ARISTOTLE UNIVERSITY OF ThESSALONIKI
DEPARTMENT OF CIVIL ENGINEERING
DIVISION OF GEOTECHNICAL ENGINEERING
LABORATORY OF GEODESY

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The main research activities of the Laboratory of Geodesy are:

  Monitoring the deformation of technical works and ground landslides

  Control of geometrical quality of structures and industrial products

  Establishment and operation of a  Continuous Reference GPS station in Thessaloniki

  Applications of Global Positioning System in Geodesy, Geodynamics and Vehicle control and navigation

  Applications of Geographical Information Systems (GIS)

  The influence of the atmosphere on radio wave propagation

  Surveying monuments and archaeological sites

  Calibration of geodetic instruments

  Mapping the human body

  History of Geodesy and Cartography

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MONITORING THE DEFORMATION OF TECHNICAL WORKS AND GROUND LANDSLIDES
One of the major fields of research in the Laboratory of Geodesy is the measurement of the deformation of technical works and ground landslides. In this way, valuable information can be obtained helping the safe operation of every structure and the evaluation of construction theories and methods. Some examples of such activities are given below.
Use of a robotic geodetic system for 3D point positioning with measurement of polar coordinates
 

Leica robotic Total Station TCA2003 is used for deformation measurements and engineering surveying. It is a high-precision automatic measuring system enabling sets of target points to be re-measured automatically at predetermined intervals.
It uses automatic target-recognition system (ATR) for targeting. The whole procedure is controlled and organized through computer and software.

Monitoring the settlements of a 15,000 t liquid storage tank

The Laboratory of Geodesy is monitoring the settlements of a 15,000 t liquid chemical products storage tank founded on 112 long bored piles. The tank is located in the industrial zone at Western Thessaloniki. The observations started with the construction of the tank in 1983 and continue until today. 

Also, a similar structure (a 50,000 t sugar storage silo) at Platy, Emathia was under a surveillance program for a period of a year after its construction.

Research on the ground settlements observed in the area of Kalohori at the western part of Thessaloniki
Ground settlements have been observed for the last 35 years in Kalohori, a village and industrial area at the western part of Thessaloniki. These settlements have been continuously monitored by the Laboratory of Geodesy since 1992 with the help of a leveling network covering the area under investigation.

As it was found, the settlements have a 5 cm/year rate at the south-east part of the area and can be attributed to the intense water pumping through tenths of state and private boreholes in the area. 

The picture at the left shows the observed settlements (in cm) for a period of three years (1996-1998).

 

Determination of horizontal displacements during the excavation of two drainage pump stations in Thessaloniki

 

In this project, continuous monitoring of the stability of the peripheral wall of two drainage pump stations was done with geodetic methods to control the behavior of the construction during excavation works due to safety reasons.

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CONTROL OF THE GEOMETRICAL QUALITY OF STRUCTURES AND INDUSTRIAL PRODUCTS
Positioning systems based on the measurement of 3D intersections 

The Laboratory of Geodesy is using two 3D positioning systems  for metrology applications. 

One system consists of 4 Nikon Total Stations and is used for digitizing existing buildings and structures.

The other system consists of 4 high accuracy Leica electronic theodolites and is used in Industrial Metrology applications. With this system it is possible to derive 3D coordinates of points on small and large objects (industrial products) up to an accuracy of 1/100mm.


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CONTINUOUS REFERENCE GPS STATION IN THESSALONIKI

 The Laboratory of Geodesy established a Continuous Reference GPS Station in Thessaloniki, named THES. This is the only continuous operating GPS station in Northern Greece.

THES station consists of an Ashtech Z-12 GPS receiver with its antenna placed on top of the building where the Laboratory is housed. The GPS station functions in two different ways:

A: It transmits differential RTCM corrections in real time for high precision positioning (Real Time Kinematic DGPS, RTK-DGPS) through a UHF radio network. The corrections are available to anyone operating a  RTCM-ready rover GPS receiver in the same radio frequency. In this way, its possible to perform real time surveying measurements, setting out works and vehicle or vessel navigation.

