Investigation of UAVs mapping methods and spatio-temporal geovisualization for geosites management

The dissertation titled "Investigation of UAVs mapping methods and spatio-temporal geovisualization for geosites management" aims to contribute to the science of cartography by investigating issues regarding 3D mapping and spatio-temporal geovisualization using augmented and virtual reality techniques for the management of areas of geological importance. Divided into three distinct parts for each research question, the work studies the application of cartographic scale principles to issues of data collection via UAVs, the geovisualization of cartographic results obtained through augmented and virtual reality techniques and the rendition of the geovisualizations through evaluation. The implementation of existing and proven cartographic principles in modern imaging media and technologies, as well as the development of new cartographic methods are key challenges in current and future research. This topic is becoming more complex with the emergence of new technologies and techniques in data acquisition and geovisualization, such as UAVs and virtual reality. The need therefore arises for the development of a methodology that combines data collection with UAVs and the geovisualization of cartographic results in virtual and augmented environments, considering basic cartographic principles and the concept of cartographic scale. Initially, the bibliography is extensively reviewed regarding the scale, cartographic data, the fundamental cartographic principles, and the evolution of the science of cartography in recent years. The contribution of modern technological means to the science of cartography and its transition to the digital age are also referenced. In more detail, the utilization of cartographic results and modern interactive geovisualizations in issues related to the management of geological heritage and Geoparks is examined. The literature and scientific references studied in the framework of this doctoral thesis, lack a single methodology that applies to the five basic stages of the integrated mapping of areas of high geological importance. Therefore, a methodology with the following stages is developed and proposed: a) study of issues of scale, b) data collection via UAVs, c) data processing and creation of cartographic results, d) design and development of geovisualizations with augmented and virtual reality techniques and d) evaluation of geovisualizations through experiments on user experience. The first stage examines issues of geographic and cartographic scale of the Lesvos Geopark geosites, classifying them into five categories. The geosites' categorization leads to the calculation of the appropriate spatial resolution and flight characteristics for their 3D mapping, such as the flight altitude, camera angle and the UAVs flight trajectory. In addition, an online cartographic application was developed, which provides information on the acquisition of high-resolution images for the 3D mapping of all geosites of the Lesvos Geopark. The flight planning was followed by the collection of high-resolution images for the 3D mapping of five geosites, one from each geographic scale category. The data were processed using computer vision and 3D graphics algorithms to generate 2D and 3D cartographic results. The cartographic results were: i) 2D orthophoto maps, ii) digital relief models, iii) 3D point clouds and iv) 3D models with photorealistic texture. All results were georeferenced with ground position measurements obtained via a differential receiver. The next stage of the methodology consists of the design of modern interactive geovisualizations with augmented and virtual reality techniques. Specifically, five augmented reality applications that corresponded to the five 3D mapped geosites were developed, along with two virtual reality applications. Virtual reality applications focus on a specific geosite that has been mapped over time and significant changes are identified both in its topography