Γιώργος Πανταζής - Academia.edu (original) (raw)

Papers by Γιώργος Πανταζής

Journal of Civil Engineering and Architecture, Jul 28, 2011

In order to monitor the deformations of modern constructions a local 3D network was usually being... more In order to monitor the deformations of modern constructions a local 3D network was usually being established at the surrounding area. The centering error, of both the instrument and targets, causes significant uncertainties in the determination of the x, y, z coordinates of the network's points. In order to assure precise centering for both the instrument and targets, not only for the accessible but also for the inaccessible network's points, a prototype way of marking is being implied. A special semi-permanent portable metallic stand (photo 1) was manufactured for marking the accessible points. The stand provides forced instrument centering of the order of ±0.1mm. It is light enough to carry, it accelerates and facilitates the centering and leveling of the instrument as well as it eliminates the time needed for the measurements. The applied laboratory checks in order to certify the suitability of its use and the provided accuracy are being described. For the inaccessible points special targets were used. The targets were put in permanent attachments (photo 7), (photo 8), which were also manufactured. Useful conclusions were drawn when these special accessories were used in to a 3D network, which was established for the monitoring of a new football stadium. Two measurement phases were carried out. The first one with the stadium being empty and the second one when it was crowded (about 32000 people) during a significant football match.

SUMMARY GNSS measurements are widely used for the monitoring of several structures’ deformations ... more SUMMARY GNSS measurements are widely used for the monitoring of several structures’ deformations such as dams, bridges, high-rise buildings as well as landslides and earth crustal movements. In most cases the use of GNSS receivers is more convenient as it ensures continuous measurements and provides unmanned observations, long or short baselines measurement without visibility between the points. Moreover the accuracy of the static relative positioning reaches the sub-cm level. According to the usual procedure both horizontal and vertical change vectors of each point’s position are calculated in order to examine whether they should be considered as displacements or they are within the noise of the measurements. As many commercial GNSS software packages don’t provide the full variance – covariance (VCV) matrix as an output, there is often a miscalculation of the absolute and relative error ellipses or ellipsoids for any confidence level. Moreover the baselines’ solution usually provid...

This paper presents the integrate procedure for the documentation and fabrication of the 3D Digit... more This paper presents the integrate procedure for the documentation
and fabrication of the 3D Digital Terrestrial Model (DTM) of
inaccessible and rough surfaces. The proposed procedure combines
the use of modern Image Assisted Total Stations (IATS) with Rapid
Prototyping (RP) Technology. The determination of the measurement
accuracy, as well as, the a-priori estimation of σo of the surface
creation is achieved by using the Monte Carlo technique and the
least square method. Also, basic concepts and principles of RP
technologies are presented. The application of the procedure was
realized at the difficult and inhospitable area of the central crater
“Stefanos” on Nisyros Island’s Volcano, Greece. The a-priori
calculation of the minimum essential scanning step, as well as, the
testing use of two IATSs is included. Additionally, the elaboration and
the special algorithms used for the actual RP fabrication of the
crater’s tangible model are illustrated. Finally a scholastic check of
the model’s reliability is applied.

In order to monitor the deformations of modern cons tructions a local 3D network was usually bein... more In order to monitor the deformations of modern cons tructions a local 3D network was usually being established at the surrounding ar ea. The centering error, of both the instrument and targets, causes significant uncertai nties in the determination of the x, y, z coordinates of the network's points. In order to assure precise centering for both the i nstrument and targets, not only for the accessible but also for the inaccessible network's points, a p rototype way of marking is being implied. A special semi-permanent portable metallic stand (p hoto 1) was manufactured for marking the accessible points. The stand provides forced instru ment centering of the order of ±0.1mm. It is light enough to carry, it accelerates and facilitat es the centering and leveling of the instrument as well as it eliminates the time needed for the me asurements. The applied laboratory checks in order to certify t he suitability of its use and the provided accuracy are being described. For the in...