B: The GPS receiver records raw data on a 24 hour basis. The measurements are stored in the computer of the system and are available to surveyors or other users working with GPS in the area of Thessaloniki. Then, they can use the THES data in combination with their GPS measurements for post-processing positioning computations

 

   

The antennas of the GPS station and the UHF radio network

 

In short time the GPS raw data will be available through the web-server of the Laboratory of Geodesy 


  PowerPoint presentations:

Thessaloniki Continuous Reference GPS Station: Initial Estimation of Position, Proceedings of EGS XXV General Assembly, Nice, France, 2000 (P. Savvaidis, I. Ifadis, K. Lakakis).


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APPLICATIONS OF GPS IN GEODESY

The application of GPS techniques in Geodesy include:

Establishment and measurement of trigonometric control networks.

Surveying with GPS receivers. 

Re-measurement of the control network of the City of Thessaloniki with GPS techniques.
In 1994-1995 a re-measurement of the control network of the City of Thessaloniki with GPS techniques was performed in collaboration with the Division of Geodesy and Surveying, Department of Rural and Surveying Engineering, A.U.Th. (Prof. K. Katsambalos) and the Department of Surveying Works of the Municipality of Thessaloniki (I. Mavromatis). 

The control network consisted of about 100 stations and was measured with four GPS receivers. The project also included the adjustment of the network and the computation of new sets of coordinates.

Road geometrical characteristics verification with GPS techniques

   

The Laboratory of Geodesy has developed a  road geometrical characteristics verification  3D system with the employment of 4 or 5 L1/L2 GPS receivers carried on a vehicle with the help of a two-level rectangular metal frame.

GPS measurement of the height of peeks of Mountain Olympus
In September 1996, the Laboratory of Geodesy with the help of the Thessaloniki Mountaineering Club used GPS techniques for the re-measurement of the height of several peeks of Mountain Olympus, the Mountain of Gods according to Greek mythology.

As it came from the measurements and computations, the absolute height of Mitikas and Stefani was found equal to 2918.8 ± 0.1 m and 2912.3 ±  0.1 m instead of the existing values of 2917 m and  2909 m respectively.

(With the collaboration of Prof. K. Katsambalos, Department of Rural and Surveying Engineering, A.U.Th.)

Mitikas - Mt. Olympus, 1996


  PowerPoint presentations:

Modelling a Vehicle - GPS System for Road Geometrical Characteristics Verification: A First Approach. Proceedings of IAIN 25th Anniversary World Congress, San Diego, 2000 (P. Savvaidis, I. Ifadis, K. Lakakis).

Applications of the GPS system in the Laboratory of Geodesy. Seminar "Laboratory of Geodesy - Research activities and related services", Thessaloniki, 1999 (P. Savvaidis).


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APPLICATIONS OF GPS IN GEODYNAMICS
Control network measurements in the seismic area of Volvi, Mygdonia near Thessaloniki

 In 1978, severe earthquakes damaged an extensive area of Northern Greece including the city of Thessaloniki. The main shocks came from the seismic zone of Volvi, NE of Thessaloniki. A 16 station geodetic control network was established in 1979 using classical techniques. In 1994 and 1997 the control network was extended and re-measured with GPS receivers by the Laboratory of Geodesy in collaboration with the Laboratoire de Geophysique Interne et Tectonophysique, University Joseph Fourier, Grenoble and the Division of Geodesy and Surveying, Department of Rural and Surveying Engineering, A.U.Th. (Prof. K. Katsambalos) [EU project ENVIRONMENT "EURO-SEISTEST, Volvi - Thessaloniki, a European Test Site for Engineering Seismology, Earthquake Engineering and Seismology".

