Engineering Surveying -1 CE212 Compass Surveying

Engineering Surveying -1 CE212Compass SurveyingLecture2016, September 03-04Muhammad Noman

Compass SurveyingChain surveying can be used when the area to be surveyed iscomparatively is small and is fairly flat.But when the area is large , undulating and crowded with many details ,triangulation(which is the principle of chain survey) is not possible.In such an area , the method of Compass surveying is used.In Compass survey chain or tape is used for linear measurements andcompass is used for fixing direction.In compass freely suspended magnetic needle directs to north- southand the bearing of line is obtained by line of sight.

Traversing Traversing is that type of survey in which a number of connectingsurvey lines form the frame work and the directions and lengths ofthe survey lines are measured with the help of an angle measuringinstrument and a tape respectively. The routine of chaining and offsetting is the same as in chain survey Compass surveying is not recommended for areas where localattraction is suspected due to the presence of magnetic substanceslike steel structures, iron ore deposits, electric cables , and so on.

Types of TraverseThere are two types of Traverse:1. Closed TraverseA traverse is close when itcompletes a circuit and returnsto the starting point. Thestarting and end points are thesame. It is particularly suitablefor locating the boundaries oflakes, woods etc. It is used formoderately large area

Types of Traverse2. Open TraverseA traverse is said to be open or unclosed when it does not form aclose polygon. It consists of a series of lines extending in the samegeneral direction and not returning to the starting point. It is mostsuitable for the survey of long narrow strip of country e.g. Costline, road, railway etc.

MeridianMeridian is a line Joining NorthPole and South Pole.There are two types of Meridian1. True MeridianThe plane that passes throughtrue North Poles and True SouthPoles at the time of Observationis called True Meridian orGeographical Meridian

Meridian2. Magnetic MeridianThe direction indicated by amagnetic compass is called asmagnetic meridian.The angle which a line makes withthe magnetic meridian is called amagnetic bearing of the line orsimply bearing of a line.

Magnetic DeclinationThe difference between True Meridian and Magnetic Meridian is calledMagnetic Declination

BearingBearing is a Horizontal Anglemeasured from the NorthIf Bearing is measured from TrueMeridian than it is called TrueBearing and if it is measured fromMagnetic Meridian than it is calledMagnetic Bearing.There are two systems commonlyused to express the bearing. Whole circle system Quadrantal system

Whole Circle BearingIn this system the bearing of a linemeasured with the magnetic north inclockwise direction. The value of bearingthus varies from 0o to 360o.Its value varies from zero to 360 , increasingin clockwise direction. Zero is northdirection, 90 is east, 180 is south and 270 is west.

Quadrantal SystemIn this system the bearing of a line is measured eastwardor westward from north or south whichever is near.The directions can be either clock wise or anticlockwise depending upon the position of the line.The value of bearing thus varies from 0o to 90o.The quadrant of survey line is also mentioned after thenumerical value of the angle.There are 4 quadrant1St Quadrant NE2nd Quadrant SE3rd Quadrant SW4th Quadrant NW

Reduced BearingThe angle exceeding 90o is reduced to a value under 90o this is calledas reduced bearing (RB).CASEWHOLE CIRCLE BEARING (WCB)REDUCED BEARING (RB)QUADRANTI0 – 90WCBNEII90 – 180180 – WCBSEIII180 – 270WCB – 180SWIV270 - 360360 - WCBNW

Types of CompassesThere are two types of Compasses1. The Prismatic Compass2. The Surveyor’s CompassAssignment # 02

Problems: 01Convert the following WCBs to QBs:a)b)c)d)WCB of AB 45 30’WCB of AB 125 45’WCB of AB 222 15’WCB of AB 320 30’N 45 30’ ES 54 15’ ES 42 15’ WN 39 30’ E

Problem 02:Convert the following QB to WCBa) QB of AB S 36 30’ Wb) QB of AB S 43 30’ Ec) QB of AB N 26 45’ Ed) QB of AB N 40 15’ W216 30’136 30’26 45’319 45’

Problem 03:Q. The magnetic bearing of a line AB is 135 30’. What will be the truebearing, if the declination us 5 15’ W.A. True bearing of AB Magnetic bearing – Declination 135 30’ - 5 15’ 130 15’

Fore Bearing & Back BearingEvery line has two bearings one observed at eachend of the line.The bearing of the line in the direction ofprogress of the survey is called Fore Bearing (FB),while the bearing in the opposite direction iscalled Back Bearing (BB).Therefore BB of a line differs from FB by exactly180o.BB FB - 180oUse plus sign if FB 1800Use minus sign if FB 1800

Thank You

Sep 05, 2016 · Engineering Surveying -1 CE212 Compass Surveying Lecture 2016, September 03-04 Muhammad Noman. Compass Surveying Chain surveying can be used when the area to be surveyed is comparatively is