Traverse Survey

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With Wisdom, We Explore

TRAVERSE SURVEY

Mohd Effendi Daud (Dr. Sc)B.Surv (UTM, Malaysia) Msc (UTM, Malaysia), Dr.Sc, (Nagoya Univ., Japan)

(Geomatic Division)Faculty of Civil & Environmental Engineering,

Universiti Tun Hussein Onn Malaysia, 86400 Batu Pahat, Johor, MALAYSIA.Phone : +6074537363; +60197853740; Fax : +6074537060

E-mail : [email protected]: http://www.fkass.uthm.edu.my/

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OVERVIEW

Learning outcomes

By the end of this topic you should be to: Outline the basic components of a Total Station,

Carry out temporary adjustments of a TS,

Compute and adjust a TS traverse,

Compute coordinates for traversing, and

Determine the nature of errors affecting the traverse work.

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INTRODUCTION

Traversing is a form of a control survey that requires the establishment of a series of stations that are linked together by angles and distances.

The angles and distances are measured by Total Station.

The use of traversing surveys is very fundamental and has become one of the most common methods in geomatic engineering work such as:

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INTRODUCTION

General purpose angle measurement,

Provision of control surveys,

Contour and detail mapping, and

Setting out and construction work.

This topic will describe:-

The construction and use of the Total Station in traversing,

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INTRODUCTION

The traverse design and the procedures of computing and adjusting a traverse,

The application of coordinates for point will also be covered in this topic which will be very useful in Civil Engineering project.

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A total station is an electronic/optical instrument used in modern surveying.

The total station is an electronic theodolite integrated with an electronic distance meter (EDM) to read distances from the instrument to a particular point.

A theodolite is an instrument for measuring both horizontal and vertical angles. It is key tool in surveying and engineering work.

TOTAL STATION PRINCIPLES & APPL

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Vertical angles are required for the calculation of elevation of points for example the reduction of slope distance to the horizontal.

Horizontal angles are required to obtain the relative direction to a survey control station or points of detail.

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Construction of a Total Station

All total station have the same common features which is can be described as follows.


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Temporary Adjustment of Total Station

The temporary adjustments are steps that must be carried out every time a total station used.

It is a procedure of setting up a theodolite that involves the following process

Centering

Leveling, and

Removing parallax.


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(a) Centering the total station

The instrument must be vertically above the survey station to ensure that horizontal angle observation are correct.

The steps are as follow: Start with a optical plummet to get it

approximately right above the survey station.

Using the foot screws, move the optical plummet cross hairs on the survey station.


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(a) Centering the total

stationcont. Roughly level the instrument

using legs of the tripod the total station should stay almost on target.

Level with foot screws. Move instrument above target; repeat level and move until done.


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(b) Leveling the Total Station Turn bubble parallel to two foot screws A and

B, to bring the horizontal bubble to the centre.

Turn the instrument through 90 and bring the bubble to the centre by adjusting the third foot screw C only.

Turn the instrument through a further 90 to check the adjustment of the plate bubble.


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(b) Leveling the Total Station cont.

If the bubble remains in centre, then it is adjusted.

If not, repeat the whole procedure.


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Permanent Adjustment of Total Station

These adjustment are carried out once and will not alter unless it is being roughly handled or tampered with.

There are certain basic requirements for a total station that must be established particularly when using it.

The basic requirements re as follows:


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The vertical axis of a total station should be truly vertical,

The line of sight should be perpendicular to the horizontal axis,

The horizontal axis should be truly horizontal,

The cross hair should be truly vertical and horizontal, and

The vertical circle should be at zero when the line of sight is horizontal.

** The steps in carrying out the adjustments should be handled by the qualified person at the laboratory **


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ANGLE MEASUREMENT

Horizontal Angle Measurement

The concept of measuring the horizontal and vertical angle is simple.

The following procedures should be used to measure the horizontal angles between three stations A, B, and C

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Setup the total station on station B. the total station instrument has two faces; Face left & Face right.

Starting from the face left, the telescope is pointed at station A. The horizontal reading is then noted, i.e. 253000

ANGLE MEASUREMENT

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The instrument is then turned in a clockwise direction to point at station C. Again the horizontal reading is noted, i.e. 1455000

The horizontal angle can be calculated, by finding the difference between the two horizontal reading.

ANGLE MEASUREMENT

i.e., C A = 1455000 25o3000 = 1202000

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Change the face of the total station. Whilst pointing at station C the horizontal reading is again recorded, i.e. 3255000

Turn the instrument in a clockwise manner and point at station A. Record the horizontal reading, i.e. 2053000.

ANGLE MEASUREMENT

i.e., C A = 3255000 2053000 = 1202000

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Note that changing the face will change the reading by 180. This gives a check on the observations and ensures that reading errors can be eliminated. If there is a great difference in two readings, the observations are repeated until readings agree.

ANGLE MEASUREMENT

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Vertical Angle Measurement

A vertical angle is the angle measured vertically from a horizontal plane of reference.

When the telescope is pointed in the horizontal plane (level), the reading of the vertical angle is zero (0).

ANGLE MEASUREMENT

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When the telescope is pointed up, then the vertical angle increases from zero and the reading is a positive (+ve) vertical angle. The reading increase from 0 to +90when the telescope is pointed straight up.

ANGLE MEASUREMENT

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If the telescope is depressed (pointed down), then the angle reading will increase in numerical value. The depressed telescope reading indicates that it is below the horizontal plane and the reading is a negative (-ve) vertical angle. These numerical value increase from 0 to -90 when the telescope is pointed straight down.

ANGLE MEASUREMENT

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TRAVERSE & COORDINATE SYSTEM

Traverse Definition

A traverse is a series of straight lines that are used to connect a series of selected points. This selected points are called traverse stations where distance and angle measurements are made. The relative positions of the traverse stations are then computed using some coordinate systems.

