Surveying I.

Surveying I.

Lecture 1.

Sz. Rózsa: Surveying I. – Lecture 1

Introduction

Historical Surveying

Surveying - Science and Profession

Methods of height determination

Levelling

The surveyors’ level

Outline


Introduction

Lecturers

:

Lectures

Dr. Szabolcs Rózsa

Department of Geodesy and Surveying,

K. building groundfloor 16.

Practicals

Dr. Lóránt Földváry

Department of Geodesy and Surveying,


Mr. Albert Kiss

Department of Geodesy and Surveying



Introduction

Course details

:

• First part of a two-semester-course

• 4 hours/week (equally divided between lectures and practicals)

Communication:

• Activities involve lectures, practicals, tutorials and a field practice

• Lectures - provide the theoretical background of the topics

• Practicals - practical sessions, in which You’ll carry out measurements and process them.

• Tutorials - if there’s a need for additional guidance in the preparation for assessments. Please note that You have to arrange an appointment in due time.

• Field practice - a 9-day-long intensive course after the course Surveying II.


Introduction

Attendance:

• Please attend all scheduled lectures, seminars and practicals

• Please note: attendance falling below 70% may lead to failing the course irrespective of the academic performance.


Introduction

Classroom tests:

• Altogether 4 classroom assessments:

• Practicals 1-4 (10 points)

• Using a theodolite – must pass

• Practicals 10-11 (10 points)

• Theory (involving the topics of the lectures) – 80 points

Course Evaluation:

Excellent good satisfactory pass fail

(5)

(4)

(3)

(2)

(1)

87-99

75-87

62-74

50-61

0-49

You’re required to achieve a minimum of 50% in each classrom test to pass the course.


Introduction

Learning resources:

• Some of the lecture notes are available for download on the website of the department: http://www.geod.bme.hu/index_e.html

• However You shall write own notes during the lectures, too.

• You’ll be suplied with computational sheets, field notes etc. during the course.

• Textbook:

A. Bannister - S. Raymond - R. Baker : Surveying (Seventh

Edition, Prentice Hall, 1998)

Cca. 16000 HUF


Lecture notes can be downloaded from:

Website http://www.geod.bme.hu/index_e.html


Website


Introduction




Levelling


Outline



What is Surveying?

The art of making measurements of the relative positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.

Since when?

The first surveying works date back to the antiquity, the

Greek provided the first account of surveying techniques.

Euclid founded the theoretical background for surveying by the development of his geometry.



Eratosthenes

(ca. 250 BC)

„Spherical Earth”




Introduction




Levelling


Outline



Surveying vs. Geodesy

• in most languages there are no distinctions between the terms

• in English (according to Vanicek - Krakiwsky):

• Surveying: the practice of positioning

• Geodesy: the theoretical foundation of surveying

Geodesy is the scientific background of Surveying as a profession.



Surveying:

The art of making measurements of the relative positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.

Geodesy:

Geodesy is the discipline that deals with the measurements and representation of the Earth, including its gravity field, in a three-dimensional time varying space.

Geodesy focus on the Earth and neglect any man-made features on it (e.g. buildings, public utilities, etc.), while surveying use the results of geodesy for positioning and mapping of these features.


Basic principles of Surveying

Recall the definition of Surveying:

The art of making measurements of the relative

positions of natural and man-made features on the Earth’s surface, and the presentation of this information either graphically or numerically.

How to achieve this?

Nowadays 3D positioning can be achieved using satellite techniques, too.

Let’s determine the position (X

P

, Y

P

) of point P!

Absolute vs Relative positioning

X

P

Y d

BP P d

AP

Y

P

B

(X

B

,Y

B

)

Control points

(known coords; marked on the field)

A

(X

A

,Y

A

) l

AB

X


Y

Basic principles of Surveying

Let’s determine the position of a third, unknown point (C).

We have two unknowns: X

P

, Y

P

We need two measurements: b a

• two distances

• one distance and an angle

• two angles

P d

BP d

AP d

AP b

B

(X

B

,Y

B

)

A

(X

A

,Y

A

) a a

X

According to the space involved:

Classification of Surveying

• relatively small areas

• surface of earth can supposed to be flat

• measurements plotted represent a horizontal projection of the actual field measurements

Note: The two radii can supposed to be parallel, when the l(A,B) is small.


Classification of Surveying

Don’t forget! Size does matter!

• large areas

• surface of the Earth can not supposed to be flat

• the curvature of the Earth is taken into account

Mostly used for establishing control networks, determining the size and shape of the Earth and determining the gravity field of the Earth.


How to create a countrywide coordinate system?