and in its configuration in a visitable location. The last stage focuses on the evaluation of cartographic results and geovisualizations developed in the framework of the thesis through user experience experiments, in the form of lectures, aiming at the geoeducation of postgraduate students. More specifically, four lectures were designed in various presentation styles: i) with physical presence in the field, ii) remotely (distance learning), iii) inside a classroom and iv) with virtual reality techniques. All lectures utilized the cartographic results and the geovisualizations obtained from data collected by UAVs. At the end of the lectures the participants filled a specially designed questionnaire. This was followed by the analysis of the questionnaires using statistical methods and spatial analysis methods, resulting in the conclusions on the contribution of geovisualization to geoeducation and to the participants' spatial perception. In summary, complex geomorphological structures, such as the geoparks of the Lesvos Geopark, require specialized planning in the procedures of data acquisition with UAVs, considering their geographic and cartographic scale for their efficient 3D mapping. Furthermore, the research demonstrates the levels at which the concept of cartographic scale is transferred to geovisualizations of augmented and virtual reality, both at the level of analysis of 3D models and that of information communication, contributing to the understanding of space and the learning experience. In conclusion, both the cartographic results and the 2D and 3D geovisualizations can effectively contribute to geological heritage management processes and offer important data and information to the management institutions and the visitors of the Lesvos Geopark.Η διδακτορική διατριβή με τίτλο «Διερεύνηση μεθόδων χαρτογράφησης με ΣμηΕΑ και χωροχρονικής γεωοπτικοποίησης για τη διαχείριση γεωτόπων», επιχειρεί να συμβάλλει στην επιστήμη της Χαρτογραφίας διερευνώντας ζητήματα αναφορικά με την 3Δ χαρτογράφηση και χωροχρονική γεωοπτικοποίηση, με τη χρήση τεχνικών επαυξημένης και εικονικής πραγματικότητας για τη διαχείριση περιοχών υψηλής γεωλογικής σημασίας. Χωρισμένη σε τρία διακριτά μέρη, βασισμένα στα ερευνητικά ερωτήματα, μελετά την εφαρμογή των αρχών της χαρτογραφικής κλίμακας σε ζητήματα συλλογής δεδομένων με τη χρήση ΣμηΕΑ, την γεωοπτικοποίηση των χαρτογραφικών αποτελεσμάτων που προκύπτουν με την αξιοποίηση τεχνικών επαυξημένης και εικονικής πραγματικότητας και την απόδοση των γεωοπτικοποιήσεων μέσω αξιολόγησης. Η μεταφορά υφιστάμενων, αποδεδειγμένων χαρτογραφικών αρχών στα σύγχρονα μέσα και τεχνολογίες απεικόνισης, καθώς και η ανάπτυξη νέων χαρτογραφικών μεθόδων αποτελούν βασικές προκλήσεις για την τρέχουσα και μελλοντική έρευνα. Το συγκεκριμένο θέμα γίνεται όλο και πιο σύνθετο με την εμφάνιση σύγχρονων εργαλείων και μέσων στη συλλογή δεδομένων και γεωοπτικοποίησης, όπως τα ΣμηΕΑ και η εικονική πραγματικότητα. Προκύπτει συνεπώς η ανάγκη για την ανάπτυξη μεθοδολογίας που να συνδυάζει την συλλογή δεδομένων με τη χρήση ΣμηΕΑ και την γεωοπτικοποίηση των χαρτογραφικών αποτελεσμάτων σε εικονικά και επαυξημένα περιβάλλοντα λαμβάνοντας υπόψη τις βασικές χαρτογραφικές αρχές και την έννοια της χαρτογραφικής κλίμακας. Αρχικά πραγματοποιείται εκτενής βιβλιογραφική ανασκόπηση αναφορικά με τις θεμελιώδεις χαρτογραφικές αρχές αλλά και για την εξέλιξη της επιστήμης της Χαρτογραφίας τα τελευταία χρόνια. Επιπλέον, μελετήθηκε η συμβολή των συγχρόνων τεχνολογικών μέσων στην επιστήμη της Χαρτογραφίας και η μετάβαση της στην ψηφιακή εποχή. Αναλυτικότερα, εξετάζεται η αξιοποίηση των χαρτογραφικών αποτελεσμάτων και των σύγχρονων διαδραστικών γεωοπτικοποιήσεων σε ζητήματα σχετικά με τη διαχείριση της γεωλογικής κληρονομιάς και των Γεωπάρκων. Βάσει της βιβλιογραφίας και των ακαδημαϊκών - επιστημονικών αναφορών που μελετήθηκαν στο πλαίσιο της διδακτορικής διατριβής εντοπίστηκε η έλλειψη μιας ενιαίας μεθοδολογίας που να καλύπτει τα πέντε βασικά στάδια της ολοκληρωμένης χαρτογράφησης περιοχών υψηλής γεωλογικής σημασίας. Συνεπώς, στην παρούσα διατριβή αναπτύσσεται και προτείνεται μεθοδολογία με τα εξής στάδια: α) μελέτη ζητημάτων κλίμακας, β) συλλογή δεδομένων με τη χρήση ΣμηΕΑ, γ) επεξεργασία δεδομένων και δημιουργία χαρτογραφικών αποτελεσμάτων, δ) σχεδιασμός και ανάπτυξη γεωοπτικοποιήσεων με τεχνικές επαυξημένης και εικονικής πραγματικότητας και δ) αξιολόγηση των γεωοπτικοποιήσεων μέσω πειραμάτων εμπειρίας χρήστη.