ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, 2016
Photogrammetry is a valid alternative solution to linear variable differential transformer (LVDT)... more Photogrammetry is a valid alternative solution to linear variable differential transformer (LVDT) measurements in structural testing in laboratory conditions. Although the use of LVDTs boasts a high degree of accuracy, on the other hand it is limiting as it offers measurements between two points and it thus might be unable to capture localized deformations and strains over a bigger area of a structural specimen. In this aspect photogrammetry seems to offer certain advantages. Commercial solutions provide limited testing envelopes, while on the other hand, the wide range on new materials need more versatile techniques. Based on the need to develop an in-house photogrammetric toolbox to support several structural and material experiments in the department Advanced Pore Morphology (APM) aluminium foam specimens developed at Fraunhofer IFAM in Germany and cured at CUT, were tested under monotonic compressive load. Data acquisition, analysis and results, along with lessons learnt from the process are presented in this work.
The global breeding population of Eleonora’s Falcon (Falco eleonorae) is distributed from the Can... more The global breeding population of Eleonora’s Falcon (Falco eleonorae) is distributed from the Canary Islands in the west, across the Mediterranean Sea, to Cyprus in the east. The remoteness of nesting colonies, which are predominantly located on sea cliffs and islets, renders breeding success estimation a challenging task, requiring a composite approach to assess each of the breeding stages. Early estimates of the breeding success of Eleonora’s Falcon suggested that the Akrotiri colony in Cyprus had the lowest breeding success among all the colonies throughout the species’ breeding range, at a level seemingly unsustainable, suggesting the colony might have been in danger of gradual extinction. Here we use a diversity of survey methods including boat, ground, and aerial surveys, with the incorporation of photography and photogrammetry, to reassess the breeding success and the effect of nest characteristics on the Eleonora’s Falcon breeding population in Cyprus. During a 6-yr study, w...
Earth dams are massive water-retaining structures that are used widely in the world for irrigatio... more Earth dams are massive water-retaining structures that are used widely in the world for irrigation, water supply and hydroelectric energy generation. Many such dams are built every year and the International Committee on Large Dams (ICOLD) has gathered together experts from the world to work on preparing guidelines for design, construction and monitoring of such massive infrastructure. A potential failure of a large dam may potentially have significant effects on a huge area downstream, as the sudden release of the large volume of retained water can travel for large distances and destroy entire cities and even result in unfortunate fatalities. It is therefore important to recognise the potential causes of failure of such dams and provide timely and effective measures to prevent any degradation or loss of stability. The main threats for dams are seismic activity, internal erosion, faulting and seasonal climate variations. The latter factor, i.e. climate changes, has not been studied ...
Digital Heritage. Progress in Cultural Heritage: Documentation, Preservation, and Protection, 2016
The project iMARECULTURE is focusing in raising European identity awareness using maritime and un... more The project iMARECULTURE is focusing in raising European identity awareness using maritime and underwater cultural interaction and exchange in Mediterranean Sea. Commercial ship routes joining Europe with other cultures are vivid examples of cultural interaction, while shipwrecks and submerged sites, unreachable to wide public are excellent samples that can benefit from immersive technologies, augmented and virtual reality. The projects aim to bring inherently unreachable underwater cultural heritage within digital reach of the wide public using virtual visits and immersive technologies. Apart from reusing existing 3D data of underwater shipwrecks and sites, with respect to ethics, rights and licensing, to provide a personalized dry visit to a museum visitor or augmented reality to the diver, it also emphasizes on developing pre-and after-encounter of the digital or physical museum visitor. The former one is implemented exploiting geospatial enabled technologies for developing a serious game of sailing over ancient Mediterranean and the latter for an underwater shipwreck excavation game. Both games are realized thought social media, in order to facilitate information exchange among users. The project supports dry visits providing immersive experience through VR Cave and 3D info kiosks on museums or through the web. Additionally, aims to significantly enhance the experience of the diver, visitor or scholar, using underwater augmented reality in a tablet and an underwater housing. The consortium is composed by universities and SMEs with experience in diverse underwater projects, existing digital libraries, and people many of which are divers themselves.
2017 9th International Conference on Virtual Worlds and Games for Serious Applications (VS-Games), 2017
Commercial sea routes joining Europe with other cultures are vivid examples of cultural interacti... more Commercial sea routes joining Europe with other cultures are vivid examples of cultural interaction. In this work, we present a serious game which aims to provide better insight and understanding of seaborne trade mechanisms and seafaring practices in the eastern Mediterranean during the Classical and Hellenistic periods. The game incorporates probabilistic geospatial analysis of possible ship routes through the re-use and spatial analysis from open GIS maritime, ocean, and weather data. These routes, along with naval engineering and sailing techniques from the period, are used as underlying information for the seafaring game. This work is part of the EU-funded project iMareCulture whose purpose is in raising the European identity awareness using maritime and underwater cultural interaction and exchange in the Mediterranean sea.
