surveying bec102 3 - linear

8/13/2019 Surveying BEC102 3 - Linear

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Linear Measurement/Surveying

In these lectures we will cover:

The role of linear measurement

EquipmentProcedures and rules

Errors

Application of linear measurement /surveying


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Introduction

Distance is one of the most basic

engineering measurement.

Early measurement were made in terms of

dimension of the body

E.g. Foot, cubits, Pacing and Fathom


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Introduction

Being able to take accurate measurements and

record data are important science skills.

Students also need to know how to use math

formulas to convert different units of

measurement.

Geomatics provides real-world applications of a

variety of math and science skills


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Basic surveying measurement

5 basic quantities:

Slope distance AB, alongwith

Vertical angle BAB (orzenith angle AAB),

Horizontal distance AB =AB cos(BAB)

Vertical distance BB

Horizontal angle BAC also

needed to orient C relative toAB on the plot

B

B

A

c

A

C


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What is linear measurement?

Simple the measurement of distance:

New building site-

How big is it?

50.5 metres

27.9m

etres


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Errors in Measurement

Surveying measurement science:

All measurements contain errors

Identify sources of errors

Devise method of dealing with them


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Types of errors

BlundersMistakes and gross errors

Systematic errorsRepeated size and sign

Affect accuracy

Random errorsSmall and usually undetectable (noise)

Affect precision

These errors types

apply to any

measurement

technique used in

surveying


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Method of distance measurement

Distance Measurement

Direct

(length measurement)

e.g Measuring tape

Indirect

(distance measurement)

Geometrical(optical)

e.g tacheometry

Electronic(Wave Physics)

e.g EDM, GPS


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Tape measurements

For measuring lengths:

Measuring tape

Direct linear measurements

Cheap & robust

For small details


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Electronic Distance Measurement (EDM)


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Sources of error in EDM

PersonalCareless centering of instrument and or reflector

Faulty temperature and measurements

InstrumentalInstrument not calibratedElectrical center

Prism constant

Natural

Varying atmospheric conditionTurbulence in air


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Slope correction

Horizontal distance = h

To calculate horizontal distance:

H

h = s cos or h = (s2H2)1/2


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More advanced instrument

Total station

Theodolite, EDM, data processor & display unit

combined into one.

Provides instant data conversion into three-

dimensional coordinates & interface with

computers.


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Total station and prism

Ensure that the prism is properly

sighted & being held steady


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GPS measuring distances using

satellitesUse signal from GPS satellites to

determine positions (x,y,z coordinates).

Operated by the US Department ofDefense.

Need to use special receivers in order to

receive the signals.

Provides an efficient way of collecting data


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Methods and uses

Method Uses

Pacing Reconnaissance and rough planning

Stadia Mapping, rough surveys, checking more

precise work

EDM Geodetic survey and all types of survey

(e.g land survey and precise construction

work)

GPS Position determination locating control

points, all types of survey including

construction


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Application of distance measurement

Dimensions of building features

Block dimensions

Location and size of site featuresSetting out for construction

Clearances


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Importance of accurate measurement

Surveying measurement is related to the

work of civil engineers and architects,since an accurate survey is the first step in

land development and construction

projects.


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Negotiating obstructions

Weather

Buildings

LakeTree

mine


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Plotting the survey (AutoCAD)

Drawing unit Menu Format Units

Length type : select the Decimal

Precision : select 0.000 (three decimel.)

Angle type : select Deg/Min/Sec Precision : select 0d0000

Click on box : Clock Wise

Drawing units for DesignCentre Blocks When inserting blocks intothis drawing,scale them into : select Millimeters.

The next step, click on Direction box and you can see the displayDirection Control box.

Base Angle : select North.

Click : OK (direction control box)

Click : OK (Drawing units box)


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Another commandCommand : Cut Clip

Command : Zoom

Command : Move

Command : mirror

Command : erase

Command : Trim

Etc

Plotting the survey (AutoCAD)

surveying bec102 3 - linear

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