leveling: field procedures and computationsmsu.ac.zw/elearning/material/1331196459cve202 lecture...

Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 1/17

Leveling: Field Procedures and Computations

Carrying and Setting Up a LevelAlways carry it in the container,Screw the head snugly on the tripod.For bull eye’s bubble, alternately turn one screw and then the other two.On side-hill setups, place one leg on the uphill side and other two on the down hill side.Use hand level to check for proper height of the setup before precisely leveling the instrument.



Duties of a RodpersonFor correct reading, the level rod must be held plumb.Using rod level, when the bull’s-eye bubble is centered the rod is plumbed in both directions.When a rod level is not available waving the rod is one of the procedure.

Plumping a level rod.Rod level



Differential Leveling




To check the accuracy of the work, it is important to run closed circuit.



Differential LevelingBalancing plus and minus sights distance to cancel errors caused by curvature of and refraction.

If D1 and D2 are made equal, collimation error e1 and e2 will cancel each other.



PrecisionPrecision in leveling is increased by

Repeating measurements,Using high-quality equipment,Keeping it in good adjustment, and Performing the measurements carefully.

No mater how carefully the work is executed, errors will exist.Various organizations set precision standards based on their project requirements.



PrecisionFor example, on a simple construction survey, an allowable misclosure of

where n is the number of setups.The Federal Geodetic Control Subcommittee (FGCS) USA recommends allowable misclosures

where C is the allowable loop misclossure, in millimeters, m is a constant, and K is the total length leveled in kilometers (for loops – circuits that begin and end on the same BM, K is total perimeter distance.

)(02.0 ftnC ±=

KmC =

)(6 mmnC ±=



PrecisionAllowable misclosure:

The FGCS specify different constants for the five classes of leveling.

First order class I m = 4 mmFirst order class II m = 5 mmSecond order class I m = 6 mmSecond order class II m = 8 mmThird order m = 12 mm

KmC =



Adjustment of Simple Level Circuits

The misclosure = +0.24 ftElevation adjustment = 0.24 ft / 3.0 per mi = 0.08 ft/mi



Profile Leveling



Sources of Errors in LevelingInstrumental Errors

Line of sightCross-hear not exactly horizontalRod not correct lengthTripod legs loose

Natural ErrorsCurvature of the earthRefractionTemperature variationsWindSettlement of the instrumentSettlement of a turning point



Sources of Errors in LevelingPersonal Errors

Bubble not centeredParallaxFaulty rod readingRod handlingTarget setting



MistakesImproper use of a long rod,Holding a rod in different places for the plus and minus sights on a turning point.Reading a foot too high.Waving a flat bottom rod while holding it on a flat surfaceRecording notesTouching tripod or instrument during reading process.



Reducing Errors and Eliminating MistakesErrors in running levels are reduced by

Carefully adjusting and manipulating both instrument and rod.Establishing standard filed methods and routines.The following routines prevent most large errors or quickly disclose mistakes:

Checking the bubble before and after each reading (if an automatic level is not being used).Using a rod level.Keeping the horizontal lengths of plus and minus sights equal.Making the usual field-book arithmetic checks

leveling: field procedures and computationsmsu.ac.zw/elearning/material/1331196459cve202 lecture...

Documents