Το πρώτο στάδιο της διατριβής εξετάζει ζητήματα γεωγραφικής και χαρτογραφικής κλίμακας των γεωτόπων του Γεωπάρκου Λέσβου, ταξινομώντας τους σε πέντε κατηγορίες. Οι κατηγορίες οδηγούν στον υπολογισμό της αντίστοιχης χωρικής ανάλυσης και των κατάλληλων χαρακτηριστικών πτήσης, όπως το ύψος πτήσης, η γωνία της κάμερας και τη διαδρομή του ΣμηΕΑ με σκοπό την 3Δ χαρτογράφηση τους. Επιπλέον, αναπτύχθηκε διαδικτυακή χαρτογραφική εφαρμογή στην οποία συγκεντρώνονται και παρέχονται πληροφορίες αναφορικά με τον τρόπο συλλογής εικόνων υψηλής ανάλυσης για την 3Δ χαρτογράφηση όλων των γεωτόπων του Γεωπάρκου Λέσβου. Μετά τον σχεδιασμό των πτήσεων ακολούθησε η συλλογή εικόνων υψηλής ανάλυσης για την 3Δ χαρτογράφηση πέντε γεωτόπων, έναν από κάθε κατηγορία γεωγραφικής κλίμακας. Τα δεδομένα που συλλέχθησαν επεξεργάστηκαν με τη χρήση αλγορίθμων υπολογιστικής όρασης και 3Δ γραφικών για τη δημιουργία 2Δ και 3Δ χαρτογραφικών αποτελεσμάτων. Τα χαρτογραφικά αποτελέσματα ήταν: i) 2Δ ορθοφωτοχάρτες, ii) ψηφιακά μοντέλα αναγλύφου, iii) 3Δ νέφη σημείων και iv) 3Δ μοντέλα με φωτορεαλιστική υφή. Όλα τα αποτελέσματα γεωαναφέρθηκαν με επίγειες μετρήσεις προσδιορισμού θέσης οι οποίες λήφθηκαν με τη χρήση διαφορικού δέκτη. Το επόμενο στάδιο της μεθοδολογίας αναφέρεται στο σχεδιασμό σύγχρονων διαδραστικών γεωοπτικοποιήσεων με τεχνικές επαυξημένης και εικονικής πραγματικότητας. Συγκεκριμένα αναπτύχθηκαν πέντε εφαρμογές επαυξημένης πραγματικότητας που αντιστοιχούσαν στους πέντε γεωτόπους που χαρτογραφήθηκαν 3Δ και δυο εφαρμογές εικονικής πραγματικότητας. Οι εφαρμογές εικονικής πραγματικότητας εστιάζουν σε ένα συγκεκριμένο γεώτοπο ο οποίος χαρτογραφήθηκε διαχρονικά και εντοπίζονται σημαντικές μεταβολές τόσο στην τοπογραφία του όσο και στη διαμόρφωση του σε επισκέψιμη θέση. Το τελευταίο στάδιο επικεντρώνεται στην αξιολόγηση των χαρτογραφικών αποτελεσμάτων και των γεωοπτικοποιήσεων που αναπτύχθηκαν στο πλαίσιο της διδακτορικής διατριβής μέσω πειραμάτων εμπειρίας χρήστη υπό τη μορφή διαλέξεων με στόχο την γεωεκπαίδευση μεταπτυχιακών φοιτητών. Αναλυτικότερα, πραγματοποιήθηκαν τέσσερις διαλέξεις με διαφορετικό τρόπο παρουσίασης: i) με φυσική παρουσία στο πεδίο, ii) με εξ αποστάσεως μέσα (τηλεκπαίδευση), iii) δια ζώσης σε αίθουσα και iv) με τεχνικές εικονικής πραγματικότητας. Σε όλες τις διαλέξεις αξιοποιήθηκαν τα χαρτογραφικά αποτελέσματα και οι γεωοπτικοποιήσεις που προέκυψαν από τα δεδομένα που συλλέχθησαν με τη χρήση ΣμηΕΑ ενώ στο τέλος οι συμμετέχοντες συμπλήρωσαν ένα ειδικά διαμορφωμένο ερωτηματολόγιο. Ακολούθησε η ανάλυση των ερωτηματολογίων με στατιστικές μεθόδους και με μεθόδους χωρικής η οποία οδήγησε σε συμπεράσματα σχετικά με τη συμβολή των γεωοπτικοποίηση στη γεωεκπαίδευση και στη χωρική αντίληψη των συμμετεχόντων. Η παρούσα διατριβή καταλήγει στο συμπέρασμα πως οι σύνθετες γεωμορφολογικά δομές, όπως οι γεώτοποι του Γεωπάρκου Λέσβου, απαιτούν εξειδικευμένο σχεδιασμό στις διαδικασίες συλλογής δεδομένων με ΣμηΕΑ, λαμβάνοντας υπόψη τη γεωγραφική και χαρτογραφική τους κλίμακα για την αποδοτική 3Δ χαρτογράφηση τους. Επιπλέον, από την έρευνα που διεξήχθη προκύπτει ότι η έννοια της χαρτογραφικής κλίμακας μεταφέρεται στις γεωοπτικοποιήσεις επαυξημένης και εικονικής πραγματικότητας τόσο σε επίπεδο ανάλυσης των 3Δ μοντέλων όσο και σε επίπεδο επικοινωνίας της πληροφορίας, συμβάλλοντας στην κατανόηση του χώρου και την εμπειρία μάθησης. Τέλος, συμπεραίνεται ότι τόσο τα χαρτογραφικά αποτελέσματα όσο και οι 2Δ και 3Δ γεωοπτικοποιήσεις δύναται να συνεισφέρουν αποτελεσματικά σε διαδικασίες διαχείρισης της γεωλογικής κληρονομίας και να προσφέρουν σημαντικά στοιχεία και πληροφορίες στους φορείς διαχείρισης και στους επισκέπτες του Γεωπάρκου Λέσβου

