Documentation of heritage buildings using close-range UAV images: dense matching issues, comparison and case studies

International audienceThree-dimensional (3D) documentation of heritage buildings has long employed both image-based and range-based techniques. Unmanned aerial vehicles (UAVs) provide a particular advantage for image-based techniques in acquiring aerial views, which are difficult to attain using classical terrestrial-based methods. The technological development of optical sensors and dense matching algorithms also complement existing photogrammetric workflows for the documentation of heritage objects. In this paper, fundamental concepts in photogrammetry and 3D reconstruction based on structure from motion (SfM) will be briefly reviewed. Two case studies were performed using two types of UAVs, one being a state-of-the-art platform dedicated to obtaining close-range images. Comparisons with laser scanning data were performed and several issues regarding the aerial triangulation and dense matching results were assessed. The results show that although the dense matching of these UAV images may generate centimetre-level precision, a further increase in precision is often hampered by the quality of the onboard sensor

A Robotized Raspberry-Based System for Pothole 3D Reconstruction and Mapping

Repairing potholes is a task for municipalities to prevent serious road user injuries and vehicle damage. This study presents a low-cost, high-performance pothole monitoring system to maintain urban roads. The authors developed a methodology based on photogrammetry techniques to predict the pothole's shape and volume. A collection of overlapping 2D images shot by a Raspberry Pi Camera Module 3 connected to a Raspberry Pi 4 Model B has been used to create a pothole 3D model. The Raspberry-based configuration has been mounted on an autonomous and remote-controlled robot (developed in the InfraROB European project) to reduce workers' exposure to live traffic in survey activities and automate the process. The outputs of photogrammetry processing software have been validated through laboratory tests set as ground truth; the trial has been conducted on a tile made of asphalt mixture, reproducing a real pothole. Global Positioning System (GPS) and Geographical Information System (GIS) technologies allowed visualising potholes on a map with information about their centre, volume, backfill material, and an associated image. Ten on-site tests validated that the system works in an uncontrolled environment and not only in the laboratory. The results showed that the system is a valuable tool for monitoring road potholes taking into account construction workers' and road users' health and safety

Guidelines for Best Practice and Quality Checking of Ortho Imagery

For almost 10 years JRC's ¿Guidelines for Best Practice and Quality Control of Ortho Imagery¿ has served as a reference document for the production of orthoimagery not only for the purposes of CAP but also for many medium-to-large scale photogrammetric applications. The aim is to provide the European Commission and the remote sensing user community with a general framework of the best approaches for quality checking of orthorectified remotely sensed imagery, and the expected best practice, required to achieve good results. Since the last major revision (2003) the document was regularly updated in order to include state-of-the-art technologies. The major revision of the document was initiated last year in order to consolidate the information that was introduced to the document in the last five years. Following the internal discussion and the outcomes of the meeting with an expert panel it was decided to adopt as possible a process-based structure instead of a more sensor-based used before and also to keep the document as much generic as possible by focusing on the core aspects of the photogrammetric process. Additionally to any structural changes in the document new information was introduced mainly concerned with image resolution and radiometry, digital airborne sensors, data fusion, mosaicking and data compression. The Guidelines of best practice is used as the base for our work on the definition of technical specifications for the orthoimagery. The scope is to establish a core set of measures to ensure sufficient image quality for the purposes of CAP and particularly for the Land Parcel Identification System (PLIS), and also to define the set of metadata necessary for data documentation and overall job tracking.JRC.G.3-Agricultur

Introduction to applied photogrammetry and cartography for civil engineering

Los ingenieros civiles, a lo largo de sus carreras, deberían manejar información cartográfica, que se obtiene principalmente mediante técnicas de fotogrametría. Este trabajo tiene como objetivo prácticamente introduciendo la técnica de fotogrametría aérea digital, con el propósito de compartir los métodos utilizados para obtener la cartografía para planificar su trabajo. La formulación matemática no está dentro del alcance de este trabajo, ya que, en mi opinión, tiene poco que aportar a los ingenieros civiles y existen tratados muy complejos destinados a lectores más especializados en el campo. Este breve texto comienza por delinear algunos conceptos básicos de cartografía, centrándose en sistemas de referencia, que están cambiando hoy en día y deberían ser conocidos por civiles ingenieros antes de trabajar con datos cartográficos. La parte fundamental del texto se centra en la fotogrametría digital, y al enfatizar una vez más, en su simplicidad, pretende explicar, desde mi experiencia profesional, todo el proceso de trabajo desde el momento en que se solicita un vuelo fotogramétrico hasta la cartografía digital llega a las manos de los ingenieros para trabajar en ella, con sus precisiones y precisiones. Por lo tanto, este trabajo está destinado a proporcionar ayuda a los profesionales de ingeniería civil cuando evaluar y manejar datos cartográficos que, en mayor o menor grado, ser la base de su trabajo.Civil engineers, throughout their careers, should handle cartographical information, which is mainly obtained by photogrammetry techniques. This work aims at practically introducing the digital aerial photogrammetry technique, with the purpose of sharing the methods used to obtain cartography to plan their work. Mathematical formulation is not under the scope of this work, since, in my view, it has little to contribute to civil engineers and there exist very complex treaties aimed at more specialised readers in the field. This short text begins by outlining some basic cartography concepts, focusing on reference systems, which are changing nowadays and should be known by civil engineers before working with cartographical data. The text’s fundamental part focuses on digital photogrammetry, and by emphasizing once again on its simplicity, it aims at explaining, from my professional experience, all the work process from the moment when a photogrammetric flight is requested until digital cartography arrives into the hands of engineers to work on it, with its accuracies and precisions. Therefore, this work is intended to provide help to civil engineering professionals when valuating and handling cartographical data which, to a greater or lesser degree, would be the basis for their work

Using Linear Features for Aerial Image Sequence Mosaiking

With recent advances in sensor technology and digital image processing techniques, automatic image mosaicking has received increased attention in a variety of geospatial applications, ranging from panorama generation and video surveillance to image based rendering. The geometric transformation used to link images in a mosaic is the subject of image orientation, a fundamental photogrammetric task that represents a major research area in digital image analysis. It involves the determination of the parameters that express the location and pose of a camera at the time it captured an image. In aerial applications the typical parameters comprise two translations (along the x and y coordinates) and one rotation (rotation about the z axis). Orientation typically proceeds by extracting from an image control points, i.e. points with known coordinates. Salient points such as road intersections, and building corners are commonly used to perform this task. However, such points may contain minimal information other than their radiometric uniqueness, and, more importantly, in some areas they may be impossible to obtain (e.g. in rural and arid areas). To overcome this problem we introduce an alternative approach that uses linear features such as roads and rivers for image mosaicking. Such features are identified and matched to their counterparts in overlapping imagery. Our matching approach uses critical points (e.g. breakpoints) of linear features and the information conveyed by them (e.g. local curvature values and distance metrics) to match two such features and orient the images in which they are depicted. In this manner we orient overlapping images by comparing breakpoint representations of complete or partial linear features depicted in them. By considering broader feature metrics (instead of single points) in our matching scheme we aim to eliminate the effect of erroneous point matches in image mosaicking. Our approach does not require prior approximate parameters, which are typically an essential requirement for successful convergence of point matching schemes. Furthermore, we show that large rotation variations about the z-axis may be recovered. With the acquired orientation parameters, image sequences are mosaicked. Experiments with synthetic aerial image sequences are included in this thesis to demonstrate the performance of our approach