The use of a square template in least squares image matching has been established as a well known... more The use of a square template in least squares image matching has been established as a well known and tested method. This paper suggests the use of an elliptical template as alternative to the square one. The main stimulus for the adoption of the ellipse was the disturbing shift of the matched point along linear features. When the square template was used around a point in a linear feature, the matched point was not in the correct position, due to slipping along that feature. This phenomenon is expected in least squares matching (LSQM) because all points along the line are similar and hardly distinguishable. Even the use of epipolar geometry cannot solve the ambiguity of this problem, when the linear features are parallel or almost parallel to the epipolar line. The use of a dynamic ellipse oriented with the large axis along the linear feature uses considerably more information, thus strengthening the matching process along that direction. The necessary information about the size, s...
According to UNESCO directives, the documentation of monuments is a complex task, which both terr... more According to UNESCO directives, the documentation of monuments is a complex task, which both terrestrial laser scanning (TLS) and photogrammetry can decisively support. Today, these techniques are considered complementary, as they demonstrate clear advantages and disadvantages to each other, with regard to representation, texture application, data gathering, acquisition and processing time, practicality, accuracy, data density, surface reflectivity and absorption. In an effort to clarify which part should be acquired with which technique, as well as to understand whether one technique has a clear advantage over the other in some specific task of the documentation process, the Church of the Holy Cross in Pelendri, Cyprus, which is a UNESCO World Heritage monument, was selected as a test site. The deliverables are orthophotos, sections, plots and a complete and accurate 3D model of the monument. The whole documentation process has been carried out independently using an image based te...
The Erasmus Intensive Programme “HERICT: ICT at the Service of Cultural Heritage” has brought tog... more The Erasmus Intensive Programme “HERICT: ICT at the Service of Cultural Heritage” has brought together 40 students and 11 Professors from nine different European Universities for two weeks. The central idea of this summer school was Cultural heritage and how this may benefit from the discipline of Geomatics. Hence the students and professors present covered the disciplines of the users, i.e. Archaeologists and Architects, and the providers, i.e. Geomatics specialists. The coexistence of this interdisciplinary group of students and professors for two weeks in a remote and isolated village in Rhodos island has had significant influence. In this paper the experiences gained and the results of this summer school are presented and evaluated.
The need for Digital Elevation Model (DEM) checking has raised since the automated matching techn... more The need for Digital Elevation Model (DEM) checking has raised since the automated matching techniques emerged. The use of reference data is a luxury and therefore cannot be used in all cases. This article presents a completely new mathematical model, which translates discrepancies between two orthophotographs created from different photographs, into precise corrections of the DEM. These corrections are the differences from the real surface and, if applied over the existing DEM, can produce a more accurate one. The mathematical model is straightforward, does not approximate, and therefore there is no need for iterations. In order to test the algorithm a reference DEM has been manually collected and distorted with a known pattern. The corrections produced by the algorithm follow the known pattern. Tests over automatically created DEMs by commercial software has also been made and compared against the reference DTM. Obvious applications include checking of automatically created DEMs, ...
ISPRS Annals of Photogrammetry, Remote Sensing and Spatial Information Sciences
Current advancements on photogrammetric software along with affordability and wide spreading of U... more Current advancements on photogrammetric software along with affordability and wide spreading of Unmanned Aerial Vehicles (UAV), allow for rapid, timely and accurate 3D modelling and mapping of small to medium sized areas. Although the importance and applications of large format aerial overlaps cameras and photographs in Digital Surface Model (DSM) production and LIDAR data is well documented in literature, this is not the case for UAV photography. Additionally, the main disadvantage of photogrammetry is the inability to map the dead ground (terrain), when we deal with areas that include vegetation. This paper assesses the use of near-infrared imagery captured by small UAV platforms to automatically remove vegetation from Digital Surface Models (DSMs) and obtain a Digital Terrain Model (DTM). Two areas were tested, based on the availability of ground reference points, both under trees and among vegetation, as well as on terrain. In addition, RGB and near-infrared UAV photography was ...