GNSS measurements are widely used for the monitoring of several structures’ deformations such as ... more GNSS measurements are widely used for the monitoring of several structures’ deformations
such as dams, bridges, high-rise buildings as well as landslides and earth crustal movements.
In most cases the use of GNSS receivers is more convenient as it ensures continuous
measurements and provides unmanned observations, long or short baselines measurement
without visibility between the points. Moreover the accuracy of the static relative positioning
reaches the sub-cm level.
According to the usual procedure both horizontal and vertical change vectors of each point’s
position are calculated in order to examine whether they should be considered as
displacements or they are within the noise of the measurements.
As many commercial GNSS software packages don’t provide the full variance – covariance
(VCV) matrix as an output, there is often a miscalculation of the absolute and relative error
ellipses or ellipsoids for any confidence level. Moreover the baselines’ solution usually
provides unrealistically optimistic standard errors. Thus it is often ignored or empirically
scaled. The right weight estimation is needed in order to produce an objective VCV matrix
from the network adjustment.
This work presents a complete, reliable processing methodology for 3d monitoring by using
GNSS measurements. This processing methodology allows the use of the initial baselines
measurements and leads to analytical results according to the least squares method and the
law of propagation of errors.
Also the paper uses a specific technique for the preferred definition of the weights in order to
be used for the unequal weight adjustment.
The network adjustment is carried out in the geocentric reference system by using linear
equations and the indirect observations method. The full objective VCV matrix of the network
is provided. The appropriate full rotation matrices are used in order to transform the
displacement vectors as well as their variances and covariances in a local oriented plane
projection in order to be more perceptible and useful.
Finally, the limitations of the proposed procedure are represented by the calculation of the
difference to the error ellipses when the full VCV matrix is used.

Geodesy can make a significant contribution to the monitoring of structures. The geodetic methods... more Geodesy can make a significant contribution to the monitoring of structures. The geodetic methods that have been
developed can give reliable results. The aim of this article is to use the results obtained through the monitoring of
a structure to predict its position in the future, using ANNs. It presents a detailed study on the development of an
ANN that can be used to predict vertical displacements in a cultural heritage monument, with the ultimate aim of
preventing it from falling apart. To this end, a geodetic network of 15 control points was established. The results
of twelve series of geodetic measurements and adjustments to this network are used in this study. Using the
trained ANN, the vertical displacement (ΔΗ) of any specific point in the monument’s geodetic network can be
predicted for a certain time in the future, with an uncertainty of ±0.5mm.

Apollo’s sacred island, Delos, is an extended archaeological site, which contains important monum... more Apollo’s sacred island, Delos, is an extended archaeological site, which contains important
monuments dating from prehistoric to Hellenistic times. In this article the orientation
of some of the most significant monuments of the site are studied.
Each monument has been measured by means of modern accurate geodetic and astrogeodetic
methods and instrumentation so that its plan, its main (longitudinal) axis,
the profile of the perceptible horizon as seen from the monument and the astronomical
azimuth of the main axis are determined.
Special attention and study have been reserved to the Cave of Kynthos (Andron), as
the latter was considered as an ancient observatory.
This study attempts also a possible dating of the measured monuments based on
their orientation and its relation to special celestial bodies.
All data deduced by measurements and calculations, as well as historical information
have been used for the creation of a database in Macromedia software.

As many studies worldwide [25], [6], [9], [17] have proven, there is a significant r... more As many studies worldwide [25], [6], [9], [17] have proven, there is a
significant reason for the study of a monument. This is the actual orientation that the
founders gave to the monument during its foundation. The orientation of a monument,
especially a religious one, follows some strict rules according to each religion,
tradition and belief. Today, the orientation of a monument may be determined and
registered accurately and easily thanks to advanced technology. Especially if
astrogeodetic measurement methods are being used then the orientation may be
detected with adequate accuracy. This gives future generation’s reliable information
which can facilitate for a better understanding on the purpose behind the erecting of
each monument. This paper presents the results of two research programs, which
focused on this subject. In order to disseminate the results of these two projects
worldwide, the information, is organized in database. Two different software were
used, Macromedia and ArcGIS. The ease of use and the various options of usage will
be discussed as will the final results.

The exact date of the foundation of the Katholikon of Daphni monastery is unknown. Based on the s... more The exact date of the foundation of the Katholikon of Daphni monastery is unknown. Based on
the stylistic data of its mosaic decoration the archaeologists suggest that its mosaics date to the end
of the eleventh century, which is either a terminus ante quem for the construction of the Katholikon
or the mosaic decoration is contemporary to this construction.
In this paper we attempt to determine the foundation date of the Katholikon of Daphni, on the
base of its astronomical orientation and by applying the general astrogeodetic method elaborated by
one of us (G. Pantazis) in this case. As results from our investigation, the Katholikon, which is
sacred to the Virgin Mary, was very likely founded on the day of the celebration of the Dormition
of the Virgin in 1153, i.e. in August 15, 1153 (±8years). If it is so, both the church and its famous
mosaic decoration date circa half a century later than it is generally accepted by the archaeologists.