Scale-variant flight planning for the creation of 3d geovisualization and augmented reality maps of geosites: The case of voulgaris gorge, lesvos, Greece

The purpose of this paper was to study the influence of cartographic scale and flight design on data acquisition using unmanned aerial systems (UASs) to create augmented reality 3D geovisualization of geosites. The relationship between geographical and cartographic scales, the spatial resolution of UAS-acquired images, along with their relationship with the produced 3D models of geosites, were investigated. Additionally, the lighting of the produced 3D models was examined as a key visual variable in the 3D space. Furthermore, the adaptation of the 360◦ panoramas as environmental lighting parameters was considered. The geosite selected as a case study was the gorge of the river Voulgaris in the western part of the island of Lesvos, which is located in the northeastern part of the Aegean Sea in Greece. The methodology applied consisted of four pillars: (i) scale-variant flight planning, (ii) data acquisition, (iii) data processing, (iv) AR, 3D geovisualization. Based on the geographic and cartographic scales, the flight design calculates the most appropriate flight parameters (height, speed, and image overlaps) to achieve the desired spatial resolution (3 cm) capable of illustrating all the scale-variant details of the geosite when mapped in 3D. High-resolution oblique aerial images and 360◦ panoramic aerial images were acquired using scale-variant flight plans. The data were processed using image processing algorithms to produce 3D models and create mosaic panoramas. The 3D geovisualization of the geosite selected was created using the textured 3D model produced from the aerial images. The panoramic images were converted to high-dynamic-range image (HDRI) panoramas and used as a background to the 3D model. The geovisualization was transferred and displayed in the virtual space where the panoramas were used as a light source, thus enlightening the model. Data acquisition and flight planning were crucial scale-variant steps in the 3D geovisualization. These two processes comprised the most important factors in 3D geovisualization creation embedded in the virtual space as they designated the geometry of the 3D model. The use of panoramas as the illumination parameter of an outdoor 3D scene of a geosite contributed significantly to its photorealistic performance into the 3D augmented reality and virtual space

