Angle Measurment a.pdf

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KEJ. GEOMATIK
ECV 3501
Assoc. Prof. Dr. Ahmad Rodzi Mahmud
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
Centesimal System: Grad
European Radians rad = 180 degrees
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) NS 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
Canadian artic near Bathurst Island.
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:
Quadrant bearing (QB)
Wholecircle bearing (WCB) or Azimuth

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Quadrant Bearings
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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Quadrant Bearing
N
E
S
W
NW
SW
NE
SE
Y
X
Notes:
ie// xy : N 48 0000 E

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Quadrant Bearings (QB)

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Quadrant Bearings
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.leicageosystems.com/metrology/en/products/theodolites/lgs_788.htm 
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Advanced equipment Gyrotheodolite
 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.
Settingout of infrastructure.
Navigation.
Positioning of points or targets.
Many other important applications in
civil engineering and land surveying.

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House
Shed
Path
Tree
Trees
Angleangle 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
Government Road
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