Complex landscapes with high topographic relief and intricate geometry present challenges for complete and accurate mapping of both lateral (x, y) and vertical (z) detail without deformation. Although small uninhabited/unmanned aerial vehicles (UAVs) paired with structure-from-motion (SfM) image processing has recently emerged as a popular solution for a range of mapping applications, common image acquisition and processing strategies can result in surface deformation along steep slopes within complex terrain. Incorporation of oblique (off-nadir) images into the UAV–SfM workflow has been shown to reduce systematic errors within resulting models, but there has been no consensus or documentation substantiating use of particular imaging angles. To address these limitations, we examined UAV–SfM models produced from image sets collected with various imaging angles (0–35°) within a high-relief ‘badland’ landscape and compared resulting surfaces with a reference dataset from a terrestrial laser scanner (TLS). More than 150 UAV–SfM scenarios were quantitatively evaluated to assess the effects of camera tilt angle, overlap, and imaging configuration on the precision and accuracy of the reconstructed terrain. Results indicate that imaging angle has a profound impact on accuracy and precision for data acquisition with a single camera angle in topographically complex scenes. Results also confirm previous findings that supplementing nadir image blocks with oblique images in the UAV–SfM workflow consistently improves spatial accuracy and precision and reduces data gaps and systematic errors in the final point cloud. Subtle differences among various oblique camera angles and imaging patterns suggest that higher overlap and higher oblique camera angles (20–35°) increased precision and accuracy by nearly 50% relative to nadir-only image blocks. We conclude by presenting four recommendations for incorporating oblique images and adapting flight parameters to enhance 3D mapping applications with UAV–SfM in high-relief terrain.

Enhancing UAV–SfM 3D Model Accuracy in High-Relief Landscapes by Incorporating Oblique Images

Three-dimensional digital technology is important in the maintenance and monitoring of cultural heritage sites. This study focuses on using a combination of terrestrial laser scanning and unmanned aerial vehicle (UAV) photogrammetry to establish a three-dimensional model and the associated digital documentation of the Magoksa Temple, Republic of Korea. Herein, terrestrial laser scanning and UAV photogrammetry was used to acquire the perpendicular geometry of the buildings and sites, where UAV photogrammetry yielded higher planar data acquisition rate in upper zones, such as the roof of a building, than terrestrial laser scanning. On comparing the two technologies’ accuracy based on their ground control points, laser scanning was observed to provide higher positional accuracy than photogrammetry. The overall discrepancy between the two technologies was found to be sufficient for the generation of convergent data. Thus, the terrestrial laser scanning and UAV photogrammetry data were aligned and merged post conversion into compatible extensions. A three-dimensional (3D) model, with planar and perpendicular geometries, based on the hybrid data-point cloud was developed. This study demonstrates the potential for using the integration of terrestrial laser scanning and UAV photogrammetry in 3D digital documentation and spatial analysis of cultural heritage sites.

Three-Dimensional Digital Documentation of Cultural Heritage Site Based on the Convergence of Terrestrial Laser Scanning and Unmanned Aerial Vehicle Photogrammetry

Towards a social and context-aware mobile recommendation system for tourism

How smart is e-tourism? A systematic review of smart tourism recommendation system applying data management

The benchmarking of smart e‐tourism data management applications falls under the problem of multicriteria decision‐making (MCDM). This claim is supported by three issues: 12 smart key concepts need to be considered in the evaluation, criteria importance, and data variation among these criteria. Thus, an MCDM solution is essential to overcome problem complexity. To end this, this study presents a decision‐making framework on the basis of the extension of interval type 2 trapezoidal‐fuzzy weighted with zero inconsistency (IT2TR‐FWZIC) integrated with the Vlsekriterijumska Optimizcija I Kaompromisno Resenje (VIKOR) method for evaluating and benchmarking the smart e‐tourism data management applications. Our methodology comprises two consecutive phases. In the first phase, a decision matrix is constructed using the intersection between the 12 key concepts and smart e‐tourism data management applications of each category and subcategory in smart e‐tourism. In the second phase, the integration of the IT2TR‐FWZIC formulation and VIKOR is presented to compute the weights for the 12 key concepts and benchmark the smart e‐tourism data management applications for each category. The results are as follows: (1) A clear difference is found among the criteria weights (12 smart key concepts). Specifically, the real‐time criterion achieves the highest importance weight (0.098), whereas augmented reality obtains the lowest weight (0.068). The context‐awareness and recommender systems have the same weight value (0.087), and the other eight criteria are distributed in between. (2) The smart e‐tourism data management applications are evaluated and benchmarked effectively per category and subcategories. (3) Benchmarked applications in each category are subjected to a systematic ranking in the evaluation process. The sensitivity analysis has shown high correlation outcomes to the systematic ranking results over the 31 scenarios of criteria weight changing. Moreover, a comparative analysis of the proposed work with other existing studies is also discussed.

