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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.

ABSTRACT:During archaeological excavations it is important to monitor the new excavated areas and findings day by day in order to be able to plan future excavation activities. At present, this daily activity is usually performed by using total stations, which survey the changes of the archaeological site: the surveyors are asked to produce day by day draft plans and sections which allow archaeologists to plan their future activities. The survey is realized during the excavations or just at the end of every working day and drawings have to be produced as soon as possible in order to allow the comprehension of the work done and to plan the activities for the following day. By using this technique, all the measurements, even those not necessary for the day after, have to be acquired in order to avoid a 'loss of memory'. A possible alternative to this traditional approach is aerial photogrammetry, if the images can be acquired quickly and at a taken distance able to guarantee the necessary accuracy of a few centimeters. Today the use of UAVs (Unmanned Aerial Vehicles) can be considered a proven technology able to acquire images at distances ranging from 4 m up to 20 m: and therefore as a possible monitoring system to provide the necessary information to the archaeologists day by day. The control network, usually present at each archaeological site, can give the stable control points useful for orienting a photogrammetric block acquired by using an UAV equipped with a calibrated digital camera and a navigation control system able to drive the aircraft following a pre-planned flight scheme. Modern digital photogrammetric software can solve for the block orientation and generate a DSM automatically, allowing rapid orthophoto generation and the possibility of producing sections and plans. The present paper describes a low cost UAV system realized by the research group of the Politecnico di Torino and tested on a Roman villa archaeological site located in Aquileia (Italy), a well-known UNESCO WHL site. The results of automatic orientation and orthophoto production are described in terms of their accuracy and the completeness of information guaranteed for archaeological site excavation management.

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.

Highlights:• The paper aims to validate UAV photogrammetry as a very flexible tool for archaeological areas; a fix wing eBee device by Sensefly is tested.• Derived DSM and aerial orthoimages in complex areas with different formal traits are discussed, targeting high mansory ruins and collapsed parts.• Up to 2 cm accuracy and high resolution 3D models are convenient to extract morphological data. Abstract:Unmanned aerial vehicle (UAV) photogrammetry has shown a very rapid development in many fields, especially in archaeological excavation areas and architectural complexes, where it offers a detailed generation of three-dimensional (3D) data including the possibility of updating over time. It also proves to be a very flexible tool applicable to many types of complex areas with a variety of different features. The use of aerial acquisition provides highly effective results, adding to both rapid capture and lower costs. In fact, today in the field of archaeological research, great efforts are invested in the generation of very large-scale models and orthophotos, and the technology seems to promise further future developments, not only from the terrestrial (orthogonal) point of view, but also from the nadiral direction from a low altitude, as a preferential and often optimal point of view. Here an effective workflow for photogrammetric product generation is presented for selected case studies in some monumental areas of ancient Hierapolis in Phrygia (Turkey), in which the Italian Archaeological Mission of Hierapolis (MAIER) has been working since the 1960s. The recent experiences achieved by UAV photogrammetry are quite innovative. The variety and complexity of the buildings, as well as the height of their ruins, offer numerous challenges, which are interesting to deal with. The 3D aerial survey was performed for multiple purposes with the eBee system by Sensefly. Specific attention was paid to the digital surface model (DSM) and aerial orthoimages of three test areas: the Plutonium area; the Thermal Bath-Church; and the Necropolis. Starting from the same technical approach, a comparative assesment among the three sites was carried out, taking into account the specific goals, the type of the structure and the terrain conformation.Keywords: unmanned aerial vehicle (UAV); digital surface model (DSM); aerial photogrammetry; archaeological heritage; 3D modelling; data integration Resumen:La fotogrametría con vehículos aéresos no tripulados (Unmanned Aerial vehicle, UAV) ha mostrado un desarrollo muy rápido en muchos campos, especialmente en áreas de excavación arqueológica y complejos arquitectónicos, donde ofrece una detallada generación de datos tridimensionales (3D), junto con su actualización en el tiempo. También demuestra ser una herramienta muy flexible aplicable en muchos tipos de áreas complejas, con diferentes características formales. El uso de la toma aérea proporciona hoy resultados altamente efectivos, lo que aumenta la rapidez de adquisición y menores costes. De hecho, hoy en día en el campo de la investig...