In order to use the relative positioning, a proper number of control points are needed. These points:

• are coordinated points;

• are marked.


Control Networks

Why is it necessary to have a common countrywide coordinate system?

Many engineering tasks cover a large area (highways, bridges, tunnels, channels, land registry, etc.), where the common coordinate system (reference system) should be available.

The Control Network provide us with control points given in the same refence system (coordinate system).

Thus measuring the relative positions of unknown points using these control points, the coordinates of the new points can be computed in the same reference system.


The role of Surveying in Civil Engineering Practice

Surveyors are needed:

• to maintain the geometric order during the construction process

• to provide fundamental data for the design and planning process

• to provide quantity control during the construction process (for example: earthwork quantities)

• to monitor the structure after the construction

Wrong geometry – the structure is not functional!

outstanding structures can be created!


The role of Surveying in Civil Engineering Practice

Surveying activities during the construction process

Before Construction

Planning and data collection

Observations in the field

Processing the observations

(office)

Drawing maps, plans or providing numerical data

Presenting documentation to the client

Under construction

Setting out on each phase of construction

Field checks of construction

Providing data and services to the client

After construction

Final (as-built) plan or map on the construction

Presenting documentation to the client

Deformation

Monitoring/

Load Tests


Outline

Introduction




Levelling




Question 1:

What does the height (elevation) of a point mean?

Question 2:

What does it mean, when point B is at a higher elevation than point A?

Answer 1:

The height of a point represents its energy level above a reference level.

Answer 2:

For example water flows from point B to point A.



Definition of height systems:

• The potential energy of a point should be represented by the height of a point. Hence water should flow from the higher elevation towards the lower elevation.

• Should have metric unit.

What should be the reference of height determination? What is the 0 level?

• Since the height systems should represent the potential energy level, we need a reference surface, which is an equipotential surface of Earth’s gravity field.

• The surface of calm water forms an equipotential surface

• Mean Sea Level – Kronstadt (Baltic Sea) is used in Hungary

(formerly Triest, Adriatic Sea).



Equipotential surfaces

A

H

A

H

B

B

MSL equipotential surface g

Gravity vector is always perpendicular to the equipotential surface.

Equipotential surface

Gravity vector

(=)

(=) horizontal surface vertical direction



1D position determination - determining the height

We can not determine absolute heights above the reference level

Relative height determination - determining the height differences

Levelling benchmarks are needed - control points for which the elevation is known.

B



H

BA



H

B



H

A

A

H

B

H

A

Reference level



How can we determine the height difference?

Two solutions:

• setting a horizontal plane, and measuring the offset from this plane

• measuring the slope and slope distance between the points

Levelling

Trigonometrical height determination

B l

AB



H

BA



H

B



H

A

A a

H

B

H

A

Reference level


Outline

Introduction




Levelling



The principle of levelling

Line of sight

(l

A

)



H

AB

A d

A l

A



H

AB

=l

A

-l

B

=(l

A

)d

A

-(l

B

)+ d

B

When d

A

= d

B

(spherical approximation, equal distance to A and B)



H

AB

=(l

A

)-(l

B

) d

B l

B

(l

B

)

B

Levelling

Over short distances the horizontal line and level line coincide.

For a distance of 100m the effect of the curvature is less than 1 mm.

The levelling device (called level) must be set up so, that the line of sight is perpendicular to the gravity vector (plumb line). -> the line of sight is horizontal.

Horizontal line of sight

Graduated staff Level

Graduated staff

Difference in height


Levelling


Introduction




Levelling


Outline


The Surveyor’s level

Tilting level

Diaphragm

Bubble tube

Tilting screw

Circular bubble Tilting axis

Levelling head

Clamping screw - to fix the telescope in one vertical plane

Tangent screw (slow motion screw) - to finely rotate the telescope along a vertical axis


Elements of Surveyor’s level

How to set the line of sight to be exactly horizontal?

More general: how to set anything to be exactly horizontal?

The bubble tube


The bubble tube

The radius determines the sensitivity of the bubble tube: a

R

1 a

R

2

R greater than R

1 2

Sensitivity: how much the bubble moves due to a given amount of inclination. The more the bubble moves, the more sensitive the bubble tube is.


The bubble tube

The determination of sensitivity: a

R

1 a

R

1

L l

1 a

L l

2 l

2

 l

1

L

 a

 radians

 a

 

 a

 radians





206264 .

8


Surveying I. – Lecture 1

Lecture 1.

Introduction

Historical Surveying

Surveying - Science and Profession

Methods of height determination

Levelling

The surveyors’ level

:

:

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