Interval type 2 trapezoidal-fuzzy weighted with zero inconsistency combined with VIKOR for evaluating smart e-tourism applications

This paper focuses on the processing and study of 3D models obtained from images captured by an unmanned aerial vehicle (UAV). In particular, we wanted to study the accuracy gains achieved in the surveying and the measurement, such as height, area, and volume, of the dimensions of the buildings in the 3D models obtained with both nadir and oblique UAV flights. These latter types of flights are particularly suitable for the 3D modeling of cities or urban agglomerations, where it is important to achieve a complete building reconstruction, including facades and footprints of buildings. For this purpose, several UAV surveys with both nadir and oblique axes were performed. The nadir flight acquired images over an area of about 3.5 hectares containing 30 buildings, while the second flight, performed with both a nadir camera and an oblique camera, was conducted on a single building. The images from the flights were processed with Photoscan software by Agisoft and with Pix4D, studying their different potentialities and functionality. The results were compared with the data from the 1:2000 scale Geotopographic Database (DBGT), with the results of a Global Navigation Satellite System (GNSS) survey and with 3D model from the Terrestrial Laser Scanner (TLS) survey. The obtained results have shown that oblique UAV flights increase the achievable accuracy both in terms of the number of points in a point cloud, and in the in measurements taken on the 3D models, with respect to the limited cost, and at the increase in time for surveying and image processing.

The Use of Nadir and Oblique UAV Images for Building Knowledge

A machine-learning approach to ranking RDF properties

The field of Cultural Heritage has inspired, in the course of last few years, an interest more and more important on behalf of scientific community that deals to survey. The idea that knowledge of a site doesn't apply only to its history but must necessarily include its characteristics of position, shape and geometry, is gathering pace. In Geomatic science the field of cultural heritage benefits to an integrated approach of techniques and different technologies. Every cultural site in fact, is a case in itself, with its own characteristics, problems and specificness. Current techniques offer opportunity to achieve new ways of representation and visualization of cultural site, with the aim of a better metric description. This techniques are powerful tools for analysis of sites and supports to activity of reconstruction and repair. Biggest expectations in this field is laser three-dimensional scanning technique; a system which is able to operate in a methodical way in speed of acquisition and in possibility to access data in real time. Documentation and filing of state of a monument or site is essential in case of reconstruction or conservative project. Possibility to detect very complex geometries with great accuracy allows an in depth study of constructive techniques, making analysis of geometrical details easier which is, with traditional techniques, difficult to achieve. Biggest problems about use of laser scanner survey are graphic outputs for restorers and architects, in fact they often don't know real potential of this techniques, methodologies and functionalities and they expect traditional outputs such as floor plans, cross sections and front elevation of cultural asset. Present study is focused on finding a workflow to support activity of study, restoration and conservative project of cultural heritage, extracting automatically (or with a limited manual operation) graphic outputs from laser scanner survey. Some procedure was tested on two case study the Siviller Castle (XV century), situated in Villasor, a city near Cagliari (Sardinia, Italy) and the tower bell of Mores, near Sassari (Sardinia, Italy). The cultural sites were surveyed with laser scanner Focus 3D by Faro and to process clouds point we were used the JRC 3D Reconstructor software

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Laser scanner survey to cultural heritage conservation and restoration

. The growing interest in recent years in Unmanned Aerial Vehicles (UAVs) by the scientific community, software developers, and geomatics professionals, has led these systems to be used more and more widely, in different fields of engineering and architecture. This is thanks, above all, to their flexibility of use and low cost compared to traditional photogrammetric flights using expensive metric digital cameras or LiDAR sensors. In recent years, UAVs have also been used in the field of monitoring and inspection of public or private buildings that are remarkable in terms of size and architecture. This is mainly due to the focus a sustainability and resource efficiency in the building and infrastructure sector, which aims to extend their lifetimes. Through the use of remote checking using UAVs, the monitoring and inspection of buildings can be brought to a new level of quality and saving. This paper focuses on the processing and study of 3D models obtained from images captured by an UAV. In particular, the authors wanted to study the accuracy gains achieved in the building 3D model obtained with both nadir and oblique UAV flights. The images from the flights were processed using Structure-for Motion-based approach for point cloud generation using dense image-matching algorithms implemented in an open source software. We used the open source software VisualSfM, developed by Chanchang Wu in collaboration with the University of Washington and Google. The dense matching plug-in integrated in its interface, PMVS/CMVS, made by Yasutaka Furukawa, was employed to generate the dense cloud. The achieved results were compare with those gained by Photoscan software by Agisoft and with 3D model from the Terrestrial Laser Scanner (TLS) survey.

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The use of the uav images for the building 3d model generation

. scanner provides the ability to detect the geometric 3D model of a building without any physical contact with the structure. Knowledge of the 3D model will give the opportunity to study the deformation and quantify the damages. Three case studies are presented relating to damaged and/or unsafe buildings: Sivillier Castle (Villasor - Sardinia- Italy), the Bell Tower of Mores (Sardinia-Italy) and industrial building (Cagliari - Italy). The first two cases concern buildings of historical and architectural importance that present a state of compromised conservation; the last, an industrial building compromised by fire. In all cases, a laser scanner survey was carried out that not only provided valuable information but also highlighted structural metric deformation and degradation.

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Andrea Dessi

Papers

The Use of Nadir and Oblique UAV Images for Building Knowledge

A machine-learning approach to ranking RDF properties

Laser scanner survey to cultural heritage conservation and restoration

The use of the uav images for the building 3d model generation

Terrestrial laser scanner for monitoring the deformations and the damages of buildings