Commission I, WG I/VbKEY WORDS: UAV, Oblique Imagery, photogrammetry, SfM, point clouds, cultural heritage, architectural 3D models ABSTRACT:In recent years, many studies revealed the advantages of using airborne oblique images for obtaining improved 3D city models (e.g. including façades and building footprints). Expensive airborne cameras, installed on traditional aerial platforms, usually acquired the data. The purpose of this paper is to evaluate the possibility of acquire and use oblique images for the 3D reconstruction of a historical building, obtained by UAV (Unmanned Aerial Vehicle) and traditional COTS (Commercial Off-the-Shelf) digital cameras (more compact and lighter than generally used devices), for the realization of high-level-of-detail architectural survey. The critical issues of the acquisitions from a common UAV (flight planning strategies, ground control points, check points distribution and measurement, etc.) are described. Another important considered aspect was the evaluation of the possibility to use such systems as low cost methods for obtaining complete information from an aerial point of view in case of emergency problems or, as in the present paper, in the cultural heritage application field. The data processing was realized using SfM-based approach for point cloud generation: different dense image-matching algorithms implemented in some commercial and open source software were tested. The achieved results are analysed and the discrepancies from some reference LiDAR data are computed for a final evaluation.

Commission I, WG I/VbKEY WORDS: UAV, Oblique Imagery, photogrammetry, SfM, point clouds, cultural heritage, architectural 3D models ABSTRACT:In recent years, many studies revealed the advantages of using airborne oblique images for obtaining improved 3D city models (e.g. including façades and building footprints). Expensive airborne cameras, installed on traditional aerial platforms, usually acquired the data. The purpose of this paper is to evaluate the possibility of acquire and use oblique images for the 3D reconstruction of a historical building, obtained by UAV (Unmanned Aerial Vehicle) and traditional COTS (Commercial Off-the-Shelf) digital cameras (more compact and lighter than generally used devices), for the realization of high-level-of-detail architectural survey. The critical issues of the acquisitions from a common UAV (flight planning strategies, ground control points, check points distribution and measurement, etc.) are described. Another important considered aspect was the evaluation of the possibility to use such systems as low cost methods for obtaining complete information from an aerial point of view in case of emergency problems or, as in the present paper, in the cultural heritage application field. The data processing was realized using SfM-based approach for point cloud generation: different dense image-matching algorithms implemented in some commercial and open source software were tested. The achieved results are analysed and the discrepancies from some reference LiDAR data are computed for a final evaluation.

The geomatic survey in the speleological field is one of the main activities that allows for the adding of both a scientific and popular value to cave exploration, and it is of fundamental importance for a detailed knowledge of the hypogean cavity. Today, the available instruments, such as laser scanners and metric cameras, allow us to quickly acquire data and obtain accurate three-dimensional models, but they are still expensive, require a careful planning phase of the survey, as well as some operator experience for their management. This work analyzes the performance of a smartphone device for a close-range photogrammetry approach for the extraction of accurate three-dimensional information of an underground cave. The image datasets that were acquired with a high-end smartphone were processed using the Structure from Motion (SfM)-based approach for dense point cloud generation: different image-matching algorithms implemented in a commercial and an open source software and in a smartphone application were tested. In order to assess the reachable accuracy of the proposed procedure, the achieved results were compared with a reference dense point cloud obtained with a professional camera or a terrestrial laser scanner. The approach has shown a good performance in terms of geometrical accuracies, computational time and applicability. Appl. Sci. 2019, 9, 3884 2 of 20 solution, and today it is possible to find cheaper and smaller versions, such as profiler [12] and handheld laser scanner devices [13,14]. The active optical sensors [15] allow to directly obtain the spatial position of the detected points, sometimes coupled with the color information; the latter can be recorded by the sensor itself or by an external digital camera integrated into the instrument. These type of instruments have the main advantage of directly and quickly acquiring large amounts of data related to a complex geometry, with a very high accuracy. The raw output data of laser scanner sensors are unstructured point clouds, one for each acquisition point (in the case of a classical laser scanner), which need to be registered in a unique reference system to produce a single point cloud of the scene. Typically, in terrestrial laser scanners (TLS) a mirror rotates vertically and the whole instrument rotates horizontally, allowing a sequential scanning of the scene in both horizontal and vertical directions. There are also handled versions of laser scanners, but they do not always allow for the acquisition of the radiometric information of the object, or they are still very expensive and require some experience, especially in the post-processing of data. These instruments, however, can be easily transported and introduced in restricted access environments [16], but they have limited capabilities when it comes to describing details and edges, which become curved and approximate. Finally, 3D data delivered by active sensors are generally affected by the light and surface characteristics of the scanned materials, by the glass and by specular material...

ABSTRACT:The available sight distance (ASD) in front of the driver to detect possible conflicts with unexpected obstacles is fundamental for traffic safety. In the last 20 years, road design software (RDS) has been continuously updated with dedicated modules to estimate ASD, thus assessing the quality of project from a safety point of view. Unfortunately, the evaluation of ASD still represents an issue in the case of existing road, and the object of discussion in the research community. To avoid problems related to the limitation associated with the use of digital terrain models typically employed in RDS, the Geographic Information Systems (GIS) software can use digital surface models (DSM) which are more flexible in the modelling of sight obstruction due to vegetation, street furniture, and vertical surfaces largely diffused in urbanized areas. The paper deals with the evaluation of GIS in the estimation of ASD in a typical urban road where the density of sight obstruction along the roadside is relatively high. The work explores the case study of a collector road in the city of Turin (Italy). Results confirm the potentiality of GIS software in capturing the complex morphology of the urban environment, thus confirming that GIS could become an important analysis tool for road engineers in the field of road safety. The investigation here described is part of the Pro-VISION Project (funded in 2014 by the Regione Piemonte, Italy).

<p><strong>Abstract.</strong> The advent of new mobile mapping systems that integrate different sensors has made it easier to acquire multiple 3D information with high speed. Today, technological development has allowed the creation of portable systems particularly suitable for indoor surveys, which mainly integrating LiDAR devices, chambers and inertial platforms, make it possible to create in a fast and easy way, full 3D model of the environment. However, the performance of these instruments differs depending on the acquisition context (indoor and outdoor), the characteristics of the scene (for example lighting, the presence of objects and people, reflecting surfaces, textures) and, above all, the mapping and localization algorithms implemented in devices. The purpose of this study is to analyse the results, and their accuracy, deriving from a survey conducted with the KAARTA Stencil 2 handheld system. This instrument, composed of a 3D LiDAR Velodyne VLP-16, a MEMS inertial platform and a feature tracker camera, it is able to realize the temporal 3D map of the environment. Specifically, the acquisition tests were carried out in a context of metrical documentation of an architectural heritage, in order extract architectural detail for the future reconstruction of virtual and augmented reality environments and for Historical Building Information Modeling purposes. The achieved results were analysed and the discrepancies from some reference LiDAR data are computed for a final evaluation. The system was tested in the church and cloister of the Sanctuary of the Beata Vergine del Trompone in Moncrivello (VC) (Italy).</p>