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KEJ. GEOMATIK

ECV 3501

Assoc. Prof. Dr. Ahmad Rodzi Mahmud

[email protected]

[email protected]

Credit to Dr. Helmi Zulhaidi Mohd Shafri

4. Angle Measurement

Outcomes:-

Understand and apply the concept measurement, traversing,

equipment used, plotting and accuracy

mailto:[email protected]:[email protected]:[email protected]:[email protected]
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Outline

Introduction

Units of angle measurement

Kinds of horizontal angles Bearing & Azimuths

Computation

Applications

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Introduction

Angles measured in surveying horizontal and vertical depending onwhich plane they are measured.

Useful for locating points anddetermining directions of lines.

Horizontal angles* to determine

bearings and azimuth. Bearings & Azimuth = Directions

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Introduction

Can be measured directly using compass, theodolite, total station andsextant.

Measured indirectly using tape method& geometric formulae.

3 basic requirements to determine anangle:

Reference / Starting line

Direction of turning

Angular distance (value of the angle)

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Basic requirements todetermine an angle

Angular

measurement

Direction of turning (+)

Target

North /Reference Line

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Units of angle measurement

Sexagesimal System: Degrees, Min,Sec

1 rad = 360/2 = 57.30

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Types of horizontal angles

Clockwise angles

Deflection angles

Bearings / Azimuths

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Direction of a line

In surveying, the direction of a line isdescribed by the horizontal angle thatit makes with a reference line.

This reference line is called aMERIDIAN or North Point.

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Meridian or North Point

Three types of meridians

Astronomic (or true) N-S reference

line through the Earths geographic

poles.

Magnetic direction taken by a magneticneedle at observers position.

Assumed arbitrary direction taken forconvenience.

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The North Pole

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True North Vs Magnetic North

1000 miles

4035

Magnetic Decl ineation

Grid

North

TRUE

(Astronomic)

North

Magnetic North

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Magnetic Declineation

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Azimuth Declineation in topomaps

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True North Vs Magnetic North

Today, the magnetic northpoleis located approximately

1000 miles south of the astronomic NorthPolein the

The compass needle lines up with magnetic north. In

most places this means that the needles points slightlyeast or west of astronomic north, depending on the

locality.

The angle between astronomic north and magnetic north

is referred to as the magnetic declination, which is 40

minutedeflected.

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Magnetic North - Shifted

The shifting is caused by liquidiron at the Earths core, whichis perpetually in motion. Thatmotion creates electric currents

in the core, which in turn,creates magnetic fields. Themotion of the Earths corechanges over time andtherefore, the planets magnetic

fields change as well.

Blue lines show Earth'snorthern magnetic field andthe magnetic north pole.

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Bearings

Two types:

Whole-circle bearing (WCB) or Azimuth

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A method of describing the direction of aline.

The QB of a line is defined as the smallest

angle which that line makes with thereference meridian.

A QB cannot be greater than 90.

- QB are measured in relation to the north

or south end of the meridian NE, NW,SE or SW.

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N

E

S

W

NW

SW

NE

SE

Y

X

Notes:

ie// xy : N 48 0000 E

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The reference meridian may be astronomic,magnetic or assumed.

Its convenient to say: N90E is due East

S90W is due West

Until the last few decades Americansurveyors favoured the use of QB.

With the advent of computers and

calculators, surveyors and engineersgenerally use WCB / azimuth instead of QB.

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WCB Bearing / Azimuths

0

90

180

270

Y

X

Notes:

ie// xy : 48 0000

CLOCK WISE ROTATION ! !

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Forward and Reverse WCB / Azimuth

Forward bearing XY = 480000

Reverse bearing XY or bearing

YX = 48 0000 + 180

Every line consists two direction.

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WCB / Azimuths

Orientation is synonymous withbearing from the surveyors point ofview.

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EquipmentCompass

Compass is always

showing the magnetic

poles. It is a wonderful

direction finder. The

earths magnetic field

and the use of thecompass have been

known to navigators

and surveyors for many

centuries

The compass was the

only means by which

the surveyor could

measure angles and

directions.

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Magnetic compass

For surveyors, however, the magneticcompass is not a true workmate.

It is not accurate enough, and is exposed

to disturbing effects. E.g. under theinfluence of iron objects

It may point to a direction which deviatesfrom the north to a high extent.

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Equipment- Transit / Theodolite - Total

Station

http://www.leica-geosystems.com/metrology/en/products/theodolites/lgs_788.htm
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- Theodolite +

gyroscope

- Determine the true

bearing

-Typically used in

mining surveyingand engineering

underground.

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Applications

Details maps or plans to describe aparticular site or area.

Setting-out of infrastructure.

Positioning of points or targets.

Many other important applications in

civil engineering and land surveying.

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House

Shed

Path

Tree

Trees

Angle-angle intersectionExample application - mapping

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Example Application - Settingout

e.g. determining the location of a new construction on a site

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Application - Mapping

House

Shed

Path

Tree

Trees

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Orientation /

Direction?

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Establishing orientation

Approximate orientationcan beestablished using a magneticcompass

A Certificate of Title showing thebearings of site boundaries could alsobe used

A professional surveyor could beengaged to undertake a cadastral(title) survey

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Certificate of Title

900000

100.045 m

100.045 m

2700000

1800

0

00

00

0

00

67.2

53m

67.2

53m

30.257 m

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Producing a plan

Choose a standard scale

Establish orientation

North up the page

Arbitrary Plot detail using protractor, compass,

scale ruler

Sharp, clean lines; neat, regular lettering

Or use a CAD or drawing package

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Exercise

Compute Q.Bearings given the Azimuth

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End of lecture