Search

In recent years 3D building modelling techniques are commonly used in various domains such as navigation, urban planning and disaster management, mostly confined to visualization purposes. The 3D building models are produced at various Levels of Detail (LOD) in the CityGML standard, that not only visualize complex urban environment but also allows queries and analysis. The aim of this paper is to present the methodology and the results of the comparison among two scenarios of LOD2 building models, which have been generated by the derivate UAS data acquired from two flight campaigns in different altitudes. The study was applied in Vrisa traditional settlement, Lesvos island, Greece, which was affected by a devastating earthquake of Mw = 6.3 on 12th June 2017. Specifically, the two scenarios were created by the results that were derived from two different flight campaigns which were: i) on 12th January 2020 with a flying altitude of 100 m and ii) on 4th February 2020 with a flying altitude of 40 m, both with a nadir camera position. The LOD2 buildings were generated in a part of Vrisa settlement consisted of 80 buildings using the footprints of the buildings, Digital Surface Models (DSMs), a Digital Elevation Model (DEM) and orthophoto maps of the area. Afterwards, a comparison was implemented between the LOD2 buildings of the two different scenarios, with their volumes and their heights. Subsequently, the heights of the LOD2 buildings were compared with the heights of the respective terrestrial laser scanner (TLS) models. Additionally, the roofs of the LOD2 buildings were evaluated through visual inspections. The results showed that the 65 of 80 LOD2 buildings were generated accurately in terms of their heights and roof types for the first scenario and 64 for the second respectively. Finally, the comparison of the results proved that the generation of post-earthquake LOD2 buildings can be achieved with the appropriate UAS data acquired at a flying altitude of 100 m and they are not affected significantly by a lower one altitude. [ABSTRACT FROM AUTHOR]

In a post-earthquake scenario, the semantic enrichment of 3D building models with seismic damage is crucial from the perspective of disaster management. This paper aims to present the methodology and the results for the Level of Detail 3 (LOD3) building modelling (after an earthquake) with the enrichment of the semantics of the seismic damage based on the European Macroseismic Scale (EMS-98). The study area is the Vrisa traditional settlement on the island of Lesvos, Greece, which was affected by a devastating earthquake of Mw = 6.3 on 12 June 2017. The applied methodology consists of the following steps: (a) unmanned aircraft systems (UAS) nadir and oblique images are acquired and photogrammetrically processed for 3D point cloud generation, (b) 3D building models are created based on 3D point clouds and (c) 3D building models are transformed into a LOD3 City Geography Markup Language (CityGML) standard with enriched semantics of the related seismic damage of every part of the building (walls, roof, etc.). The results show that in following this methodology, CityGML LOD3 models can be generated and enriched with buildings' seismic damage. These models can assist in the decision-making process during the recovery phase of a settlement as well as be the basis for its monitoring over time. Finally, these models can contribute to the estimation of the reconstruction cost of the buildings. [ABSTRACT FROM AUTHOR]

The contribution of Unmanned Aircraft Systems (UAS, UAV or RPAS) is increasingly acknowledged, researched, tested and applied in a vast variety of fields. Earth Sciences are among the greatest beneficiaries of this development, in terms of having more than an eye in the sky during field work, approaching inaccessible locations and applying Structure from Motion (SfM) methodologies for research in geomorphology, geological mapping, hydrological modeling, mass movement mapping etc. Detailed mapping and evaluation of findings is a critical element of syn- and post-disaster period, for assessing the impacts and their spatial distribution, helping recovery by facilitating aid allocation, coordinating relief efforts, monitoring lifelines status, monitoring of clean-up, and assessing secondary effects or induced hazards. In this paper, the research team summarizes the experience obtained during their involvement in natural disaster mapping of recent (2017-2018) significant catastrophic events in Greece. A survey team equipped with cost effective drones was deployed during and/or after disastrous earthquake, mass movement, flash flood and wildfire events. This resulted in a variety of product types in terms of contribution to post disaster research and emergency management, resulting also in a number of pros and cons in terms of prerequisites and risks of the process. Mapping with drones is essentially field work, and is designed and executed as such. Moreover, it is aviation, so application of strict safety guidelines is a prerequisite. The combination of the two at disaster sites requires technical efficiency, expertise according to the disaster type, team coordination, pilot skills, experience and training, along with a flexible mission risk assessment at all times.Herewith, results of disaster mapping are presented for the earthquake (2017) and mass movements (2017-2018) in Lesvos, the deadly flash floods in West Attica (Mandra, 2017, 2018) and the deadly wildfires in East Attica (Rafina, Mati, 2018). Pros, such as capturing of phenomena dynamics and intact disaster scenery in explicit detail and cons, such as risks, equipment limitations and safety issues are discussed, and some elementary guidelines for the overall process are proposed. Following the cycle of disaster management, the process involves steps to be taken during the pre-disaster phase, the warning/alarm phase, the impact and emergency response phase etc. so that a drone equipped team be readily operational and effective at any given time a disaster occurs. [ABSTRACT FROM AUTHOR]