A. Georgopoulos

Digital image processing as a tool for pavement distress evaluation

Abstract The information obtained through accurate condition assessment of pavement surface distress data is needed as an essential input to any decision making process concerning pavement management policy. At the same time technological advances in automated inspection systems provide the opportunity to automate the collection and evaluation of the pavement surface condition. In this paper a method developed jointly by the Laboratories of Highway Engineering and Photogrammetry of the National Technical University of Athens is described and proposed. The method involves digital image processing techniques to provide suitable digital imagery as input to specialised software developed especially for this project. This software determines objectively and fully automatically the type, the extent and the severity of surface crackings for flexible road pavements. The proposed method presenten substantial agreement, when compared with systematic visual ratings of existing pavement crackings carried out according to the internationally accepted requirements for airfield and road pavement of the Federal Aviation Administration (FAA).

Innovative Techniques for the Acquisition and Processing of Multisource Data for the Geometric Documentation of Monuments

Documenting the past of mankind comprises, among other activities, the survey of monuments and cultural artefacts, for long provided by archaeologists and architects using traditional methods. However, due to the recent major technological advances in surveying, photogrammetric and laser scanning methods, surveyors are enabled to produce recording materials and end products, which surpass by far the traditional line drawings in terms of accuracy and completeness. These methodologies are able to offer products like orthophotos, raster developments, 3D representations and realistic visualizations as well as augmented reality tours. This paper investigates the principles and capabilities of contemporary and technologically advanced methods in: capturing huge amount of detailed, accurate and reliable 3D data; modeling of existing and virtual reality; management of 3D or image-based databases. Several examples covering a broad variety of cases, regarding the historical era, the size and the complexity of the monument and also the final products are presented.

Documenting a Unesco Wh Site in Cyprus with Complementary Techniques

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 technique with Mencis ZS...

Documentation of a submerged monument using improved two media techniques

The rapid developments of technology in recent years have opened new horizons in Photogrammetry, overcoming obstacles sometimes insurmountable, reducing time and increasing accuracy of results. However, while the continuous development of close-range Photogrammetric methods for the geometric documentation of monuments on land and sea seem to go hand in hand, techniques for capturing submerged archaeological sites especially when situated at shallow depths are inadequate while application of traditional methods is impossible or uneconomical. This paper describes the improvement of two-media (through air and water) photogrammetric techniques for the documentation of a submerged archaeological site of Epidaurus, Greece, at a depth ranging from 0.5 to 2 meters. Specific reference is made to the various problems caused by the presence of water and how they were addressed. Errors in depth determination caused by waves, colour absorption and chromatic aberration are also addressed. Particular attention is given to the effects of refraction at the air/water interface on the Collinearity Condition. The various attempts are presented, analysed and evaluated. Finally, ortho-images have been generated and cross section data were collected in order to perform the documentation.

Exploitation of thermal imagery for the detection of pathologies in monuments

Documentation of monuments includes not only geometric analysis but also the detection of alterations and pathologies to define proper actions for protection and preservation. Several pathologies can be found on facades such as moisture, detachments, leaks and replacements. Multispectral techniques can help users to detect and determine these phenomena. Thermography is a non-intrusive imaging technique that allows the inspection of different materials and related issues based on their temperature. It has the advantage of reaching unapproachable areas onto and below the surface. However, there are still many issues in thermography when applied to cultural heritage surveys. Depending on the application, multitemporal images can be captured and combined with conventional images to analyse its state of conservation. This paper presents an approach based on multitemporal thermal imagery to detect alterations on building facades. Methods and tools of multispectral analysis targeting the detection of alterations and pathologies are presented and evaluated.

Contemporary Digital Methods for the Geometric Documentation of Churches in Cyprus

Recent advances in digital methods incorporating information technology have enabled the traditional surveyor and monument recorder to work faster, more accurately and in an automated way in order to produce advanced digital products, more versatile and more useful to the end users. Such methods include tacheometry, digital photogrammetry, as image-based method, terrestrial laser scanning and the development of specialized software in order to fully exploit the digital data acquisition. Usually, a combination of these methods gives the most efficient cost benefit results, by providing 2D vector and raster products and 3D textured models. In this paper two examples of the implementation of these methods in the geometric documentation of two churches, both significant for the history of Cyprus, are presented. It is concerned with the churches of Virgin Mary (Panayia) Podithou, in Galata and St. George Nikoxylitis in Droushia. The applied methodology, using classical and contemporary techniques of commercial and in-house developed software is presented. Comparative tests for the achieved accuracies and the completeness of each methods products have been made, and their merits and usefulness are explained.

