S2 a Lecture on Field Leveling

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.





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





Computations

Differential Leveling


http://slidepdf.com/reader/full/s2-a-lecture-on-field-leveling 4/17Elementary Surveying, 11e © 2006 Prentice-Hall, Inc.. 4/17


Computations


To check the accuracy of the work,

it is important to run closed circuit.




Computations





Computations


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.




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 ±=




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 =




Computations

Adjustment of Simple Level Circuits

The misclosure = +0.24 ft

Elevation adjustment = 0.24 ft / 3.0 per mi = 0.08 ft/mi




Computations

Profile Leveling




Computations

Profile Leveling

L li Fi ld P d d





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





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





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





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

S2 a Lecture on Field Leveling

Documents

Transcript of S2 a Lecture on Field Leveling