UAV platforms are nowadays a valuable source of data for inspection, surveillance, mapping and 3D modeling issues. New applications in the short-and close-range domain are introduced, being the UAVs a low-cost alternatives to the classical manned aerial photogrammetry. Rotary or fixed wing UAVs, capable of performing the photogrammetric data acquisition with amateur or SLR digital cameras, can fly in manual, semi-automated and autonomous modes. With a typical photogrammetric pipeline, 3D results like DSM/DTM, contour lines, textured 3D models, vector data, etc. can be produced, in a reasonable automated way. The paper reports the latest developments of UAV image processing methods for photogrammetric applications, mapping and 3D modeling issues. Automation is nowadays necessary and feasible at the image orientation, DSM generation and orthophoto production stages, while accurate feature extraction is still an interactive procedure. New perspectives are also addressed. Figure 1: Example of scenes surveyed with a UAV system (Microdrone MD4-200) and photogrammetric results achieved from the acquired images: digital surface model, orthoimages and overlaid contours (archaeological area in Montalcino, Italy).

In this paper an automated methodology is presented (i) to orient a set of close‐range images captured with a calibrated camera, and (ii) to extract dense and accurate point clouds starting from the estimated orientation parameters. The whole procedure combines different algorithms and techniques in order to obtain accurate 3D reconstructions in an automatic way. The exterior orientation parameters are estimated using a photogrammetric bundle adjustment with the image correspondences detected using area‐ and feature‐based matching algorithms. Surface measurements are then performed using advanced multi‐image matching techniques based on multiple image primitives. To demonstrate the reliability, precision and robustness of the procedure, several tests on different kinds of free‐form objects are illustrated and discussed in the paper. Three‐dimensional comparisons with range‐based data are also carried out.

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ABSTRACT:The HBIM of the Basilica di Collemaggio in L'Aquila is part of the restoration project of the building seriously damaged by the earthquake in 2009. The project "Ripartire da Collemaggio", funded by ENIservizi, involves an interdisciplinary group called to work together toward a common goal: the need of security of the structures and the need of conservation of the architectonic value of the Basilica. Starting from the photogrammetric and laser scanning survey, interpretation and modelling were needed to create a detailed HBIM to manage the phases of analysis, simulation of structural behavior, economic evaluation of the project, and final restoration. This paper described the generation of the HBIM and its use in the on-going restoration project with a particular attention to the procedures used to preserve the complexity given by photogrammetric and laser scanning data.

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This paper presents an innovative procedure to create parametric building information modelling (BIM) objects from point clouds of complex architectural features. BIM technology requires an advanced parametric representation of the geometry involving spatial relationships, constraints and material properties. The aim of the procedure is a BIM-based reconstruction methodology that preserves the level of detail encapsulated in photogrammetric and laser-scanning point clouds, and relies on non-uniform rational basis splines (NURBS) curves. The particular case of architectural objects with irregular shapes is addressed due to the lack of commercial BIM software able to handle such buildings. An actual case study made up of 7Á5 billion points is discussed to demonstrate the use of the proposed procedure with huge point-cloud datasets.

Abstract:A new 3D acquisition and processing procedure to map RGB, thermal IR and near infrared images (NIR) on a detailed 3D model of a building is presented. The combination and fusion of different data sources allows the generation of 3D thermal data useful for different purposes such as localization, visualization, and analysis of anomalies in contemporary architecture. The classic approach, which is currently used to map IR images on 3D models, is based on the direct registration of each single image by using space resection or homography. This approach is largely time consuming and in many cases suffers from poor object texture. To overcome these drawbacks, a "bi-camera" system coupling a thermal IR camera to a RGB camera has been setup. The second sensor is used to orient the "bi-camera" through a photogrammetric network also including free-handled camera stations to strengthen the block geometry. In many cases the bundle adjustment can be executed through a procedure for automatic extraction of tie points. Terrestrial laser scanning is adopted to retrieve the 3D model building. The integration of a low-cost NIR camera accumulates further radiometric information on the final 3D model. The use of such a sensor has not been exploited until now to assess the conservation state of buildings. Here some interesting findings from this kind of analysis are reported. The paper shows the methodology and its experimental application to a couple of buildings in the main Campus of Politecnico di Milano University, where IR thermography has previously been carried out for conservation and maintenance purposes. OPEN ACCESS

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