VR Multiscale Geovisualization Based on UAS Multitemporal Data: The Case of Geological Monuments

Technological progress in Virtual Reality (VR) and Unmanned Aerial Systems (UASs) offers great advantages in the field of cartography and particularly in the geovisualization of spatial data. This paper investigates the correlation between UAS flight characteristics for data acquisition and the quality of the derived maps and 3D models of geological monuments for VR geovisualization in different scales and timeframes. In this study, we develop a methodology for mapping geoheritage monuments based on different cartographic scales. Each cartographic scale results in diverse orthophotomaps and 3D models. All orthophotomaps and 3D models provide an optimal geovisualization, combining UAS and VR technologies and thus contributing to the multitemporal 3D geovisualization of geological heritage on different cartographic scales. The study area selected was a fossilite ferrous site located in Lesvos Geopark, UNESCO. The study area contains a fossil site surrounding various findings. The three distinct scales that occur are based on the object depicted: (i) the fossilite ferrous site (1:120), (ii) the fossil root system (1:20), and (iii) individual fossils (≥1:10). The methodology followed in the present research consists of three main sections: (a) scale-variant UAS data acquisition, (b) data processing and results (2D–3D maps and models), and (c) 3D geovisualization to VR integration. Each different mapping scale determines the UAS data acquisition parameters (flight pattern, camera orientation and inclination, height of flight) and defines the resolution of the 3D models to be embedded in the VR environment. Due to the intense excavation of the study area, the location was spatiotemporally monitored on the cartographic scale of 1:120. For the continuous monitoring of the study area, four different UASs were also used. Each of them was programmed to fly and acquire images with a constant ground sampling distance (GSD). The data were processed by image-based 3D modeling and computer vision algorithms from which the 3D models and orthophotomaps were created and used in the VR environment. As a result, a VR application visualizing multitemporal data of geoheritage monuments across three cartographic scales was developed

Building Change Detection Based on a Gray-Level Co-Occurrence Matrix and Artificial Neural Networks

The recovery phase following an earthquake event is essential for urban areas with a significant number of damaged buildings. A lot of changes can take place in such a landscape within the buildings’ footprints, such as total or partial collapses, debris removal and reconstruction. Remote sensing data and methodologies can considerably contribute to site monitoring. The main objective of this paper is the change detection of the building stock in the settlement of Vrissa on Lesvos Island during the recovery phase after the catastrophic earthquake of 12 June 2017, through the analysis and processing of UAV (unmanned aerial vehicle) images and the application of Artificial Neural Networks (ANNs). More specifically, change detection of the settlement’s building stock by applying an ANN on Gray-Level Co-occurrence Matrix (GLCM) texture features of orthophotomaps acquired by UAVs was performed. For the training of the ANN, a number of GLCM texture features were defined as the independent variable, while the existence or not of structural changes in the buildings were defined as the dependent variable, assigning, respectively, the values 1 or 0 (binary classification). The ANN was trained based on the Levenberg–Marquardt algorithm, and its ability to detect changes was evaluated on the basis of the buildings’ condition, as derived from the binary classification. In conclusion, the GLCM texture feature changes in conjunction with the ANN can provide satisfactory results in predicting the structural changes of buildings with an accuracy of almost 92%

