“ COMPASS SURVEY ”

                   “ COMPASS SURVEY ”

INTRODUCTION:-

·       DEFINITION:- Compass surveying is a type of surveying in which the directions of surveying lines are determined with a magnetic compass and the length of the surveying lines are measured with a tape or chain or laser range finder.

·       TRAVERSING:-

1.  CLOSE TRAVERSE:- When a series of connected lines form a closed circuit, which finishing point coincides with the starting point of a survey is known as closed traverse.

2.  OPEN TRAVERSE:- When a sequence of connected lines extend along a general direction and do not coincide with the starting point is known as open traverse.

·       BACK BEARING(BB):- The bearing of the line measured in the direction opposite of the survey is Back Bearing.

·       FORE BEARING(FB):- The bearing of the line measured in the direction of the progress of the survey is known as Fore Bearing of the line.

·       WHOLE CIRCLE BEARING(WCB):- The magnetic bearing of a line measured clockwise from the north pole towards the line. Its value lies between 0˚ to 360˚.

·       REDUCED BEARING:- When the whole circle of a line exceeds 90˚, it must be reduced to the corresponding angle less than 90˚, which has the same numerical value of the trigonometrical functions. This angle is known as the Reduced Bearing. Its the value lies between 0˚ and 90˚.

·       LOCAL ATTRACTION:- A magnetic needle indicates the north direction. But if the needle comes bear magnetic substance such as iron, steel structure, electric cables conveying current, etc, it is deflected from its true direction and does not show the actual north. This disturbing influence of magnetic substances is known as “ Local Attraction”.

·       DIP:- If the needle is perfectly balanced before magnetization, it remains in the horizontal position. But it will not remain in the same position after it is magnetized, on account of the magnetic influence of the earth. It will be inclined downwards towards the pole. This inclination of the needle with the horizontal is known as Dip of the needle.

 ·       DECLINATION:- The horizontal angle between meridian and true meridian is known as declination.

video link:-compass survey 2nd part