Geomatic Engineering Lab Compass Surveying Geomatic Engineering Lab

Prismatic Compass

True Meridian and Magnetic Meridian True meridian : A line or plane passing through the geographical north pole and south pole of any point on the earths surface Magnetic Meridian : When a needle is suspended freely and balanced properly, unaffected by any magnetic substance, it indicates a direction. This direction is called magnetic meridian.

True Meridian and Magnetic Meridian

Whole Circle Bearing [WCB] and Quadrantel Bearing [QB] WCB: the magnetic bearing of a line measured clockwise from the north pole towards a line is known as whole circle bearing of that line Such a bearing may have any value between 0° to 360° It can be obtained with the help of a prismatic compass

Whole Circle Bearing WCB of AB = θ1 WCB of AC = θ2 WCB of AD = θ3 WCB of AE = θ4

Quadrantel Bearing [QB] The magnetic bearing of a line measured clockwise or counter clockwise from the North Pole or SouthPole which ever is nearer the line towards East or West is known as Quadrantel bearing This system consists of four quadrants NE SE SW and NW The value of a quadrantel bearing lies between 0 to 90 degree. But the quadrants should always be mentioned

SURVEYOR COMPASS

Reduced Bearing [RB] When the whole circle bearing of a line is converted to quadrantel bearing it is termed as reduced bearing. Its value lies between 0° and 90° but the quadrants should be mentioned for proper designation.

Relation WCB between Corresponding RB Quadrant 0 and 90 RCB = WCB NE RB = 180- WCB SE 180 and 270 RB = WCB -180 SW 270 and 360 RB = 360 – WCB NW

Fore Bearing and Back bearing The bearing of a line measured in the direction of the progress of survey is called the forebearing [FB] of the line The bearing of a line measured in the direction opposite to the survey is called back bearing of the line. In the WCB system the difference between the FB and BB should be exactly 180°

Find the interior or included angles

Report No.3 [08-10-2017] Q1) Differentiate between true meridian and magnetic meridian with the help of a neat sketch Q2) What you mean by front bearing and back bearing Q3) Show a neat sketch of Prismatic compass and mark all the parts of it.

Q4) Find the fore bearings only