The extended geodetic control network in the area of Mygdonia, 1997

Control network measurements in the seismic area of the Corinthian Bay

 

Members of the staff of the Laboratory of Geodesy participated in the GPS measurement of a 30 station control network at the seismic area of the Corinthian Bay. The measurements were carried out by the Departement se Sismologie, Institut de Physique du Globe de Paris, members of the staff of the Division of Geodesy and Surveying, Department of Rural and Surveying Engineering, A.U.Th. and the National Technical University of Athens (EU program "High Quality Earthquake Strong Motion Measurements for Structural and Seismic Source Studies", 1993).


  PowerPoint presentations:

Employment of a Permanent Monitoring GPS Network at the Seismic Area of Volvi, Greece. Proceedings of IAIN 25th Anniversary World Congress, San Diego, 2000 (P. Savvaidis, I. Ifadis).


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APPLICATIONS OF GPS IN VEHICLE CONTROL AND NAVIGATION - THE VECON (VEhicle COntrol and Navigation) SYSTEM 

The Automatic Vehicle Location (AVL) systems utilizing the Global Positioning System are very effective for monitoring the movement of vehicles. The accuracy of such systems can be of the order of 15-20 m, when using an autonomous GPS receiver (SA off) or of the order of 0.10-3 m, when using differential GPS in real time or with post processing.

The combined use of AVL and GIS systems give significant capabilities for the management of fleets of vehicles, especially that of Emergency Response authorities (police, fire department, ambulances).  From such systems, also public and commercial transportation fleets can benefit in their organizational aspects.

In all cases, better services can be provided to the public.  

Real Time Differential GPS positioning

In order to achieve better accuracy in the positioning of moving vehicles, Real Time Differential GPS (RT-DGPS) techniques can be used.

 

In a RT-DGPS system at least two GPS receivers must be used. One of them is operating as the Base Station at a known point and the other as a Rover receiver placed on a vehicle. The Base Station computes its position from the GPS measurements (with the expected error) and compares it with its known coordinates. From this comparison the differences are computed and transmitted as differential corrections in a specific format through a radio network. 

The Rover receiver computes its position from the GPS measurements (with the expected error)  and corrects it in real time with the received differential corrections. So, the Rover receiver computes more accurate coordinates (geographical or Cartesian). This set of coordinates can also be transmitted in a specific format (NMEA) through the radio network to a Control Station.

The VECON (VEhicle COntrol and Navigation) System

 

The VECON (VEhicle COntrol and Navigation) System consists of two major sub-systems:

 

The Control Station

 

The Vehicle Units

 

The Control Station of the VECON System  

The Control Station of the VECON System

CONTROL STATION

Continuous Reference GPS Station for transmission of RTCM corrections. 

Radio modem for the communication among the Control Station and Vehicle Units.

Computer facilities and software for monitoring the movement of the Vehicle Units in GIS environment with the digital map of Greater Thessaloniki.

Conventional Transceiver (UHF 400-470 MHz) with its antenna for NMEA positioning messages input.

Transmitter for RTCM corrections (UHF 400-470 MHz) with its antenna.  

The Vehicle Units of the VECON System 

VEHICLE UNIT

GPS antenna. 

GPS receiver with modem to receive RTCM corrections and transmit NMEA positions to the Control Station of the system. 

Conventional Transceiver (UHF 400-470 MHz) with its antenna.  

Vehicle unit equipment

 VECON  System capabilities

A major problem in the use of Fleet management systems in an urban area is the lack of accurate digital maps. Also, the GIS software platform used for providing network analysis capabilities needs traffic data which are not always available or up-to-date. VECON system is operating based on the concept of using a number of public vehicles as sensors for mapping the road network and monitoring the traffic conditions in an urban area. Through the continuous use of the system and DGPS operation, an accurate digital map of the street network of the area can be generated and primary traffic data, like transit times, can be collected on a permanent base by using GPS as an accurate timer with spatial reference.  In this way, the digital map is gradually created with the same accuracy as the future positioning of vehicles and standard traffic characteristics as traffic volume, traffic density, traffic capacity, etc. can be obtained and updated. 