Towards an archaeological index: identification of the spectral regions of stress vegetation due to buried archaeological remains

This paper aims to introduce the spectral characteristics of a new Archaeological Index for supporting remote sensing applications in archaeological research. This index will be able to enhance crop marks, observed in satellite images, which are related to buried archaeological remains. For the aims of the research, ground spectral signatures were acquired from two agricultural areas of Cyprus (Alampra and Acheleia), specifically constructed in order to simulate buried archaeological remains. A complete phenological cycle of barley and wheat crops was recorded using the GER 1500 spectroradiometer with spectral range from 350 --- 1050 nm (visible --- near infrared spectrum). Correlation regression analysis and evaluation separability indices have shown that results are similar for both sites ---regardless crop type. The spectral sensitivity, for enhancement crop marks, was detected at the red edge and near infrared spectrum (≈ 700 and ≈ 800 nm).

Serious Games at the Service of Cultural Heritage and Tourism

Recent advances in contemporary technologies have greatly affected everyday life. In the field of cultural heritage, ICT (Information Communication Technologies) have enabled applications for the thorough multi-dimensional geometric documentation and consequently for the realistic visualization of monuments and artifacts. At the same time the driving force of technology is the game industry. Games and especially Serious Games can be put at the service of cultural heritage, education and tourism exploiting the aforementioned advances and especially the textured three dimensional models. They constitute an attractive platform enabling people to get acquainted with the heritage treasures and get motivated to visit the place and admire the treasures live. In this paper this technological merger is explained and three interconnected applications are presented in order to prove the concept through these implementations. They concern the development of Serious Games for an archaeological site, which aim at the trivial or more specialized information dissemination about that site, while familiarizing the prospect visitor with the environment and the monuments of the site offering the possibility of virtually visiting them. Moreover the development of a virtual museum within a game development environment is presented, which provides the possibility to learn about each exhibit, but also it offers the opportunity to the user to closely examine the exhibits through rotating their three dimensional models. All these examples use realistic models produced for documentation purposes, which convey the real impression of the monuments visualized to the user.

Virtual reconstruction of the ancient state of a ruined church

Three dimensional virtual models can represent both the existing and the already destroyed architectural heritage. This project deals with the 3D reconstruction and representation of the church of San Prudencios Monastery in La Rioja (Spain) as it is supposed to be during the 15th century. Today the monument is totally in ruins; hence severe reconstruction was needed. This is an exemplary project of close collaboration of different scientific fields. Surveying data of the monument itself and of the wider area around it, but also architectural and archaeological data were collected in situ. It was not possible from the current situation to conclude about the exact form, style and representation of the monument; hence a large part of the project is based on assumptions which have a sound scientific base. Because of the multisource data there was need to define specific criteria by which every data source was evaluated.

Comparison of 3D representations depicting micro folds: overlapping imagery vs. time-of-flight laser scanner

A relatively new field of interest, which continuously gains grounds nowadays, is digital 3D modeling. However, the methodologies, the accuracy and the time and effort required to produce a high quality 3D model have been changing drastically the last few years. Whereas in the early days of digital 3D modeling, 3D models were only accessible to computer experts in animation, working many hours in expensive sophisticated software, today 3D modeling has become reasonably fast and convenient. On top of that, with online 3D modeling software, such as 123D Catch, nearly everyone can produce 3D models with minimum effort and at no cost. The only requirement is panoramic overlapping images, of the (still) objects the user wishes to model. This approach however, has limitations in the accuracy of the model. An objective of the study is to examine these limitations by assessing the accuracy of this 3D modeling methodology, with a Terrestrial Laser Scanner (TLS). Therefore, the scope of this study is to present and compare 3D models, produced with two different methods: 1) Traditional TLS method with the instrument ScanStation 2 by Leica and 2) Panoramic overlapping images obtained with DSLR camera and processed with 123D Catch free software. The main objective of the study is to evaluate advantages and disadvantages of the two 3D model producing methodologies. The area represented with the 3D models, features multi-scale folding in a cipollino marble formation. The most interesting part and most challenging to capture accurately, is an outcrop which includes vertically orientated micro folds. These micro folds have dimensions of a few centimeters while a relatively strong relief is evident between them (perhaps due to different material composition). The area of interest is located in Mt. Hymittos, Greece.