This paper presents the integrate procedure for the documentation and fabrication of the 3D Digit... more This paper presents the integrate procedure for the documentation and fabrication of the 3D Digital Terrestrial Model (DTM) of inaccessible and rough surfaces. The proposed procedure combines the use of modern Image Assisted Total Stations (IATS) with Rapid Prototyping (RP) Technology. The determination of the measurement accuracy, as well as, the a-priori estimation of σo of the surface creation is achieved by using the Monte Carlo technique and the least square method. Also, basic concepts and principles of RP technologies are presented. The application of the procedure was realized at the difficult and inhospitable area of the central crater “Stefanos” on Nisyros Island’s Volcano, Greece. The a-priori calculation of the minimum essential scanning step, as well as, the testing use of two IATSs is included. Additionally, the elaboration and
the special algorithms used for the actual RP fabrication of the crater’s tangible model are illustrated. Finally a scholastic check of the model’s reliability is applied.

The planned astronomical orientation and positioning of all kinds of monuments was proved by nume... more The planned astronomical orientation and positioning of all kinds of monuments was proved by numerous investigations all over the world since the 19th century. Some cult, social or utilitarian purposes dictate a concrete orientation for each one. In this paper are being determined the individual orientation and the dating of Parthenon and He-phaisteion as well as a strong relationship between these significant monuments of the classical era is emerged. The exceptional symmetric placing of these monuments, as proved by this research, in ancient Athens is truly remarkable. Thus the strong religious relationship between the temples is also geometrically documented. The modern instru-mentation used today and the special developed astrogeodetic methodology permit the accurate (some arc seconds) determination of a monument’s orientation. Additionally this fact may be also a long discussion between archaeologists, archaeoastronomers and humanists.

Volume 14 - Issue 2 by Γιώργος Πανταζής

The planned astronomical orientation and positioning of all kinds of monuments was proved by nume... more The planned astronomical orientation and positioning of all kinds of monuments was proved by numerous investigations all over the world since the 19 th century. Some cult, social or utilitarian purposes dictate a concrete orientation for each one. In this paper are being determined the individual orientation and the dating of Parthenon and He-phaisteion as well as a strong relationship between these significant monuments of the classical era is emerged. The exceptional symmetric placing of these monuments, as proved by this research, in ancient Athens is truly remarkable. Thus the strong religious relationship between the temples is also geometrically documented. The modern instru-mentation used today and the special developed astrogeodetic methodology permit the accurate (some arc seconds) determination of a monument's orientation. Additionally this fact may be also a long discussion between archaeologists, archaeoastronomers and humanists.

Journal of Civil Engineering and Architecture, Jul 28, 2011

This paper presents the integrate procedure for the documentation and fabrication of the 3D Digit... more This paper presents the integrate procedure for the documentation and fabrication of the 3D Digital Terrestrial Model (DTM) of inaccessible and rough surfaces. The proposed procedure combines the use of modern Image Assisted Total Stations (IATS) with Rapid Prototyping (RP) Technology. The determination of the measurement accuracy, as well as, the a-priori estimation of σo of the surface creation is achieved by using the Monte Carlo technique and the least square method. Also, basic concepts and principles of RP technologies are presented. The application of the procedure was realized at the difficult and inhospitable area of the central crater “Stefanos” on Nisyros Island’s Volcano, Greece. The a-priori calculation of the minimum essential scanning step, as well as, the testing use of two IATSs is included. Additionally, the elaboration and
the special algorithms used for the actual RP fabrication of the crater’s tangible model are illustrated. Finally a scholastic check of the model’s reliability is applied.

The planned astronomical orientation and positioning of all kinds of monuments was proved by nume... more The planned astronomical orientation and positioning of all kinds of monuments was proved by numerous investigations all over the world since the 19 th century. Some cult, social or utilitarian purposes dictate a concrete orientation for each one. In this paper are being determined the individual orientation and the dating of Parthenon and He-phaisteion as well as a strong relationship between these significant monuments of the classical era is emerged. The exceptional symmetric placing of these monuments, as proved by this research, in ancient Athens is truly remarkable. Thus the strong religious relationship between the temples is also geometrically documented. The modern instru-mentation used today and the special developed astrogeodetic methodology permit the accurate (some arc seconds) determination of a monument's orientation. Additionally this fact may be also a long discussion between archaeologists, archaeoastronomers and humanists.