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Surveying Techniques for Engineers

Fly leveling is an approximate form of leveling where sights are taken over long distances with less precision. The purpose is to quickly check reduced levels of existing benchmarks. Only backsight and foresight readings are taken without intermediate sights. Care must be taken in selecting change points and taking readings to ensure accuracy. There are three checks for errors in fly leveling: 1) closing the loop back to the beginning point, 2) using an equation to check calculations, and 3) allowable error or misclosure between known and computed points. The allowable error is based on a formula using distance and a constant, and any actual misclosure below this value means the survey is acceptable.

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Suman Jyoti
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114 views15 pages

Surveying Techniques for Engineers

Fly leveling is an approximate form of leveling where sights are taken over long distances with less precision. The purpose is to quickly check reduced levels of existing benchmarks. Only backsight and foresight readings are taken without intermediate sights. Care must be taken in selecting change points and taking readings to ensure accuracy. There are three checks for errors in fly leveling: 1) closing the loop back to the beginning point, 2) using an equation to check calculations, and 3) allowable error or misclosure between known and computed points. The allowable error is based on a formula using distance and a constant, and any actual misclosure below this value means the survey is acceptable.

Uploaded by

Suman Jyoti
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Prepared by

Lecturer: Razhan Sherwan


 Fly leveling: -It is a very approximate form of levelling in which sights are
taken as large as possible . in this method a line of levels is run to determine
approximately reduced levels of the points carried out with more rapidly and
less precision.

 The aim of fly levelling: The main purpose of this type of leveling
is to check the values of the reduced levels of the bench marks
already fixed. In this method only backsight and foresight are
taken. There is no need of intermediate sights. However great care
has to be taken for selecting the change points and for taking
reading on the change points because the accuracy of leveling
depends upon these.
1) Closed loop check To close the loop the survey is continued
back to the beginning. Any difference in elevation for BM1
between the initial elevation of BM1 and the closing
elevation of BM1 is error.

2) The Note check (The Computation check) The note check


uses an equation:
ΣB.S -ΣF.S = R.L last -R. L first

3) Allowable error (Misclosure):-Is the difference between the


known benchmark and computed benchmark
misclosure=Known point-Unknown point =0
 The third check for error is also called the allowable error.

 It is common practice for the individual contracting the work to


specify the acceptable level of error. Professional standards may
also specify allowable error.

The allowable error is based on an equation:


Allowable misclosure=E =C√𝑹

Where: C=constant C=12 for Mountain area C=30 for Ground


levelling
R= is total distance by Km

Correction= E/n n=Number of T.P stations


 If actual misclosure< allowable misclosure, therefore
the survey is acceptable. Unless, you divide the error
into turning points only.
 ΣBS - ΣFS only checks CALCULATION not
OBSERVATIONS
 Observationschecked by closing onto known final
point MISCLOSURE
 Intermediate sights NOT checked by either.

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