Geodetic Control Network
Lecture 1.
The purpose of Geodetic Control Networks,
their application and the history of their establishment.
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
Introduction
Lecturers:
Lectures
Dr. Szabolcs Rózsa
Department of Geodesy and Surveying,
K. building groundfloor 16.
Practicals
Dr. Szabolcs Rózsa
Department of Geodesy and Surveying,
K. building groundfloor 16.
Introduction
Course details:
• one-semester course
• 3 hours/week (2 lectures + 1 practical)
• practicals will be held on every second week of
the semester
• the course is a foundation course for the Geodetic
Control Networks Field Practice (6 days)
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.
Practicals:
• Precise levelling (electronic and and tilting level);
• Computations on the ellipsoid;
• Computation of links to high points;
• Fast-static GPS observations and their processing.
Introduction
Classroom tests:
• Altogether 3 classroom assessments:
• Computation of observations in a tower – 20
points
• Horizontal Control Networks – 40 points
• Vertical and Gravimetric Control Networks –
40 points
• 2 homeworks, which must be finished correctly
Course Evaluation:
Excellent
good
satisfactory
pass
fail
(5)
(4)
(3)
(2)
(1)
87-99
75-87
62-74
50-61
0-49
Introduction
Learning resources:
• Lecture notes as ppt files on the webpage.
http://www.geod.bme.hu/index_e.html
• However You shall write own notes during the
lectures, too.
• You’ll be supplied with computational sheets,
field notes etc. during the course.
• Textbook:
Torge, W.: Geodesy (Third Edition, de Gruyter)
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
Surveying - Science and 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 manmade features on it (e.g. buildings, public utilities,
etc.), while surveying use the results of geodesy for
positioning and mapping of these features.
Classification of Surveying
According to the space involved:
B
A
Plane Surveying
• relatively small areas
B
• 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, if the
l(A,B) is small.
l

A
l cos 
R
R
Classification of Surveying
Geodetic Surveying
B
l
• large areas
• surface of earth can not
supposed to be flat

A
l cos 
• the curvature of the Earth
is taken into account
Mostly used for
• establishing control
networks,
• determining the size and
shape of the Earth
• determining the gravity
field of the Earth
R
R
Planar approximation
Spherical approximation
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
Geodetic Control Networks
• Surveying and Geodesy relies on a set of
permanently marked points, which is called the
Geodetic Control Network.
• The positions (co-ordinates) of these points are
detemined using geodetic and gravimetric
observations in an appropriate frame.
• Geodesy relies on triangulations, trilaterations,
levellings, satellite geodetic observations and
gravimetric observations
• The networks belong to the national/international
infrastructure and serve as a basis for not only
surveying, but geoinformation services, land registry
and many other location based service.
Control points - benchmarks
Control Networks
A set of control points covering a large region.
Please recall: The control points are
necessary for the definition of a
coordinate system.
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
The coordinate systems of GCN
• Geocentric coordinate system (satellite geodesy)
• Surface coordinate systems (based on the geoid ->
ellipsoid)
Surface coordinate systems
• 3D = 2D + 1D
• 2D is the coordinates on the surface (e.g. latitude,
longitude) – horizontal coordinates
• 1D is the distance between the point and the
reference surface (e.g. ellipsoidal height) – vertical
coordinates
• The physical point is projected to a reference
surface (Helmert or Pizetti – see it in the course on
Geodesy)
The coordinate systems of GCN
The vertical coordinates
The height system should have a physical meaning, it
should be linked to the potential of the point.
In reality the height above the sea level is used as a
vertical coordinate.
Since the vertical coordinates have a different
reference surface, and the observation techniques are
significantly different:
Traditionally the geographic distribution of
the points of the horizontal control networks
and the vertical control networks are
different.
Control Networks
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.
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
Static vs Dynamic Networks
Static view (up to the early 20th Century)
The Earth is a rigid body, the coordinates and the
gravity field do not change.
The contradictions between remeasured GCNs were
explained by the higher errors of previous
observations.
Dynamic view
The Earth is not rigid, plate tectonics exist, therefore
the control points may change their coordinates.
Repeated observation and computation of the
networks enable us to split the coordinate error in
two parts:
• determined by the deformation of crust;
• caused by observation error.
Dynamic Networks
In order to assess the deformations of the crust:
• the location of points should be chosen using the
results of other disciplines (geophysics, geology, etc.);
• the points should be marked in a suitable manner;
• displacement rates of approx. 1mm/yr should be
exceeded.
New Geodetic Control Networks should be
planned and established so, that it provides a
basis for surveying and geodesy as well as
enables the determination of recent crust
deformations.
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
The extent of geodetic control networks
Basically the extent is defined by national borders.
But:
• National Geodetic Control Networks are connected
to neighbouring countries;
• continental networks are established, and
• world wide networks are established.
This course deals with the national geodetic
control networks basically.
The hierarchy of geodetic control networks
Geodetic Controll Networks are established in many steps.
The sequence of steps defines the order of the geodetic
control network.
The number of orders depends on:
• the size of the area;
• the type of the network.
In Hungary:
Horizontal networks: 1st-5th order (1-3: high-order
control network; 4-5: low-order control network.)
Vertical and Gravimetric: 1st – 3rd order networks.
The establishment and maintenance of GCN
The establishment and maintenance of Geodetic Control
Networks are of national interest.
In Hungary: The horizontal geodetic control networks up to
the 4th order and the vertical and gravimetric networks up to
the 3rd order are established and maintained on a national
basis. Thus these networks are called: National Geodetic
Control Networks (NGCN).
What about the 5th order horizontal control points?
They are established on a „customer need” basis and they
are not maintained on the national level.
Outline
Introduction
Surveying vs. Geodesy
Geodetic Control Networks
The coordinate systems of GCNs
Static vs Dynamic Networks
The hierarchy and establishment of
GCNs
The roles of the 1st order network
The roles of the 1st order networks
The 1st order network:
• provides a consistent frame for the detail surveys;
• represents the country internationally (participate in
regional, continental or world-wide geodetic control networks)
to provide a constistent coordinate frame in a larger region;
• must enable repeated observations on the points to:
• monitor the deformation of Earth’s crust;
• to assess the accuracy of previous geodetic control
networks.
• helps to determine the theoretical shape of the Earth (the
geoid);
• provides a basis for establishing the network of collocated
points, where repeated observations of various geodetic
techniques can be made (GNSS, gravimetry, levelling, etc.) to
establish a European scale vertical control network for
geokinematic applications.
Thank You for Your Attention!