132 research outputs found
UAV Photogrammetry and OBIA Classification for Decay Mapping in Built Heritage
No full textOne of the first steps in the development of BIM (Building Information Model) for existing structure is linked to the acquisition and mapping of decay information. Currently, the most widely used practice is visual inspection carried out by experts in the field an based on visual inspection, that requires significant effort in terms of time, human resource and operational costs. To overcome many of the current challenges, the use of Unmanned Aerial Vehicle (UAV) photogrammetry combined with Object-Based Image Analysis (OBIA) techniques represents an innovative approach for non-invasive methodology for decay mapping. The paper presents the results of the integrated approach applied on two case study, differing in types of decay observed and materials. The first involves a building's façade mainly affected by crusts due to washout, and the second concerns a section of a concrete infrastructure, which is affected by different types of surface degradation (cracks, spalling, exposed bars and stains). The results were validated using different approaches in function of the decays observed: in the first case study a cross validation was performed and in the second one a confusion matrix from a ground truth was extracted. The results show satisfactory performance on the OBIA classification in both case study. The methodology developed overcomes some limitations of traditional methods and, the obtained maps, can be integrated in BIM models to enrich the informative content and subsequently support the development of strategies for improving the energy efficiency of the built environment
A New Enhancement Filtering Approach for the Automatic Vector Conversion of the UAV Photogrammetry Output
No full textIn the last decades the photogrammetry has undergone interesting innovation, both in terms of data processing and acquisition mode, to allow obtaining detailed 3D models useful for complete survey and important support for the management and recovery of cultural heritage and buildings. However, despite recent developments, the main photogrammetry outputs are raster data (ortophoto and DEM) and point clouds characterized by high informative content, but they are not typically extracted automatically. Automated feature detection is yet manual, time-consuming procedure and an active area of research. The raster to vector conversion is not direct, but transformations must be performed on the input data to convert the pixel values into features. Always, segmentations are preceded by filter technique to remove noise and to improve the conversion phase. However, remote sensing data and especially UAV photogrammetry output are the most complex to treat because of their heterogeneity (presence of different objects and shapes), the nature of sensor used and the different scale. In this work we experiment new enhancement filter to improve the automatic extraction of vector information for a UAV photogrammetry results of the facing walls of eminent church, symbol of the city of L’Aquila, the” Basilica of Santa Maria di Collemaggio”
Local and Nonlocal Continuum Limits of Ising-Type Energies for Spin Systems
No full textWe study, through a !-convergence procedure, the discrete to continuum limit of
Ising-type energies of the form F"(u) = −Pi,j c" i,juiuj , where u is a spin variable defined on a
portion of a cubic lattice "Zd 8 ⌦, ⌦ being a regular bounded open set, and valued in {−1, 1}. If the
constants c" i,j are nonnegative and satisfy suitable coercivity and decay assumptions, we show that all possible !-limits of surface scalings of the functionals F" are finite on BV (⌦; {±1}) and of the
formR Su'(x, ⌫u) dH11 d−1. If such decay assumptions are violated, we show that we may approximate
nonlocal functionals of the form
R
Su
'(⌫u) dHd−1+ K(x, y)g(u(x), u(y)) dxdy. We focus on the
approximation of two relevant examples: fractional perimeters and Ohta–Kawasaki-type energies. Eventually, we provide a general criterion for a ferromagnetic behavior of the energies F" even when
the constants c" i,j change sign. If such a criterion is satisfied, the ground states of F" are still the uniform states 1 and −1 and the continuum limit of the scaled energies is an integral surface energy of the form above
Free-discontinuity problems generated by singular perturbation: the N-dimensional case
No full textWe provide an approximation of some free discontinuity problems by local functionals with a singular perturbation of higher order
Free-discontinuity problems generated by singular perturbation: the N-dimensional case
No full textWe provide an approximation of some free discontinuity problems by local functionals with a singular perturbation of higher order. More precisely, we study the limiting behaviour of energies of the form F epsilon(u) = 1/epsilon integral(Omega) f(epsilon\del u\(2)) dx + epsilon(2) integral(Omega)\Hu\(2)dx,
where Hu denotes the Hessian matrix of u
MULTISCALE DOCUMENTATION AND MONITORING OF L’AQUILA HISTORICAL CENTRE USING UAV PHOTOGRAMMETRY
No full textNowadays geomatic techniques can guarantee not only a precise and accurate survey for the documentation of our historical heritage
but also a solution to monitor its behaviour over time after, for example, a catastrophic event (earthquakes, landslides, ecc). Europe
