 In today's lecture, we are going to study the bearing of survey line and its classification. At the end of this lecture, the viewers will able to define the bearing of survey line. They can explain the different types of bearing and their uses and they can calculate the included angles of the given bearing system. The bearing of survey line is the horizontal angle made by the survey line with respect to any reference direction. Here if you observe this figure, the survey line OP is making the horizontal angle 48 degree with respect to the north direction. So the bearing of line is the horizontal angle with respect to any reference direction. In this figure, the reference direction is north direction. The bearing of lines is used to locate the direction of one line or one point with respect to the other point. These are the two types of bearings, true bearing and magnetic bearing. True bearing is the horizontal angle made by the true meridian. If you observe this figure here, the 67 degree is the bearing of line AB or you can say true bearing of line AB with respect to the true meridian. True meridian is the point of intersection of geographic north-south pole with reference to the surface of the earth. Magnetic bearing is the horizontal angle made by the survey line with respect to magnetic meridian. Magnetic meridian means it is the north and south pole direction on the prismatic compass. Prismatic compass will have the magnetic needle which will show the north and south. So the magnetic bearing is the angle measured with magnetic meridian. If you observe this figure, 67 degree is the true bearing and 102 degree is the magnetic bearing of survey line AB, forebearing and back bearing. Forebearing is the horizontal angle measured from station A to station B. If you observe the figure here, theta is the forebearing of line AB which will measure from station A to B and back bearing is the horizontal angle measured by the survey line with respect to north from station B to A. So if you see the figure in this, theta is the forebearing of line AB and beta is the back bearing of line AB. It means forebearing means it is station A to station B and back bearing means from station B to station A. The relation between forebearing and back bearing is the difference should be 180 degree. If the forebearing is less than 180 degree, the back bearing should be 180 degree plus forebearing and if the forebearing is greater than 180 degree, the back bearing should be 4 bearing minus 180 degree. So every time you should maintain or you should check the relation between forebearing and back bearing while solving the traversing or to calculating the bearings. Now included angle. Included angle means is the angle made by the two survey lines. If you see the figure number 5 here, angle A, B, C, D and E are the included angles means these are the angles if you observe angle A. This angle is made by two survey lines that is survey line AB and survey line AE. Here the included angles are less than 180 degree or greater than 180 degree. If you observe figure number 5, here all these interior angles which are nothing but included angles, these are less than 180 degree and if you observe figure number 6, here except angle D, all the included angles are less than 180 degree and the angle D is greater than 180 degree. So there may be the included angles less than 180 degree or greater than 180 degree. Now how to calculate the included angles? Here the bearing system is given it is the closed traverse system. First of all you have to draw the bearing of survey lines by using or you have to draw the traverse by using the bearings. Here the line PQ will have forebearing 41 degree 20 minute. So it is 41 degree 20 minute from north line QR 114 degree 30 minute. It is also with respect to the north direction. So by using the forebearing you have to draw the traverse. Then how to calculate the included angles? P, Q, R and S. Now to calculate the included angle P it is difference of back bearing of line SP and forebearing of line PQ. If you observe here back bearing of line SP means it is from station P to S it is 94 degree 30 minute and forebearing of line PQ is 41 degree 20 minute. So if you get the difference of these two you will get angle P. The next angle Q back bearing of line PQ is 221 degree 20 minute means it is from north direction 221 degree 20 minutes back bearing that is Q to P and forebearing of line QR is 114 degree 30 minute. If you get the difference of these two you will get angle Q. So here it is angle Q is equal to back bearing of line PQ minus forebearing of line QR same as you have to calculate angle R and angle S. Now you pause the video and try to calculate the included angles of given bearing system. These are the answers for the question. Whole circle bearing system. Whole circle bearing system is the angles are always measured from the north direction in clockwise. If you observe this bearing system here each bearing or each horizontal angle of respective survey line is measured from the north direction. So in whole circle bearing system the bearings of lines are measured with respect to north direction in clockwise only. So it can ranges 0 to 360 degree angles because we are measuring it from north direction so it will have 0 to 360 degree angles. Quadrant bearing system. It is also called as reduced bearing. Quadrant bearing it means the bearing of survey lines are measured with respect to nearest north and south pole. If you observe this bearing system here for station A the angle is shown with respect to north direction station B the angle is shown with respect to south direction. So in quadrant bearing system the angles are measured with respect to nearest north and south direction. Then conversion of whole circle bearing to reduced bearing. If you observe figure here the bearing of line is 132 degree from north. How to convert it? The north south pole will have 180 degree so if you subtract 132 degree from 180 degree you will get 42 degree. So you can represent it as 42 degree south east means south 42 degree east. It is the conversion of whole circle that is whole circle bearing is 132 degree. If you convert it into reduced bearing it will be south 42 degree east. Circle bearing. Here if you observe the figure number 13 the bearing of line is given as respect to south pole means it is south 42 degree east. If you convert it into whole circle bearing system you have to subtract from 180 degree means north and south pole will have 180 degree and if I subtract 42 degree from 180 we will get the angle 132 degree which is from north and south pole. So likewise you have to convert the reduced bearing to whole circle bearing system. These are the references used for the further study. Thank you.