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7/27/2019 S2 a Lecture on Field Leveling
http://slidepdf.com/reader/full/s2-a-lecture-on-field-leveling 1/17
Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 1/17
Leveling: Field Procedures and
Computations
Carrying and Setting Up a Level
Always 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.
7/27/2019 S2 a Lecture on Field Leveling
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 2/17
Leveling: Field Procedures and
Computations
Duties of a Rodperson
For 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
7/27/2019 S2 a Lecture on Field Leveling
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 3/17
Leveling: Field Procedures and
Computations
Differential Leveling
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Differential Leveling
To check the accuracy of the work,
it is important to run closed circuit.
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Differential Leveling
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Differential Leveling
Balancing plus and minus sights distanceto cancel errors caused by curvature of
and refraction.
If D1 and D2 are made equal, collimation error e1 and e2 will cancel each other.
7/27/2019 S2 a Lecture on Field Leveling
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7/27/2019 S2 a Lecture on Field Leveling
http://slidepdf.com/reader/full/s2-a-lecture-on-field-leveling 8/17Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 8/17
Leveling: Field Procedures and
Computations
Precision For 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 inkilometers (for loops – circuits that begin and end on thesame BM, K is total perimeter distance.
)(02.0 ft nC ±=
K mC =
)(6 mmnC ±=
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Precision
Allowable misclosure:
The FGCS specify different constants for the five classes
of leveling.
First order class IÆ m = 4 mm
First order class IIÆ m = 5 mm
Second order class IÆ m = 6 mm
Second order class IIÆ m = 8 mm
Third order Æ m = 12 mm
K mC =
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Adjustment of Simple Level Circuits
The misclosure = +0.24 ft
Elevation adjustment = 0.24 ft / 3.0 per mi = 0.08 ft/mi
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Profile Leveling
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Profile Leveling
7/27/2019 S2 a Lecture on Field Leveling
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Leveling: Field Procedures and
Computations
Profile Leveling
L li Fi ld P d d
7/27/2019 S2 a Lecture on Field Leveling
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 14/17
Leveling: Field Procedures and
Computations
Sources of Errors in Leveling
Instrumental Errors Line of sight
Cross-hear not exactly horizontal
Rod not correct length
Tripod legs loose
Natural Errors
Curvature of the earth
Refraction Temperature variations
Wind
Settlement of the instrument
Settlement of a turning point
L li Fi ld P d d
7/27/2019 S2 a Lecture on Field Leveling
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 15/17
Leveling: Field Procedures and
Computations
Sources of Errors in Leveling
Personal Errors
Bubble not centered
Parallax
Faulty rod reading
Rod handling
Target setting
L li Fi ld P d d
7/27/2019 S2 a Lecture on Field Leveling
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 16/17
Leveling: Field Procedures and
Computations
Mistakes
Improper 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 surface
Recording notes
Touching tripod or instrument during reading process.
L li Fi ld P d d
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Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 17/17
Leveling: Field Procedures and
Computations
Reducing Errors and Eliminating Mistakes
Errors 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 levelis not being used).
Using a rod level.
Keeping the horizontal lengths of plus and minus sights equal.
Making the usual field-book arithmetic checks