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
Underwater archaeological discoveries bring new challenges to the field, but such sites are more ... more Underwater archaeological discoveries bring new challenges to the field, but such sites are more difficult to reach and, due to natural influences, they tend to deteriorate fast. Photogrammetry is one of the most powerful tools used for archaeological fieldwork. Photogrammetric techniques are used to document the state of the site in digital form for later analysis, without the risk of damaging any of the artefacts or the site itself. To achieve best possible results with the gathered data, divers should come prepared with the knowledge of measurements and photo capture methods. Archaeologists use this technology to record discovered arteacts or even the whole archaeological sites. Data gathering underwater brings several problems and limitations, so specific steps should be taken to get the best possible results, and divers should well be prepared before starting work at an underwater site. Using immersive virtual reality, we have developed an educational software to introduce maritime archaeology students to photogrammetry techniques. To test the feasibility of the software, a user study was performed and evaluated by experts. In the software, the user is tasked to put markers on the site, measure distances between them, and then take photos of the site, from which the 3D mesh is generated offline. Initial results show that the system is useful for understanding the basics of underwater photogrammetry.
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
The work presented in this paper investigates the effect of the radiometry of the underwater imag... more The work presented in this paper investigates the effect of the radiometry of the underwater imagery on automating the 3D reconstruction and the produced orthoimagery. Main aim is to investigate whether pre-processing of the underwater imagery improves the 3D reconstruction using automated SfM - MVS software or not. Since the processing of images either separately or in batch is a time-consuming procedure, it is critical to determine the necessity of implementing colour correction and enhancement before the SfM - MVS procedure or directly to the final orthoimage when the orthoimagery is the deliverable. Two different test sites were used to capture imagery ensuring different environmental conditions, depth and complexity. Three different image correction methods are applied: A very simple automated method using Adobe Photoshop, a developed colour correction algorithm using the CLAHE (Zuiderveld, 1994) method and an implementation of the algorithm described in Bianco et al., (2015). ...
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
In this paper, main challenges of underwater photogrammetry in shallow waters are described and a... more In this paper, main challenges of underwater photogrammetry in shallow waters are described and analysed. The very short camera to object distance in such cases, as well as buoyancy issues, wave effects and turbidity of the waters are challenges to be resolved. Additionally, the major challenge of all, caustics, is addressed by a new approach for caustics removal (Forbes et al., 2018) which is applied in order to investigate its performance in terms of SfM-MVS and 3D reconstruction results. In the proposed approach the complex problem of removing caustics effects is addressed by classifying and then removing them from the images. We propose and test a novel solution based on two small and easily trainable Convolutional Neural Networks (CNNs). Real ground truth for caustics is not easily available. We show how a small set of synthetic data can be used to train the network and later transfer the learning to real data with robustness to intra-class variation. The proposed solution resu...
ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences
This paper investigates immersive technologies to increase exploration time in an underwater arch... more This paper investigates immersive technologies to increase exploration time in an underwater archaeological site, both for the public, as well as, for researchers and scholars. Focus is on the Mazotos shipwreck site in Cyprus, which is located 44 meters underwater. The aim of this work is two-fold: (a) realistic modelling and mapping of the site and (b) an immersive virtual reality visit. For 3D modelling and mapping optical data were used. The underwater exploration is composed of a variety of sea elements including: plants, fish, stones, and artefacts, which are randomly positioned. Users can experience an immersive virtual underwater visit in Mazotos shipwreck site and get some information about the shipwreck and its contents for raising their archaeological knowledge and cultural awareness.
The replication (exact copying) of marble museum exhibits using marble powder is being analysed i... more The replication (exact copying) of marble museum exhibits using marble powder is being analysed in this paper. Optical and laser scanners has been used to collect dense point clouds, which form a three-dimensional computer model. This model has been used to physically reconstruct the object using rapid prototyping techniques. Model of objects from 0.15m up to 1.86m have been replicated as examples. The procedure and the problems confronted with the solutions given on each case, along with experience gained are being discussed. Problems concerning accuracy, number of points and formulation of the model are reported. Comparison of the systems in terms of accuracy, speed and functionality is the main concern of this paper. Particular reference is being done to the optical scanner. In order to minimize the number of the photographs, maximize the data collection rate and automate as much as possible the procedure, a slide projector with a grid is being used as the second camera. The proc...
This paper investigates possible solutions to the problem of urban orthophotography. Many efforts... more This paper investigates possible solutions to the problem of urban orthophotography. Many efforts have been made, using all existing software in the Department of Geomatic Engineering, University College London in order to attain the best possible results. Two of the most promising methods, which yield the best results, are analyzed further. New routines were written in C language in addition to the existing software to allow for the special problems that arise in urban areas. The final results overcome the problem of double mapping (or occlusions) and assure that even better results may be expected. A simple accuracy assessment of the results has been made. Difficulties and current limitations are analyzed and presented.
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Papers by D. Skarlatos