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 [...]
After reading this article you will learn about the meaning and variation of magnetic declination, with some examples. Meaning of Magnetic Declination: Except in few places, the magnetic meridian at a place does not coincide with the true meridian at that place. The horizontal angle which the magnetic mariotion makes with the true meridian is known as the magnetic declination [...]
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. [...]
The following are the five main methods of plotting a traverse survey: 1. By Parallel Meridians through Each Station 2. By Included Angles 3. By Central Meridian or Paper Protractor 4. By Rectangular Co-Ordinates 5. By Chords. Method # 1. By Parallel Meridians through Each Station: Having fixed suitably, the position of the starting point say A, draw a line [...]
The limit of length of the offset is below 15 and should not increase 15 m if its direction is set simply by eye or by tape. However, the length of offset mainly depends upon: (i) The scale of the plan (ii) The accuracy desired (iii) The maximum permissible error in eye judgement in laying out the direction of the [...]
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 the construction and classification of scale of a map. Construction of Scales of a Map: In plotting a survey, often an object to be represented on paper is so large that it would be inconvenient to make a full sized drawing of it. The drawing or map is then made to a [...]
The three main obstacles in chaining of a line are of the following types: 1. Chaining Free, Vision Obstructed 2. Chaining Obstructed, Vision Free 3. Chaining and Vision Both Obstructed. It sometimes happens that a survey line passes through some object such as a pond, a building, a river, a hedge etc. which prevents the direct measurement of that part [...]
The setting up of the plane table includes three operations viz: 1. Levelling 2. Orientation 3. Centering. Operation # 1. Levelling: Place the table over the station-point and spread out legs to make it level and at a convenient height, preferably not above the elbow. Then oriented and centre the table approximately as explained in the following two operations and [...]
There are two main types of the field-book: 1. Single Line Field-Book 2. Double line Field-Book. The field measurements, sketches and relevant notes are recorded for future reference in a note book, known as field-book. The field-book in general use is about 20cm * 12cm and opens length wise. Type # 1. Single Line Field-Book (Fig. 3.18, b): Every page [...]