CHAPTER II
A FIELD REPORT ON
TRAVERSING
A REPORT BY RABI SHRESTHA
-frozenrabi28@gmail.com
1
Contents
1
2
Introduction ................................................................................................................... 5
1.1
Background ............................................................................................................. 5
1.2
Objective of project ................................................................................................ 7
1.3
Scope of work ......................................................................................................... 7
1.4
Technical terms ....................................................................................................... 7
Methods ...................................................................................................................... 10
2.1
Instrument used.................................................................................................... 10
2.2
Area of the project ................................................................................................ 10
2.3
Specification used for project ................................................................................ 10
2.4
Methodology ........................................................................................................ 11
2.4.1
Reconnaissance and planning ........................................................................ 11
2.4.2
Monumentation and D-card ........................................................................... 11
2.4.3
Angular measurement: .................................................................................. 12
2.4.4
Field computation: ......................................................................................... 12
2.4.5
Office computation: ....................................................................................... 14
2.4.6
Accuracy Assessment: .................................................................................... 14
2.4.7
Source of error: .............................................................................................. 14
3
Output, Analysis and Discussion ................................................................................... 16
4
Conclusion and recommendation: ................................................................................ 17
2
List of Tables
Table 1: Observed Horizontal Angle
Table 2 Observed Zenithal Angle
Table 3 Coordinates of Traverse Station
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List of abbreviations
B.B
Backbearing
Cg
centigun
Ccg
centicenti gun
DGPS
Digital Geographical positioning system
EDM
Electromagnetic Distance Measurement
FB
ForeBearing
RO
Reference Object
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1
Introduction
1.1 Background
Control survey is the art of establishing control point by considering shape and size of earth.

Horizontal control point: The control point which contains (x, y) coordinates i.e.
easting and northing. This control point can be established by traverse, triangulation,
trilatreration, intersection and resection.

Vertical control point: The control point which contain Z coordinate i.e. depth. This
control point can be established by levelling.

Full control point: Both horizontal and vertical control point can be established by
DGPS.
Principle
The principle of traversing is that if the direction and length of any line is known then the
coordinates of its head (end point) can be found from the given coordinates of its tail (starting
point).
Figure 1: Principle of traverse
Latitude (∆N) = l cos θ
Departure (∆E) = l sin θ
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If coordinate of A is known
Then coordinate of B can be calculated.
i.e. E2 = E1 + ∆E and N2 = N1 + ∆
Applicability of Traverse
 Traversing is based on the basic principle of surveying i.e. working from
whole to part.
 It forms the framework for tacheometric surveying.
 If coordinate and bearing of one traverse leg is known then other coordinates
can be determined.
 Area of the closed loop can be determined.
Order of traverse

First order traverse
 Highly precise traverse.
 Long range EDM is used for distance measurement and T2/T3 is used for
angle measurement.
 Used where second order triangulation is not possible.

Second order traverse
 It is controlled by primary traverse.
 Long range EDM is used for distance measurement and T2/T3 is used for
angle measurement.

Third order traverse
 It is conducted under controlled area of first order and second order traverse.
 It is used for cadastral survey.
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
Fourth order traverse
 It is conducted under controlled area of second order and third order traverse.
 It is used for engineering project.
1.2 Objective of project
The main Objective of the project was:
 To establish horizontal control points of fourth order in Pharsidol by method of
traversing.
The sub objectives of the project are:
 To provide framework for detailing.
 To learn the basics of fourth order Traversing.
 To measure horizontal and vertical angle.
 To know the method of preparation of description cards
 To established vertical control point by trigonometric leveling.
1.3 Scope of work
We had established 9 control points by the method of traverse which can be further used for
the densification of the control points. Also it can be used for the different kinds of survey
such as cadastral, topographical, and engineering and many more. It can also be used as a
framework for detailing. It can be used to calculate the area for engineering works.
1.4 Technical terms
Open Traverse: Either starts from known or unknown station and ends to another known or
unknown station. It is geometrically and mathematically open. It is suitable for long narrow
strips. But it is not preferred as it ends on unknown point, and hence checks cannot be
provided.
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Closed Traverse: It starts from known station and end to same station or another known
station. They are of two types:
 Closed loop Traverse: Starts from known station and end to same point. It is
geometrically and mathematically closed.
 Link Traverse: Starts from known station and closed to another known station. It is
geometrically open but mathematically closed.
Traverse station: Established station on connected line.
Traverse leg: Line joining two traverse stations.
Traverse Angle: Angle between two traverse legs, formed at a vertex/station.
Bearing: Horizontal angle between reference meridian and survey line which is measured in
clockwise and anticlockwise direction.
Fore Bearing (F.B): The bearing of a line in the direction of progress of survey is called F.B
Back Bearing (B.B): The bearing of a line in the direction opposite to the direction of
progress of survey is called B.B
Meridian: The fixed reference line about which bearing is measured is called meridian.
Index error: when the instrument in face left, the vertical circle should read 90˚or 270˚,
when the line of sight is horizontal, if it does not the deviation is known as index error.
Azimuth: True bearing of a line is azimuth.
Latitude: Projection on north south meridian.
Closing error: The distance by which Traverse loop fails to closed. This is denoted by e. It
occurs due to error in linear and angular measurement.
Angular misclosure: The difference between the sum of measured angles and the theoretical
sum of angles of closed traverse. The theoretical sum of interior included angles of close
traverse is (2n-4)*90, where n is the number of sides of closed traverse. The magnitude
permissible misclosure depends on the order of work.
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Included Angle : Clockwise angle between two successive Traverse Legs in horizontal
plane.
Zenithal Angle: Angle made by the Traverse line with the Zenith. It range from 0 º to 180 º,
with zero at zenith and 180º at nadir.
Adjusting traverse: Adjusting means to apply correction to latitude and departure, in order
to eliminate closing error.