The VECON system can be also used for real time monitoring of traffic conditions under disaster or emergency situations where all the previously available data become invalid or unreliable.

The VECON  System described here has the following capabilities:

It functions as a self-governed closed system because it can produce the necessary digital cartographic database from its incoming information.

It records travel times with the help of the GPS system for every road segment driven through by each Vehicle Unit, thus providing a digital time database from which traffic parameters can be also computed.

It can make use of existing vehicle fleets in an urban area, rapidly collecting data and covering the whole road network in the simplest way. 

It can be defined as a dynamic system because, during the everyday operation, it continuously updates and corrects its databases, optimizing in this way their effectiveness. 

It can be used for real time monitoring of traffic conditions under disaster or emergency situations, when all previously available data become invalid or unreliable.


  PowerPoint presentations:

Adaptive Filtering Method for Building a Time Urban Traffic Network by Using Kinematic DGPS Observations in Everyday Traffic Conditions, 3rd Inter. Symp. on Mobile Mapping Technology, Cairo, 2001 (P. Savvaidis, I. Ifadis, K. Lakakis).

Use of a Fleet Management System for Monitoring Traffic Conditions After a Major Earthquake in an Urban Area, Proceedings of 22nd Urban and Regional Data Management Symposium, Delft, 2000 (P. Savvaidis, I. Ifadis, K. Lakakis).

Everyday Mapping of Traffic Conditions – An Urban Planning Tool. Proceedings of Inter. Symp. “Application of Geodetic and Information Technologies in the Physical Planning of Territories”, Sofia, 2000    (P. Savvaidis, I. Ifadis, K. Lakakis).

VECON (Geotracim): A geo-informatics real-time system for the simulation of urban traffic conditions. 13th National Symposium on Transportation and Technologies, Athens, 2000 (K. Lakakis, P. Savvaidis, A. Kokkalis).

Development of a vehicle navigation system for the improvement of response time in case of emergencies. Meeting on Seismic Hazards Confrontation, Thessaloniki, 1999 (P. Savvaidis, K. Lakakis).


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APPLICATIONS OF GEOGRAPHICAL INFORMATION SYSTEMS (GIS)
The Laboratory of Geodesy is activated in the customization of Geographical Information Systems (GIS) for various applications. In the software library of the Laboratory there are GIS program licenses of ESRI ArcInfo and ArcView as well as Autodesk AutoMap. 
 

 

An Environmental Information System for the Area of Thessaloniki, Greece

 

The cadastral GIS System of the University of Thessaloniki


  PowerPoint presentations:

Building a GIS: A Cadastral Project as the Base for a Growing Powerful Information System, Proceedings of Inter. Symp. “Application of Geodetic and Information Technologies in the Physical Planning of Territories”, Sofia, 2000 (I. Ifadis, P. Savvaidis).

Development of an Environmental Information System for the Area of Thessaloniki, Greece, Proceedings of Inter. Symp. "Application of geodetic and information technologies in the physical planning of territories", Sofia, 2000 (P. Savvaidis, I. Ifadis).


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INFLUENCE OF THE ATMOSPHERE ON RADIO WAVE PROPAGATION

The influence of the atmosphere on radio wave propagation, mainly for earth-to-space links is another main research aspect in the Laboratory of Geodesy. The research area includes study of the atmospheric refraction angle and delay under various atmospheric conditions and for various areas of the earth. According to this approach different estimation models for the atmospheric refraction and delay have been developed, tested, and proposed. 

Analysis of the atmospheric delay based on the characteristics of the atmosphere and the trajectory of the radio wave.

