Styliani Verykokou

3D Visualization via Augmented Reality: The Case of the Middle Stoa in the Ancient Agora of Athens

Augmented reality is a rapidly evolving technology that enriches reality with computer generated information as well as a powerful tool that provides innovative ways of information access at cultural heritage sites. In this paper, an augmented reality application that allows the visualization of a part of the Middle Stoa in the Ancient Agora of Athens is presented. Users of this application, pointing their tablet PC at the present situation, have the opportunity to see what this building looked like in ancient times, as its three dimensional model is displayed on the camera view of their device, projected on the modern-day ruins.

UAV-based 3D modelling of disaster scenes for Urban Search and Rescue

Natural or man-made disasters often result in trapped victims under rubble piles. In such emergency response situations, Urban Search and Rescue (USaR) teams have to make quick decisions to determine the location of possible trapped humans. The fast 3D modelling of collapsed buildings using images from Unmanned Aerial Vehicles (UAVs) can significantly help the USaR operations and improve disaster response. The apriori establishment of a proper workflow for fast and reliable image-based 3D modelling and the careful parameterization in every step of the photogrammetric process are crucial aspects that ensure the readiness in an emergency situation. This paper evaluates powerful commercial and open-source software for the creation of 3D models of disaster scenes using UAV imagery for rapid response situations and conducts a thorough analysis on the parameters of the various modelling steps that may lead to the desired results for USaR operations. The main result of our analysis is the establishment of optimized photogrammetric procedures with the scope of fast 3D modelling of disaster scenes, to assist USaR teams and increase survival rates.

5D multi-purpose land information system

The complexity of modern urban environments has led to the introduction of 3D Land Information Systems (LISs), which tend to replace traditional 2D LIS architectures for the purposes of urban planning and regeneration, land administration, real estate management and civil development. Both the need for 3D visualization of the geometry of buildings in various time instances through the years and the need for acquisition of 3D models in various levels of detail (LoDs), which not only fulfill the requirements of the various users but also they speed up the visualization process, are obvious. Thus, additional dimensions, that is, for time and scale, need to be supported by a modern LIS. This paper introduces a 5D modelling pipeline that may be adopted by a multi-purpose LIS for the selective creation of 3D models of an urban area in various time instances and at various LoDs, enriched with cadastral and other spatial data. The methodology is based on automatic change detection algorithms for spatial-temporal analysis of the spatial changes that took place in subsequent time periods, using image orientation, dense image matching and structure from motion algorithms; the procedure requires photogrammetric stereo plotting, implements procedural modelling and relies on the availability of overlapping aerial and terrestrial imagery, ground control points and cadastral information. Finally, an application based on the proposed methodology in an urban area in Greece is presented and the future work is discussed.

Multi-scale 3D Modelling of Damaged Cultural Sites: Use Cases and Image-Based Workflows

The creation of 3D models of Cultural Heritage (CH) sites that have undergone a severe disaster due to a catastrophic incident (e.g., earthquake, explosion, terrorist attack) is of great importance for several use cases. Different actors, like Urban Search and Rescue crews, structural, civil and surveying engineers, people in charge of restoration plans, archaeologists, architects, reporters, television presenters and computer engineers, may exploit the 3D information in a different way. Hence, each of them needs models of different scales/levels of detail and under different time constraints. In this paper the need for multi-scale 3D models of severely damaged or collapsed CH sites is addressed and various use cases are discussed. Also, image-based workflows are established for creating multi-scale 3D products via UAV images of a damaged church due to an earthquake. The models of different scales require very different amounts of time for their generation and may be used for search and rescue, damage assessment, geometric documentation, planning of repair works and simple visualization.

3D reconstruction of disaster scenes for urban search and rescue

Natural and man-made disasters that may take place due to a catastrophic incident (e.g., earthquake, explosion, terrorist attack) often result in trapped humans under rubble piles. In such emergency response situations, Urban Search and Rescue (USaR) teams have to make quick decisions under stress in order to determine the location of possible trapped victims. Fast 3D modelling of fully or partially collapsed buildings using images from Unmanned Aerial Vehicles (UAVs) can considerably help USaR efforts, thus improving disaster response and increasing survival rates. The a-priori establishment of a proper workflow for fast and reliable image-based 3D modelling and the a priori determination of the parameters that have to be set in each step of the photogrammetric pipeline are critical aspects that ensure the readiness in an emergency response situation. This paper evaluates powerful commercial and open-source software solutions for the 3D reconstruction of disaster scenes for rapid response situations. The software packages are tested using UAV datasets of a real earthquake scene. A thorough analysis on the parameters of the various modelling steps that may lead to desired results for USaR tasks is made and indicative processing chains are proposed, taking into account the restriction of time. Furthermore, some weaknesses of the data acquisition process that have been detected by performing the experiments are outlined and some improvements and additions are proposed, including an initial preprocessing of the images using a graph-based approach.