A KG-Based Integrated UAV Approach for Engineering Semantic Trajectories in the Cultural Heritage Documentation Domain

Data recordings of the movement of vehicles can be enriched with heterogeneous and multimodal data beyond latitude, longitude, and timestamp and enhanced with complementary segmentations, constituting a semantic trajectory. Semantic Web (SW) technologies have been extensively used for the semantic integration of heterogeneous and multimodal movement-related data, and for the effective modeling of semantic trajectories, in several domains. In this paper, we present an integrated solution for the engineering of cultural heritage semantic trajectories generated from unmanned aerial vehicles (UAVs) and represented as knowledge graphs (KGs). Particularly, this work is motivated by, and evaluated based on, the application domain of UAV missions for documenting regions/points of cultural heritage interest. In this context, this research work extends our previous work on UAV semantic trajectories, contributing (a) an updated methodology for the engineering of semantic trajectories as KGs (STaKG), (b) an implemented toolset for the management of KG-based semantic trajectories, (c) a refined ontology for the representation of knowledge related to UAV semantic trajectories and to cultural heritage documentation, and (d) the application and evaluation of the proposed methodology, the developed toolset, and the ontology within the domain of UAV-based cultural heritage documentation. The evaluation of the integrated UAV solution was achieved by exploiting real datasets collected during three UAV missions to document sites of cultural interest in Lesvos, Greece, i.e., the UNESCO-protected petrified forest of Lesvos Petrified Forest/Geopark, the village of Vrissa, and University Hill

Scale issues for geoheritage 3D mapping: The case of Lesvos Geopark, Greece

A geopark can be composed of many individual geosites of various geographical scales, thus, categorization according to cartographic scale is crucial for their 3D mapping. The UNESCO Global Geopark of the island of Lesvos in the north-east Aegean, Greece, is a distinctive example of this type of geopark as it contains many unique geosites that vary in geographical scale. The geographical scale is interconnected with the cartographic scale in which the geosite is visualized. The desired cartographic scale is an essential user requirement within an unmanned aerial vehicle's (UAVs) 3D mapping project as the basis for the data acquisition strategy. This research investigates the scale issues in 3D mapping of geosites. Furthermore, it contributes to the incorporation of the geographic and cartographical scales in association with UAV flight parameters such as Ground Sample Distance (GSD), altitude, gimbal pitch, orientation, and front and side overlapping. A total of 132 geosites located in Lesvos Geopark are being studied to determine the flight parameters of three different UAVs and their camera characteristics. The methodology followed to collect very high-resolution images suitable for 3D mapping consists of five main stages: i) determining the geographical scale of each geosite, ii) defining the cartographic scale of all geosites, iii) calculation of the GSD based on cartographic scale, iv) calculation of UAV flight altitude and flight characteristics, and v) classification of geosites based on the flight characteristics for their 3D mapping. Five geographic (G1: 100 ha) and five cartographic (C1: > 1:50, C2: 1:50–1:100, C3: 1:100–1:250, C4: 1:250–1:500, C5: < 1:500) categories were defined based on the geosites' size and extent. The combination of the two scales determines the most efficient flight characteristics and optimally acquires very high-resolution images required for the 3D mapping of the selected geosites. Finally, the categorization and characteristics of flights for data collection for high-resolution 3D mapping are collected and presented in a web application. The web application is addressed to the management board of Lesvos Geopark and supports the decision-making processes on mapping geosites using UAVs

Geovisualization of the excavation process in the Lesvos petrified forest, Greece using augmented reality