is trying to move towards harmonized actions to store information on cultural heritage (MIBAC with the ICCS forms, English
heritage with the MIDAS scheme, etc) but it would be important to provide standardized methods in order to perform measuring
operations to collect certified metric data. The final result could be a database to support the entire management of the cultural
heritage and also a checklist of “what to do” and “when to do it”. The wide range of geomatic techniques provides many solutions to
acquire, to organize and to manage data at a multiscale level: high resolution satellite images can provide information in a short time
during the “early emergency” while UAV photogrammetry and laser scanning can provide digital high resolution 3D models of
buildings, ortophotos of roofs and facades and so on. This paper presents some multiscale survey case studies using UAV
photogrammetry: from a minor historical village (Aielli) to the centre of L’Aquila (Santa Maria di Collemaggio Church) from the
post-emergency to now. This choice has been taken not only to present how geomatics is an effective science for modelling but also
to present a complete and reliable way to perform conservation and/or restoration through precise monitoring techniques, as shown
in the third case study
UAV photogrammetry in the post-earthquake scenario: case studies in L'Aquila
No full textThe main advantage of using the Unmanned Aerial Vehicle (UAV) photogrammetry in a post-earthquake scenario is the ability to completely document the state of the structures and infrastructures, damaged by the earthquake, ensuring the safety of all operators during the data acquisition activities. The safety and accessibility aspect in the area is of crucial concern after an earthquake and sometimes many areas may be inaccessible, but, at the same time, it is necessary to collect data in order to monitor and evaluate the damage. The development of new algorithms in the field of Computer Vision drastically improved the degree of automation of the 3D point clouds generation using the photogrammetry techniques. In addition, data acquisition techniques using the UAV allow a complete 3D model with the highest possible resolution especially with respect to the conventional satellite or aerial photogrammetry to be produced. These advantages make the UAV photogrammetry highly suitable for surveys in a geo-hazard context as in a post-earthquake scenario. Some results from surveys carried out with the UAV photogrammetry after L'Aquila Earthquake occurred in 2009 will be presented and discussed
Finite difference approximation of energies in Fracture Mechanics
No full textWe provide a variational approximation by finite-difference energies of
functionals of the type
defined for u E SBD(Q), which are related to variational models in ’ fracture
mechanics for linearly-elastic materials. We perform this approximation in di-
mension 2 via both discrete and continuous functionals. In the discrete scheme we
treat also boundary value problems and we give an extension of the approximation
result to dimension 3
Free-discontinuity problems generated by singular perturbation
No full textWe show that some free discontinuity problems can be obtained as a limit of nonconvex local functionals with a singular perturbation of higher order
Automatic shoreline detection from eight-band VHR satellite imagery
No full textCoastal erosion, which is naturally present in many areas of the world, can be significantly increased by factors such as the reduced transport of sediments as a result of hydraulic works carried out to minimize flooding. Erosion has a significant impact on both marine ecosystems and human activities; for this reason, several international projects have been developed to study monitoring techniques and propose operational methodologies. The increasing number of available high-resolution satellite platforms (i.e., Copernicus Sentinel) and algorithms to treat them allows the study of original approaches for the monitoring of the land in general and for the study of the coastline in particular. The present project aims to define a methodology for identifying the instantaneous shoreline, through images acquired from the WorldView 2 satellite, on eight spectral bands, with a geometric resolution of 0.5mfor the panchromatic image and 1.8mfor the multispectral one. A pixel-based classification methodology is used to identify the various types of land cover and to make combinations between the eight available bands. The experiments were carried out on a coastal area with contrasting morphologies. The eight bands in which the images are taken produce good results both in the classification process and in the combination of the bands, through the algorithms of normalized difference vegetation index (NDVI), normalized difference water index (NDWI), spectral angle mapper (SAM), and matched filtering (MF), with regard to the identification of the various soil coverings and, in particular, the separation line between dry and wet sand. In addition, the real applicability of an algorithm that extracts bathymetry in shallow water using the "coastal blue" band was tested. These data refer to the instantaneous shoreline and could be corrected in the future with morphological and tidal data of the coastal areas under study
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