Bowditch method: Also called compass rule. It is used to balance traverse where
linear and angular measurement are equally precise. By this rule, angular
measurements are inversely proportional to √l, where l is length of traverse leg.
Correction to latitude or departure = total error in latitude or departure ×
(length of that side / perimeter of traverse)
Thus, correction is applied in proportion of length in this method.

Transit method: This method is used where angular measurements are more precise
than linear measurement. The correction to latitude (or departure) of any traverse leg
should be proportional to the latitude (or departure) instead of the length of the
traverse leg itself.
Correction to the latitude of traverse = total error in latitude × (Latitude of
that traverse leg / Total Sum of latitudes)
Linear accuracy:
The ratio of closing error to perimeter of traverse is linear accuracy. It is expressed as 1:
n, which means that a closing error of 1m can be expected on carrying out that traverse to
a distance of n meters. The higher the value of n, higher is the relative accuracy.
EDM:
The
measurement
of
distance
by
using
electro-magnetic
wave
is
EDM(Electromagnetic distance measurement). In the electronic method of measuring
distances, the instruments rely on emission, propagation, reflection, and subsequent
reception of either light or radio waves.
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2
Methods
2.1 Instrument used
 Wooden pegs
 Ranging rod with tripod
 Theodolite with tripod
2.2 Area of the project
The project area is located at Lalitpur-22, Pharsidol. It covers area of Mass Nepal which
includes natural and man-made features like road, houses, ponds, playing ground etc.
2.3 Specification used for project
Order of work: Fourth order
Type of traverse: Closed loop traverse
Numbering: fourth order numbering (2000,1000-1008)
Angular unit: Degree, minute, second
Linear unit: meter
No. of sets: 3(000,060,120)
Distance: Single (one way)
Least count: 1” (angle)
Least count: 1mm (distance)
Angular observation: Theodolite(J2-2)
Distance observation: Total station
Face to face tolerance: 2 cg
Index error tolerance: 5 cg
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Set to set tolerance: 60 ccg
RO to RO tolerance: 30 ccg
Linear accuracy: 1:10000
Angular accuracy: 75√n ccg
Angle adjustment: Equal shift
Linear adjustment: Bowditch method
2.4 Methodology
2.4.1 Reconnaissance and planning
During planning, available instrument resources, human resources, purpose of survey
was kept on the mind. The area to be surveyed was examined by walking over the
entire area. During the reconnaissance, the intervisibility between two stations was
checked. Traverse station was not kept near the root of tree, river side, land slide area
.Traverse leg was not kept as longer as possible, shorter leg produce bisection error in
angle. So, ratio between longest leg and shortest leg in a particular traverse was kept
within 2:1.
2.4.2 Monumentation and D-card
All the control points selected on the reconnaissance phase were monument
with the help of marked wooden pegs. The distance between the three
reference permanent structures was measured and noted.The reference sketch
of particular area was prepared. Hence, it helps to relocate or find the station
in the entire area. Information like grid sheet no, station name and number,
type of monument and its diagram, field sketch, location( district, VDC,
ward), land owner, local representative, visible station number and name,
witness marks with direction and dimension, sketch and description to reach
the station.
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2.4.3 Angular measurement:
 Horizontal angle measurement: Three sets observation were taken in
000˚10’00”, 060˚10’00”, 120˚10’00”.
RO was taken on previous
station and exterior angle was measured between RO and next station,
finally RO was closed. To eliminate collimation error, both face left
and face right observation were taken.
 Zenithal angle measurement: Only one set observation was taken in
any set while observing horizontal angle. As like in horizontal angle
measurement, to eliminate index error, both face left and face right
observation were taken. The index error was then distributed equally to
both face left and face right reading to get corrected zenithal angles.
Linear measurement:
 EDM (Electromagnetic distance measurement) instrument was used for measuring
distance between two consecutive traverse legs.
2.4.4 Field computation:
Horizontal Angle: Mean value of face left and face right observation was calculated.
Opening and closing mean reading of RO was compared , if it lies within tolerance of 30 ccg,
necessary reduction to make 000˚10’00” to 000˚00’00” was done in each set and mean value
of three sets was taken as the observed value.
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Station
FACE
Horizontal Readings
Set I
From
TO
1000
1008
2000
Horizontal Angle
Mean
D
M
S
M
S
D
M
S
L
000
10
00
10
06
R
180
10
11
00
00
L
169
33
01
33
03
169
22
57
R
349
33
05
22
57
169
22
56
L
000
10
00
10
08
R
180
10
16
00
02
-1
-02
000
00
02
Table 1: Observed Horizontal Angle.
Zenithal Angle: Sum of face left and face right observation was calculated. If it was not
equal to 360˚ correction on face left and face right was applied using equal shift. Corrected
face left value and corrected face right value was noted.
Zenithal Reading
Height of Target
D
M
S
Z
( meter)
103
29
50+13
359˚59’34”
1
256
29
38+13
103˚30’03”
1
076
43
53+22
359˚59’16”
1
283
15
23+22
076˚44’15”
1
Table 2: Observed Zenithal Angle.
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2.4.5 Office computation:
Bearing of next line= bearing of previous line+ exterior angle of previous line with next line
± 180˚/540˚.
Sum of exterior angles of a polygon= [(2n+4)*90] degree.
Angular misclosure = Calculated value of Sum - Sum of interior angles of a Polygon.
Correction in exterior angle =Angular misclosure / Total no of angles.
Closing error =√[(sum of latitude)²+(sum of departure)²]
Bowditch rule was used to balance traverse as linear and angular measurement were equally
precise.
According to the Bowditch rule:
Correction to latitude or departure = total error in latitude or departure × (length of that side /
perimeter of traverse)
2.4.6 Accuracy Assessment:
Angular misclosure = Calculated value of Sum - Sum of interior angles of a Polygon.
Closing error =√[(sum of latitude)²+(sum of departure)²]
Relative closing error= closing error/perimeter of traverse
Direction of closing error (A) = tan-1(sum of departure/sum of latitude)
2.4.7 Source of error:

Error due to inaccurate centering:-If the center of theodolite does not coincide with
the ground station mark, the horizontal angles measured at this station are affected
with an error, known as centering error. This error depends on the distance between
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theodolite center and ground station mark. This error varies inversely with length of
the sight. It is eliminated by accurate centering.

Error due to inaccurate leveling:-Inaccurate leveling introduces serious error in
horizontal angle and zenithal angle measurement. This error can be eliminated by
accurate leveling of both bubbles.

Collimation error:-If the axis of telescope is not parallel to the line of collimation, this
error is introduced. This error can be eliminated by taking mean of two face left and
face right observation.

Index error:- When the instrument in face left, the vertical circle should read 90˚or
270˚, when the line of sight is horizontal ,if it does not the deviation is known as
index error. This error is eliminated by taking face left and face right observation.

Error due unequal graduation:- If the graduation of the lower plate are unequal , the
observed angle on different portion will be apparently different. This error can be
minimised by measuring the angles on different zeros and taking mean of all values of
the angle.
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3
Output, Analysis and Discussion
The Co-ordinates of traverse stations calculated were:
Station
Easting(m)
Northing(m)
Reduced Level(m)
2000
628015
3056145
1273
1000
628023
3056046
1250
1001
628122.99
3056099.047
1270.961
1002
628153.69
3056014.793
1257.874
1003
628243.261
3055918.881
1245.158
1004
628134.901
3055799.547
1224.351
1005
628106.765
3055724.218
1222.433
1006
628017.501
3055837.697
1219.216
1007
627995.474
3055925.022
1224.444
1008
628015.940
3055978.821
1234.765
1000
628023
3056046
1250
Table 3: Co-ordinates of traverse stations
Closing error= 0.044 m
relative accuracy = 1:21255
Direction of closing error = 1˚18’7.03”
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4
Conclusion and recommendation:
Hence, using the method of theodolite traversing, 9 control points were established. The
closing error of our loop was calculated as 0.044 m with relative accuracy of 1:21255. The
control points so obtained were used as framework for tacheometric surveying.
**Field books containing data of Traversing are attached in annexes.
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