traversing of survey

ahmadi khan

1. Week No.6
Surveying-I
Lecture No.8
B-Tech 2015
By:
Engr. Shams Ul Islam
Lecturer, Civil Engg. Department
CECOS University Peshawar

2. Traversing
Atraverseconsistsofaseriesofstraightlinesofknownlength
relatedtooneanotherbyknownanglesbetweenthelines.Thepoints
definingtheendsofthetraverselinesarecalledthetraversestations.
Traversesurveyisamethodofestablishingcontrolpoints,their
positionsbeingdeterminedbymeasuringthedistancesbetweenthe
traversestationswhichserveascontrolpointsandtheangles
subtendedatthevariousstationsbytheiradjacentstations.
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3. Types of Traverse
Therearetwotypesoftraverse
•Opentraverse
•Closedtraverse
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4. Open Traverse
Anopentraverseoriginatesatapointofknownpositionandterminates
atapointofunknownposition.
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5. Closed Traverse
A closed traverse originates and terminates at points of known positions.
When closed traverse originates and terminates at the same point, it is
called the closed-loop traverse.
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6. Method of traversing
Therearefourmethodsbywhichthedirectionofthesurveylines
aredeterminedareasfollow.
1.Bythechainangle
2.Bythefreeorlooseneedlemethod
3.Bythefastneedlemethod
4.Bythemeasurementofanglesbetweenthesuccessivelines.
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7. By the chain angle method/ chain traversing
Inthismethod,theentireworkisdonewithachain/tapeonlyand
theanglebetweenthesuccessivelinesismeasuredwiththechain.
Anglesfixedbythemeasurementsareknownaschainangle.
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Engr.Shams Ul Islam ([email protected])
Free or loose needle method
Inthismethod,anangularinstrumentsuchascompassor
theodolite,issetupateachofthesuccessivestationsandthe
bearingofeachlinesistakenwithreferencetothemagnetic
meridianandnotwithreferencetotheadjacentlines.

8. Fast Needle Method
Inthismethod,atheodoliteisusedtodeterminethebearingofeach
line.Thebearingoffirstlineismeasuredwiththemagneticmeridians
andthebearingofthesuccessivelinesarefoundfromthedeflection
angleorfromtheincludedangle.
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Engr.Shams Ul Islam ([email protected])

9. Method of measurement of angles
Inthismethod,atheodoliteisusedformeasurementofangles.The
horizontalanglesmeasuredinatraversemaybe
•Includedanglesor
•Deflectionangles(betweenthesuccessivelines)
Thisisthemostaccuratemethodandisgenerallyusedforlarge
surveysandaccuratework.
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Engr.Shams Ul Islam ([email protected])

10. Instruments for measurement of angles
Theinstrumentscommonlyusedare:
•Compass
•Theodolite
•Totalstation
•Boxsextant.
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Engr.Shams Ul Islam ([email protected])

11. Compass
Thecompassisaninstrumentusedformeasuringthebearing
i.e.theanglebetweenthemagneticmeridianandtheline.
Somespecialtypesofcompassusedinsurveyare:
•Prismaticcompass
•Lenseticcompass
•Troughcompass
•Surveyor’scompass.
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Engr.Shams Ul Islam ([email protected])

12. Bearing of line.
Thehorizontalanglebetweenthereferencemeridianandthesurvey
lineistermedasbearingofthesurveyline.
Differenttypesofbearingsare:
•Truebearing
•Magneticbearing
•Arbitrarybearing
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13. True Bearing
ThegeographicalNorthofearthisdifferentfromthemagnetic
North.Hence,theanglewhichthesurveylinemakeswiththe
truegeographicalNorthistermedastruebearingofthesurvey
line.
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14. MagneticBearing
Themagneticneedleofthecompassalwayspointstowardsthe
magneticnorth-south(N-S)directionindicatingearth’smagnetic
axis.Sincethisdirectionissameatalltheplacesontheearth’s
surface,itisuniversallyusedasthereferencedirection.Theangle
madebysurveylineinaclockwisedirectionwithreferenceto
magneticN-Slineistermedasmagneticbearingoftheline.The
valueofmagneticbearingrangesfrom0
o
to360
o
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15. Arbitrary Bearing
Itisthehorizontalanglewhichasurveylinemakeswithany
arbitrarymeridian,whichisanyconvenientdirectiontowardsa
permanentandprominentmarkorsignal,suchasaMosquespire
ortopofachimney.Suchbearingsareusedtodeterminethe
relativepositionoflineinasmallarea.
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16. Whole Circle Bearing (WCB)
Thecompletecircleofangularmeasurementstartswithnorthas0
o
andendsatnorthat360
o
.Thebearingoflinedirectlyobtainedby
magneticneedlerangingfrom0
o
to360
o
iscalledwholecirclebearing
asshowninFigure.
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17. Quadrental system
Inthissystem,thebearingofalineismeasuredclockwiseor
counterclockwisefromthenorthpointorthesouthpointwhichever
isnearertheline,towardtheeastorwest.Inthissystem,thebearing
isreckonedfrom0°to90°ineachquadrant.
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18. Reduced Bearing (RB)
Themoreconvenientwaytounderstandthedirectionofasurveyline
istorepresentthebearingonaquadrantalsystem.Theangleis
measuredwithrespecttoN–Slinetowardseastorwestasshownin
Figure.
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19. Relation between the whole circle bearing and the
Reduced bearing
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Case W.C.B BetweenRules for R.BQuadrant
I 0 and 90° =W.C.B N.E
II 90°and 180° =180°-WCB S.E
III 180°and 270° =WCB-180° S.W
IV 270°and 360° =360°-WCB N.W

20. Relation between the whole circle bearing and
the Reduced bearing
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Engr.Shams Ul Islam ([email protected])