Typical Atmospheric wet, hydrostatic and total delay diagram for the Thessaloniki area. (Macedonia Airport, 1-5-1991, Temperature 291.36 Kelvin, Rel. Humidity 64%, Atmospheric Pressure 1013 mbar)

 The atmospheric delay can be separated in wet and hydrostatic or dry. The wet part of the delay is due to the atmospheric humidity, while the hydrostatic or dry is basically affected by the dry part of the atmosphere (the definition of dry or hydrostatic depends on the definition of the radio refractivity equation).

The study of the atmospheric delay is based on vertical atmospheric profiles given usually in the form of radiosonde data. Radiosonde data are usually available on a daily basis from various stations all around the world and in most cases are published in the web (North American RAOB database, The British Atmospheric Data Centre, Radiosonde Connections). 

Estimation of the atmospheric delay
 

For the estimation of the atmospheric delay, wet and dry or hydrostatic several models have been developed. Some of them use surface atmospheric parameters for the delay estimation while other are based only on the station geographic parameters and the day of the year. In the adjacent figures the hydrostatic delay estimation error is given against the latitude of the stations used.

The influence of the horizontal variations of the atmosphere on the delay estimation.

The atmospheric delay is not a static phenomenon affected only from the vertical distribution of the meteorological/atmospheric parameters, but is affected also from the horizontal variations of the atmosphere. This influence is not included in most of the models used to estimate the delay. This introduces a certain error in the delay estimation. This error has to be studied analytically and be well understood. In general it was found that there is a North-South component that affects the delay, while in other cases this distribution might be affected from local meteorology and geography.  In the picture to the left the distribution of total mean delay in the area of the Mediterranean is shown.

  PowerPoint presentations: 

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SURVEYING OF MONUMENTS AND ARCHAEOLOGICAL SITES

Another main field of activity of the Laboratory of Geodesy is surveying of Monuments and archaeological sites with geodetic methods. The Laboratory is involved in surveying of Byzantine churches and buildings of historical interest in the area of Thessaloniki and other places in Northern and Central Greece. In these projects, modern instrumentation such as reflectorless EDM instruments and Total Stations is used.

 

Surveying the Acropolis of the pre-historic site at Sesclo, Magnisia

 

Surveying an old building (Casa Bianca) in Eastern Thessaloniki


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CALIBRATION OF GEODETIC INSTRUMENTS

The Laboratory of Geodesy uses a  HP Laser Interferometer (accuracy of distance difference measurement 10-7 m) for the control and calibration of distance measurement instruments (tapes, EDM instruments, Total Stations), theodolites etc.

Also, there is a modern 4-axis autocollimator for the control and adjustment of the telescope axis and the reticule of geodetic (optical and electronic) instruments. The Laboratory can adjust and repair optical instruments. 

EDM instruments and Total Stations are calibrated for zero and cyclic errors in the Laboratory's baseline (8 pillars, length 910 m) located in the area of "Macedonia" Airport of Thessaloniki. 

 

HP Laser Interferometer

The autocollimator

The calibration baseline in the area of Thessaloniki Airport


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MAPPING THE HUMAN BODY 
Computed Tomography (CT ) or Computerized Axial Tomography (CAT) is a quick and reliable method for surveying the internal organs of the human body. An x-ray tube circles the patient taking multiple x-rays. A computer combines the x-ray images into cross-sectional pictures, or "slices" of the body. The absorption characteristics of the radiated tissues, effects the intensity of the x-ray beam which produces images showing internal structures such as blood clots, skull fractures, tumors and infections. The data can be further manipulated and digitized in the geodetic way to reconstruct 3-D images of the internal of the body, thus helping diagnostic procedures and surgical  operations.
 

Mapping (digitizing) the human brain

Computed Tomography of the human brain


  PowerPoint presentations:

Application of cartography to the Medical Science: Surveying the human body. 6th National Cartographic Symposium, Athens, 2000 (P. Savvaidis, G. Badellas).


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HISTORY OF GEODESY AND CARTOGRAPHY


    From Heron to geodetic satellites 

                 The historical development of surveying instruments 

 


             Maps on stamps 


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