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For a better understanding, the definition of traverse survey can be summarized as follows; A measurement of straight lines and the

horizontal angle from one point to another using Total Station.

The sides can be expressed as either polar coordinates (,d) or as rectangular coordinates (N, E).


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A traverse framework comprising of a series of connected lines where the lengths and directions are observed and measured.

The traverse framework can be OPEN or CLOSED traverse i.e., start at known point and ends at another known point or the same start point.


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Type of Traverses

Closed Traverse


A

H

G

F

ED

C

B

Control station

Traverse station

Closed traverse(polygon)

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Type of Traverses

Closed Traverse


A

H

G

F

ED

CB

Control station

Traverse station

Closed traverse(geometrically open)

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Type of Traverses

Open Traverse


Control station

Traverse station

AH

G

F

ED

CB

Open traverse

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Coordinates System

Points on the surface of the earth or on a plan can be accurately positioned by taking measurements to a known, stable point of reference.

Assume that the axes of the graph are referred to as North, South, East and West as shown in Figure.


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In above Figure, Point A is at (1,2) and Point B is at (9,5).

The referencing used that the x-axis is known as EASTINGS and the y-axis is known as NORTHINGS.


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There are two methods of referring the point;

Rectangular coordinates, or

Polar coordinates


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Rectangular Coordinates (Grid)

Rectangular coordinates are a system of locating points by means of the measurement of two perpendicular distances from the principal axes to that point. These two perpendicular distances are the easting and northing


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Rectangular Coordinates


Point A

Point B

North

EastEA

NA

(EA,NA)E=EB-EA

EB

NB

(EB,NB)

N=NB-NA

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Polar Coordinates

If R is the origin and P is the reference object, the point P can be located by its polar coordinates of angle and distance i.e. and D, where D is the distance from the origin and is a clockwise angle between R and P.


Northing

R

P

D

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Polar Coordinates


North

East

Point A

Point B

~ whole-circle bearingd ~ distance

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Coordinate Conversions


22

1

NEd

N

Etan

cosdN

sindE

Rectangular to polar Polar to rectangular

d

E

Nd

E

N

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Northing

There are three (3) reference directions (or datum meridian) that are used as traverse reference we should be associated with. They are:

Magnetic North,

Grid North, and

True North


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Meridian

A meridian (or line of longitude) is an imaginary arc on the Earths surface from the North Pole to the South Pole that connects all locations running along it with a given longitude.


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Meridian

The meridian that passes through Greenwich, England establishes the meaning of zero degrees of longitude, or the Prime Meridian


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Bearing Calculation

There are two types of bearing that are commonly used in geomatic engineering are:

Whole Circle Bearings (WCB), and

Quadrant Bearings (QB) or Reduced Bearing (RB).


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Whole Circle Bearing

The Whole Circle Bearing (WCB) of a line AB is defined as the clockwise angle from 0 to 360at A between the direction to North and the direction to B.

This is the standard way of defining a bearing in surveying

Bearing of AB = & BA =


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Whole Circle Bearing


bearing

bearing

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Quadrant Bearing

A quadrant bearing can be defined as the angle lying between 0 and 90, between the direction to the north or south and the direction of the line.

East and West directions are never used as reference lines.


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Quadrant Bearing


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WCB & QB


Bearing are measuredclockwise from NORTHand must lie in the range0

o 360

o

North0

o

East90

o

South180

o

West270

o

1st quadrant

2nd quadrant3rd quadrant

4th quadrant

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Angular Observation and Booking

Two most common methods in making angular observation in total station traversing are:

Internal angle method, and

Bearing method (commonly used in total station traversing)


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The Bearing Method

The procedure and bookings to be followed are as follows [Refer to Figure]: Instrument is set up at station B and station A is

sighted in face left. A known bearing i.e. 452020 is set on station A.

Station C is sighted and the reading is recorded.

The telescope is then transit to change to the face right.

With the face right setting, bearing to C and A are recorded.


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From To

Station Station Face Left Face Right Mean

A 000'00" 18000'00"

B 3026'30"

C 3026'20" 21026'40"

For improved precision the angle measurement can be repeated any number of times. The number of face left observations must be Equal the number of face right observations.

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LINEAR MEASUREMENT

The procedure of linear measurement is as follows:

Tripod with prism targets is set up at Station A and C.

Total station is set up on station B. Linear measurement or distance to BA and BC are taken and recorded.

Bearing to BA and BC are taken on face left and recorded.

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Classes of Traverses

o Generally, four classes;

o Standard traverse,

o Fist class traverse,

o Second class traverse, and

o Third class traverse

Why divided by four classes


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Classes of Traverses

o Main characteristics differ

o Precision,

o Bearing closure

o Measured distance,

o Observed bearing, and

o Definite bearing


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EXERCISE 1

Explain in detail how to set up a total station over a station mark.

Describe in detail the five permanent total station adjustments that should be tested from time to time.

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EXERCISE 2

The horizontal angles read at station A and station C are 733000 and 1452000 respectively. If the total station is set up at station B. What will be the internal angle ABC?

If the face left reading of the horizontal angle is 2252000, what is the most probable reading that you will obtain if the total station is transit and read in the face right?

The vertical angle reading of a total station is 10530 indicating that it is above the horizontal plane. What will be the true vertical angle?

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EXERCISE 3

What are the characteristics of a traverse?

Explain the significant difference between the methods of coordinate referencing in traverse?

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EXERCISE 4

Name the FOUR quadrant bearings by referring to the North and South directions.

The whole circle bearing (WCB) of a traverse line is 11530. What will be the value if it is described in quadrant bearing?

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Traverse Survey