Traverse

Control Survey - Traversing*CONTROL SURVEYControl the principle of tying measurements together in such a way as to produce a survey which is accurate in proportion and scale.The form of control to be provided depend on the type of survey and the accuracy demanded.Control consists of traverse survey, triangulation or trilateration, GPSControl survey provides a framework of survey points whose relative positions are known.

Control Survey - Traversing

Control Survey - Traversing*Traverse surveyMost economical methodProvide a higher standard of accuracy of control in terms of time and moneyWidely usedFlexible method of providing control for site surveys


Control Survey - Traversing*Traverse surveyDefinitionsTraverseA series of consecutive lines whose lengths and directions have been determined from field measurements. Lines are known as legs and end points pf the lines as stations.TraversingThe act of establishing traverse stations and making the necessary measurements


Control Survey - Traversing*Types of Traverse and classificationClosed Traverse1. Loop. The lines starts and finish on the same point.2. Link. The lines close on a point of known position.Open TraverseThese commence at a known point and finish at an unknown point.Generally be avoided.Traverse may be classified by the accuracy attained typically precise, semi precise or low accuracy.

Precise - An accuracy of greater than 1:10000 is expected.Semi precise - An accuracy of up to 1:10000 or better.Low accuracy an accuracy less than 1 : 5000


Control Survey - Traversing*Closed TraverseClosed traverses provide checks on the measured angles and distancesBecause of this ability to check the measurements and the results mathematically adjusted, closed traverses are more desirable.


Control Survey - Traversing*Appropriate uses of traversingTraverse survey will be a suitable method if:Control is to be provided for a site surveyTape and offset linear survey techniques are inadequate to meet the taskThe accuracy demanded is grater than can be achieved by tape and offsets surveyThe introduction of traversing into tape and offset will reduce the cost and the duration of the job


Control Survey - Traversing*Traversing FieldworkChoose suitable equipment and the accuracy requiredCarry out a reconnaissance. Choose stations positions carefullyBuild, protect and witness stations. Prepare the witnessing stationsMeasure each traverse legs at least twice once in each directions.Measure each traverse angle. Take at least 2 rounds at every station


Control Survey - Traversing*Traverse ComputationsPrepare a traverse abstract. Sketch showing all measurements LHAs and distances, starting data and direction of workingEnsure angles are closeCalculate WCBsCalculate the coordinate differencesCalculate the traverse accuracyIf acceptable distribute misclosureCalculate the final coordinates


Control Survey - Traversing*1. Traverse AbstractAll lengths corrected and reduced to horizontalAll angles are mean observed LHAsGiven Data: WCB AF = 70 00 00Coordinates of A = 500.00 mE, 1000.00 mN


Control Survey - Traversing*2. Ensure that the angles closeIn polygon traverse, angular misclosure are found by comparing the observed angles with one of the following theoretical valueSum of internal angles = (2n - 4) x 90Sum of external angles = (2n + 4) x 90


Control Survey - Traversing*Allowable Angular MisclosureThe allowable misclosure is given by

where K is a multiplication factor of 1 to 3S is the smallest reading interval on the theodolite in secondsn is the number of angles measured


Control Survey - Traversing*Adjustment When the actual misclosure is known and is compared to its allowable value, two cases arises:1. If misclosure is acceptable (less than its allowable) it is divided equally between observed angles2. If its greater than allowable then angles should be re-measured if no gross error can be calculated in the angle booking.


Control Survey - Traversing*3. Calculate WCBsThe forward WCBs of all traverse legs are required.

Forward Brg. YZ = Back Brg. YX + LHA at Y and in general :Forward Brg. = Back Bearing + LHAThe forward Brg. of a line differs from its back by 180


Control Survey - Traversing*4. Calculate Coordinate DifferencesE = D. Sin N = D. Cos represent the WCB of the line.


Control Survey - Traversing*5. Calculate the traverse accuracyFor a Polygon traverse (theoretically) E = 0 and N= 0Misclosure in Easting =eE = EMisclosure in Northing =eN = N

Linear misclosure = e = (eE2 + eN2)Fractional Linear Misclosure = FLM = 1 in (D/e)


Control Survey - Traversing*6. Distributing Linear misclosureIf the misclosure is acceptable then distributeBowditch Method - proportional to leg distancesTransit Method proportional to E and Northing ValuesEqual Adjustment


Control Survey - Traversing*7. Calculate the final coordinatesThe adjustments are applied to the original partial eastings and partial northings values to give the Adjusted partial eastings and partial northings values.Starting from the initial known coordinates the Adjusted partial eastings and partila northings are applied in turn from station to station to give the final coordinates.As a check final coordinates of the known finish station are calculated and they must agree exactly with the known values.


Control Survey - Traversing*Traverse plottingDraw an accurate coordinate grid at the required scalePlot the traverse stations. Scale equal distances along the grid linesJoin the stations to form traverse linesMeasure these as a check


Traverse specificationGeneral - general engineering work include site surveying and setting out1 in 5000 to 1 in 50000(angular measurement) Electronic theodolite or total station (distance measurement) Total station or steel

Control Survey - Traversing*


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Traverse

Documents

framework of survey

gpscontrol survey

type of survey

linear survey techniques

traverse stations

traverse legs

types of traverse

traverse computationsprepare