Charalabos Ioannidis

Towards a strategy for control of suburban informal buildings through automatic change detection

The problem of informal settlements is of significant importance and has similar causes worldwide. In Greece, such buildings are relatively well built and number nearly 1,000,000 across the country. This social and economic issue requires a combined approach. In this paper, a proposed solution to this problem is developed at a technical and administrative level, taking into consideration the criteria of least possible cost and maximum benefit from usage of modern technology. The basic idea is the development of a system that allows for periodic, automatic monitoring and detection of new buildings. With additional field control applied only to specific locations, immediate detection of informal construction projects prior to completion is enabled, at which time measures to halt their development can be more easily taken. The suggested procedure is based on the use of high resolution images and the application of automatic change detection by computation and comparison of digital surface models and building extraction techniques. Results from a pilot application of the proposed procedure are given together with an estimated cost for application of this method to the coastal zone of eastern Attica, a Greek prefecture with many existing and emerging informal constructions.

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.

Selective 4D modelling framework for spatial-temporal land information management system

This paper introduces a predictive (selective) 4D modelling framework where only the spatial 3D differences are modelled at the forthcoming time instances, while regions of no significant spatial-temporal alterations remain intact. To accomplish this, initially spatial-temporal analysis is applied between 3D digital models captured at different time instances. So, the creation of dynamic change history maps is made. Change history maps indicate spatial probabilities of regions needed further 3D modelling at forthcoming instances. Thus, change history maps are good examples for a predictive assessment, that is, to localize surfaces within the objects where a high accuracy reconstruction process needs to be activated at the forthcoming time instances. The proposed 4D Land Information Management System (LIMS) is implemented using open interoperable standards based on the CityGML framework. CityGML allows the description of the semantic metadata information and the rights of the land resources. Visualization aspects are also supported to allow easy manipulation, interaction and representation of the 4D LIMS digital parcels and the respective semantic information. The open source 3DCityDB incorporating a PostgreSQL geo-database is used to manage and manipulate 3D data and their semantics. An application is made to detect the change through time of a 3D block of plots in an urban area of Athens, Greece. Starting with an accurate 3D model of the buildings in 1983, a change history map is created using automated dense image matching on aerial photos of 2010. For both time instances meshes are created and through their comparison the changes are detected.

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.

Deep convolutional neural networks for building extraction from orthoimages and dense image matching point clouds

Abstract. Automatic extraction of buildings from remote sensing data is an attractive research topic, useful for several applications, such as cadastre and urban planning. This is mainly due to the inherent artifacts of the used data and the differences in viewpoint, surrounding environment, and complex shape and size of the buildings. This paper introduces an efficient deep learning framework based on convolutional neural networks (CNNs) toward building extraction from orthoimages. In contrast to conventional deep approaches in which the raw image data are fed as input to the deep neural network, in this paper the height information is exploited as an additional feature being derived from the application of a dense image matching algorithm. As test sites, several complex urban regions of various types of buildings, pixel resolutions and types of data are used, located in Vaihingen in Germany and in Perissa in Greece. Our method is evaluated using the rates of completeness, correctness, and quality and compared with conventional and other “shallow” learning paradigms such as support vector machines. Experimental results indicate that a combination of raw image data with height information, feeding as input to a deep CNN model, provides potentials in building detection in terms of robustness, flexibility, and efficiency.

Modelling of Static and Moving Objects: Digitizing Tangible and Intangible Cultural Heritage

From the ancient library of Alexandria 2300 years ago, cultural collections have a common fundamental base; to gather, preserve and promote knowledge helping the intellectual and cognitive evolution of humanity. Nowadays the information revolution has given scientists, educators, researchers and individuals the ability not only to use a variety of digital libraries as a source of information but also to contribute to these libraries by uploading data that they create, leading to a massive production of digital data that we need to verify, manage, archive, preserve and reuse. Cultural heritage (CH) data is a category in digital libraries that needs our attention the most, because of their crucial role in helping us to interact with the past and learn, promote and preserve our cultural assets. Digital documentation of tangible and intangible heritage, data formats and standards, metadata and semantics, linked data, crowdsourcing and cloud, the use and reuse of data and copyright issues are the rising challenges that we try to address in this chapter, through literature research and best practice examples. At the end of this analysis, this chapter tries to predict the future of Digital Heritage Libraries, where 3D digital assets will be part of augmented, virtual and mixed reality experiences.

LIDAR vs dense image matching point clouds in complex urban scenes

This study aims to highlight the differences, in terms of robustness and efficiency, of the use of LIDAR point clouds compared to dense image matching (DIM) point clouds at urban areas that contain buildings with complex structure. The application is conducted over an area in the Greek island of Milos using two different types of data: (a) a dense point cloud which extracted by DIM using a variation of the stereo-method semi-global matching (SGM) at RGB digital aerial images, and (b) a georeferenced LIDAR point cloud. For the case of the DIM point cloud, the following steps were applied: aerial triangulation, rectification of the original images to epipolar images, extraction of disparity maps and application of a 3D similarity transformation. The evaluations that were executed included urban and rural areas. At first step, a direct cloud-to-cloud comparison between the georeferenced DIM and LIDAR point clouds was carried out. Then, the corresponding orthoimages generated by the DIM and LIDAR point clouds undergo a quality control. Although the results show that the LIDAR point clouds respond better at such complex scenes compared to DIM point clouds, the latter gave promising results. In this context, the Quality Assurance issue is also discussed so as to be more efficient towards the challenge of the increasingly greater demands for accurate and cost effective applications.

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.

Mapping of Building Materials and Consevation Interventions Using GIS: The Case of Sarantapicho Acropolis and Erimokastro Acropolis in Rhodes

The geometric documentation of characteristic parts of the walls of the Sarantapicho Acropolis and Erimokastro Acropolis in Rhodes, Greece, in accordance with GIS modeling and analysis operations are utilized to accomplish the mapping of building materials, decay patterns and conservation interventions of both investigated sites. Ortho-rectified images as base-maps and the building materials and decay data, comprised the spatial and attribute data sets. Building materials and decay data were collected after the application of non-destructive testing and evaluation techniques in situ and analytical techniques in lab after sampling. The result was the development of thematic maps of building materials and decay. Moreover, using geoprocessing analysis the thematic map of conservation interventions was produced incorporating attribute data from both building materials and decay themes. This multidisciplinary approach provides the basis for the compatibility assessment of conservation interventions (whenever a...