and surveyor’s types of compasses. Difference # Prismatic Compass: 1. The graduated ring being attached to the magnetic needle remains stationary when the compass-box and the sight vane is rotated. 2. The graduations are marked on the ring in a clock-wise direction with 0° or 360" at South end of the [...]
There are two forms of the compass in common use: 1. The Prismatic Compass 2. The Surveyor's Compass. A compass is a small instrument which consists essentially of a magnetic needle, a graduated circle and a line of sight. When the line of sight is directed towards a line, the magnetic needle points towards magnetic meridian and the angle which [...]
The following two methods are generally adopted to find the areas from the previously plotted plans. The methods are: 1. Graphical Method. 2. Instrumental Method. 1. Graphical Method: In this method, the required data is obtained from measurements of the plan. The area may be found: (i) By the help of some geometrical figures or (ii) By the application of [...]
After reading this article you will learn about eight main precautions that should be taken while using a compass. Also learn about the sources of error in compass work. 1. The glass cover of the compass box gets charged with electricity when dusted off with a handkerchief or by the influence of electric charge in the atmosphere. Consequently, the needle [...]
The compass ring is graduated to half a degree but the readings can be well estimated to 15 minutes, which means that the error of reading should not exceed 7½ minutes. But due to magnetic changes and variation of declination etc., the readings can seldom be relied upon to less than 10 minutes, therefore, the permissible error per bearing should [...]
After reading this article you will learn about the meaning of bearing of a line and its designation with examples. Bearing of a line is the horizontal angle which a line makes with some reference direction also known as meridian. The reference direction may be any of the following: 1. A true meridian 2. A magnetic meridian 3. An assumed [...]
Bearings of lines may be calculated if bearing of one of the lines and the included angles measured clockwise between the various lines are given. Bearing of a line = given bearing + included angle. Note: In a closed traverse, where local attraction is not suspected i.e. difference between F.B. and B.B of all lines is exactly 180°, we can [...]
After reading this article you will learn about the field-work in compass surveying. 1. Field-Party: It will consist of four persons: (i) Surveyor for taking bearings of the lines, recording field-notes and imparting instructions to other party members. (ii) Two chainmen for chaining the survey lines. (iii) One flagman, cum pegman to fix stations, pegs and ranging rods as directed [...]
This article provides a note on local attraction along with its remedies and examples. The magnetic needle is disturbed from its normal position if it is under the influence of external attractive forces called the sources of local attraction. Such a disturbing influence is known as local attraction. The term is also used to denote the amount of deviation of [...]
This article throws light upon the six major problems in ranging and chaining of a line. Problem # 1. To erect, with a tape, a perpendicular to a chain line from a point on it: It can be done by forming a right angled triangle by taking three sides of a triangle in the proportion of 3, 4 and 5. [...]