MEASURENT OF ANGLES & DIRECTIONS
True Meridians
Sometimes known as the
astronomic or geographic
meridian
Generally adapted as reference
line in surveying practice
This lines passes through the
Geographic North and South pole
of the Earth and the observers
position
Invariable thus, uses as reference
for making boundaries of land
MEASURENT OF ANGLES & DIRECTIONS
Magnetic Meridians
The fixed line of reference which lies parallel with the
magnetic lines of force of the earth
Its direction is defined by a freely suspended magnetic
needle of a compass held at the observers position and
it is usually a reference line for rough surveys
This is not parallel to the true north since they
converge at a magnetic pole
Magnetic pole location is not in fixed location, thus,
magnetic meridians is changes over time.
MEASURENT OF ANGLES & DIRECTIONS
Grid Meridians
This is a fixed line of
reference parallel to the
central meridian of a system
of plane rectangular
coordinates
The use of this meridian is
applicable only to the plane
surveys of limited extent
MEASURENT OF ANGLES & DIRECTIONS
Assumed Meridians
An arbitrarily chosen fixed line of reference which is taken
for convenience
Usually the direction from a survey station to an adjoining
station or some well-defined and permanent point
It is used only on plane surveys of limited extent since they
are difficult or maybe impossible to reestablished if the
reference point is lost or obliterated
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
TRUE NORTH
MAGNETIC NORTH
GRID NORTH
ASSUMED NORTH
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
TRUE NORTH
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
TRUE NORTH
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
MAGNETIC NORTH
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
MAGNETIC NORTH
Agonic Lines is the circle on earth
surface which passes through
geographic as well as the magnetic
pole of the Earth or line at every
point of which magnetic declination
is zero
Isogonic Lines these are lines
on earth surface joining the point
where magnetic declination is
same.
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
MAGNETIC NORTH
Declination is an angle lays
between True north and
magnetic north and is likewise
the gravitation changing with
different values at each position.
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
MAGNETIC NORTH
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
GRID NORTH
North point which is stablished by
lines on a map which are parallel to
a selected central meridian. It may
coincide with lines directed toward
true north.
ASSUMED NORTH
Used to portray the location of any
arbitrarily chosen north
MEASURENT OF ANGLES & DIRECTIONS
DESIGNATION OF NORTH POINTS
GRID NORTH
North point which is stablished by
lines on a map which are parallel to
a selected central meridian. It may
coincide with lines directed toward
true north.
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Direction of line is defined as the horizontal angle the
line makes with an established line of reference.
In surveying practice, direction may be defined by
means of:
• Interior Angle • Bearings
• Deflection Angle • Azimuth
• Angles to the Right
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Interior Angle
These are angles between adjacent lines
in a closed polygon
Exterior Angle
These are angles located outside a closed
polygon and are referred to as
explements of interior angles
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Deflection Angle
These are angles between a prolongation of the preceding
line, it may turn to the right or turn to the left
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Angles to the Right
These angles are measured clockwise from the preceding line
to the succeeding line. These angles are also referred to as the
azimuth from backline.
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Bearing
The bearing of a line is the acute
horizontal angle between the
reference meridian and the line.
Convert the angle 45º degrees to the corresponding minutes and seconds
=44º (1x60)’
= 44º 60’
= 44º 59’ (1x60)”
= 44º 59’ 60”
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Bearing
The bearing of a line is the acute horizonta
angle between the reference meridian anl
the line. d
Forward Bearing. The bearing of a line
observed in the direction in which the
survey progresses
Back Bearing. The bearing observed in
the same opposite to the direction of the
survey.
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Azimuths
The azimuth of a line is its direction
as given by the angle between the
meridian and the line measured in
clockwise direction from either the
north or south branch of the
meridian.
Azimuths are usually preffered over
bearing by most surveyors because
they are more convenient to work
with
This may range from 0 to 360 degrees
and letters are not required.
MEASURENT OF ANGLES & DIRECTIONS
DIRECTION OF LINES
Azimuths Forward and Back Azimuths
Any line in the earth’s has two azimuths-
forward and back azimuth depending on
which end of the line is considered. These
direction differ 180 degrees from each
other
To determine the back azimuth when the
forward azimuth is known, the following
rules are used.
Rule 1. If the forward azimuth is greater than
1800 , subtract 180 degrees to obtain the back
azimuth.
Rule 2. when the forward azimuth of a line is
less than 180 deg. , add 180 to obtain the
back azimuth
Drawing Bearings
A. N 45° E
N
45°
W E
B. N 30° W
N
30°
W E
S
Drawing Bearings
A. S 60° E
N
W E
60°
S
B. S 20° W
N
W E
20°
S
Converting Bearings to Azimuth
A. N 45° E
N
225°
45°
180°
W E
Azimuth = 180° + 45°
Azimuth = 225°
S
Converting Bearings to Azimuth
A. N 30° W
N
30°
180°
W E
Azimuth = 180° - 30°
150°
Azimuth = 150°
S
Converting Bearings to Azimuth
A. S 60° E
N
300°
360°
W E
Azimuth = 360° - 60°
60° Azimuth = 300°
S