Stereo-Orthoimage as a GIS Tool for Reliable Restitution of Cultural Monuments

The use of photogrammetric techniques for the geometric documentation of monuments and archaeological sites is widely known and applied. The basic techniques are: (a) the stereo-restitution, which provides the advantage of 3D observation and accurate digitization but requires specific photogrammetric knowledge and equipment, and (b) the orthophoto, an easy to use raster product that enables the 2D digitization, which is, however, not sufficient for monuments that consist of complex surfaces. The concept of stereo-orthoimage was firstly introduced at the end of the 1960s for cartographic and cadastral applications, combining the advantages of both the orthophoto and 3D observation. This paper analyses the algorithms used for the generation of stereo-orthoimages, presents a developed plugin for the free open-source Geographic Information System QGIS that implements the stereo-orthoimage technique and examines the use of this technique for the restitution and digitization of complex surfaces of monuments for...

Oblique aerial images: a review focusing on georeferencing procedures

ABSTRACT The automatic processing of oblique aerial images is currently one of the most attractive topics in the fields of photogrammetry, remote sensing and computer vision. This kind of images has gained popularity throughout the last years, as it enables depiction of both vertical and horizontal structures of the urban environment, being ideal for various photogrammetric applications, apart from visualization and interpretation purposes. In most cases, the georeferencing of the images is indispensable for their metric exploitation, usually in terms of computation of their camera exterior orientation parameters. For other applications, georeferencing by means of image orthorectification is required, whereas a simple georeferencing in terms of mapping of the center point of the images or the outline of their footprint or image rectification via a 2D transformation also suffices in some cases. However, oblique airborne images pose several challenges in automated georeferencing procedures, due to complex image geometry and strongly varying appearance between images of the same scene taken from different viewing angles. In this paper, a thorough literature review is conducted in order to inform about the recent research in georeferencing of datasets including oblique aerial imagery. The review starts with a classification of oblique aerial imagery and a presentation of the most commonly used camera configurations for oblique imagery acquisition. A brief presentation of their history along with old applications is then made, followed by a categorization of the literature regarding state-of-the-art georeferencing procedures as well as other research trends and applications using oblique aerial images. Then, a more in-depth description of recent research on georeferencing of oblique image datasets is presented. Finally, the significant points, research results and conclusions derived from the literature are discussed, so that they can be utilized by future researchers in the development of georeferencing methods targeted to oblique airborne imagery.

Low Cost Technique for Accurate Geometric Documentation of Complex Monuments by Non-experts

This paper proposes the technique of stereo-orthoimage for reliable and accurate identification and digitization of complex features of cultural heritage (CH) monuments (e.g., edges, outlines, damages, holes, cracks) in the context of large-scale geometric and damage documentation. It is a low cost technique, which can be implemented by non-experts (architects, archaeologists, etc.). A developed plugin, named OrthoSteroMate (OSM), for the open-source GIS system QGIS that implements the stereo-orthoimage technique is presented. It introduces stereo-orthoimages in GIS environments, as complements to conventional orthoimages, allowing better interpretation of the details of built CH and enabling more accurate digitization, taking advantage of stereoscopic observation when no special equipment or photogrammetric knowledge are needed. The application of the plugin along with QGIS tools for the restitution of two CH monuments were made, yielding satisfying results and proving the applicability of the proposed low-cost method for complex CH documentation.

Towards Monuments’ Holistic Digital Documentation: the Saint Neophytos Enkleistriotis Case Study

The expansion of the term “monument” to include the surrounding area of the tangible cultural asset, its natural environment as well as the intangible data relating to its existence and use has gradually resulted the formation of the term “cultural landscapes”. “Monument” has evolved into “monumental place” and a “place with its own soul” and nowadays into a “unity” incorporating the multiple and diversified views which regard the one and single object, the cultural asset. In this paper and through the presented case study of Saint Neophytos Enkleistriotis monument, we attempt to move further on, from the view of the “unity” and the interdiscipilinary approach to the “holistic” view, treating the cultural asset as a “whole”; a “whole” which will have been created from the harmonious merge of all the multifaced entities of which it is comprised.

Exploitation of satellite optical and SAR data for public work studies

This paper studies the use of high resolution satellite optical and SAR images for 1:5,000 mapping production, which is essential for public work and environmental impact assessment studies. The images were used for the extraction of DEMs and their “fit for purpose” use was investigated, through the examination of parameters like accuracy, reliability and performance of morphological features. Orthoimages from satellite optical images using the produced DEMs with or without breaklines were produced. An application was developed on Antiparos island, a Greek island with irregular terrain. The data includes: (a) a triplet of Pleiades (1A, tri-stereo) satellite images, with a resolution of 0.5m, (b) a TanDEM-X Intermediate DEM, a preliminary version of the forthcoming TanDEM-X global DEM, and (c) an accurate DEM produced from the Greek National Cadastre & Mapping Agency S.A. was used as the reference DEM. The georeferencing of the optical images was computed using GCPs which were measured with GNSS. DEMs were extracted using all the possible combinations of the images triplet using automated image matching without any filtering or editing and were evaluated using the reference DEM. The combination of images which yielded the best DEM was then used to manually editing 3D points and collecting breaklines in order to produce a better DEM, which was also evaluated using various statistical measures and geo-morphological features. Orthoimages were created and evaluated using DEMs from optical and SAR data. A discussion about the use of the computed mapping products for the various stages of the public work studies is included.