Augmented reality (AR), in conjunction with 3D geovisualization methods, can provide significant support in monitoring geoconservation activities in protected geosites, such as the excavation process in fossil sites. The excavation process requires a monitoring methodology that will provide a complete and accurate overview of the fossils, their dimensions, and location within the different pyroclastic horizons, and the progress of the excavation works. The main purpose of this paper is the development of a user-friendly augmented map application, specifically designed for tracking the position of petrified tree trunks, providing information for their geometric features, and mapping the spatiotemporal changes occurring in the surrounding space. It also aims to probe whether the rapid acquisition of a 4K video can generate cartographic derivatives of petrified findings during a geosite excavation. A database accumulated 2D and 3D cartographic information, while the geovisualization environment displayed the surface alterations, at two scales: a) 1:500 (excavation area) and b) 1:50 (trench level). Unmanned aerial systems (UASs), used for data acquisition in three excavation periods, consisted of two flights at two different altitudes: one to record changes throughout the study area and the other to provide information on trunks at trench level, via a high-resolution (4K) video. Image-based 3D modeling followed, in which image georeferencing was conducted with ground control points (GCPs). Finally, 2D and 3D geovisualizations were created to depict the excavation changes through time. The cartographic products generated at two cartographic scales depicted the spatiotemporal changes of the excavation

A KG-Based Integrated UAV Approach for Engineering Semantic Trajectories in the Cultural Heritage Documentation Domain

Data recordings of the movement of vehicles can be enriched with heterogeneous and multimodal data beyond latitude, longitude, and timestamp and enhanced with complementary segmentations, constituting a semantic trajectory. Semantic Web (SW) technologies have been extensively used for the semantic integration of heterogeneous and multimodal movement-related data, and for the effective modeling of semantic trajectories, in several domains. In this paper, we present an integrated solution for the engineering of cultural heritage semantic trajectories generated from unmanned aerial vehicles (UAVs) and represented as knowledge graphs (KGs). Particularly, this work is motivated by, and evaluated based on, the application domain of UAV missions for documenting regions/points of cultural heritage interest. In this context, this research work extends our previous work on UAV semantic trajectories, contributing (a) an updated methodology for the engineering of semantic trajectories as KGs (STaKG), (b) an implemented toolset for the management of KG-based semantic trajectories, (c) a refined ontology for the representation of knowledge related to UAV semantic trajectories and to cultural heritage documentation, and (d) the application and evaluation of the proposed methodology, the developed toolset, and the ontology within the domain of UAV-based cultural heritage documentation. The evaluation of the integrated UAV solution was achieved by exploiting real datasets collected during three UAV missions to document sites of cultural interest in Lesvos, Greece, i.e., the UNESCO-protected petrified forest of Lesvos Petrified Forest/Geopark, the village of Vrissa, and University Hill

Post-earthquake recovery phase monitoring and mapping based on UAS data

Geoinformatics plays an essential role during the recovery phase of a post-earthquake situation. The aim of this paper is to present the methodology followed and the results obtained by the utilization of Unmanned Aircraft Systems (UASs) 4K-video footage processing and the automation of geo-information methods targeted at both monitoring the demolition process and mapping the demolished buildings. The field campaigns took place on the traditional settlement of Vrisa (Lesvos, Greece), which was heavily damaged by a strong earthquake (Mw=6.3) on June 12th, 2017. For this purpose, a flight campaign took place on 3rd February 2019 for collecting aerial 4K video footage using an Unmanned Aircraft. The Structure from Motion (SfM) method was applied on frames which derived from the 4K video footage, for producing accurate and very detailed 3D point clouds, as well as the Digital Surface Model (DSM) of the building stock of the Vrisa traditional settlement, twenty months after the earthquake. This dataset has been compared with the corresponding one which derived from 25th July 2017, a few days after the earthquake. Two algorithms have been developed for detecting the demolished buildings of the affected area, based on the DSMs and 3D point clouds, correspondingly. The results obtained have been tested through field studies and demonstrate that this methodology is feasible and effective in building demolition detection, giving very accurate results (97%) and, in parallel, is easily applicable and suit well for rapid demolition mapping during the recovery phase of a post-earthquake scenario. The significant advantage of the proposed methodology is its ability to provide reliable results in a very low cost and time-efficient way and to serve all stakeholders and national and local organizations that are responsible for post-earthquake management