OBLIQUE MULTI-CAMERA SYSTEMS - ORIENTATION AND DENSE MATCHING ISSUES

International audience3D Optical Metrology (3DOM) unit, Bruno Kessler Foundation (FBK), Trento, Italy <rupnik, franex, remondino>@fbk.eu, http://3dom.fbk.eu Commission III-WG4 ABS TRACT: The use of oblique imagery has become a standard for many civil and mapping applications, thanks to the development of airborne digital multi-camera systems, as proposed by many companies (Blomoblique, IGI, Leica, M idas, Pictometry, Vexcel/M icrosoft, VisionM ap, etc.). The indisputable virtue of oblique photography lies in its simplicity of interpretation and understanding for inexperienced users allowing their use of oblique images in very different applications, such as building detection and reconstruction, building structural damage classification, road land updating and administration services, etc. The paper reports an overview of the actual oblique commercial systems and presents a workflow for the automated orientation and dense matching of large image blocks. Perspectives, potentialities, pitfalls and suggestions for achieving satisfactory results are given. Tests performed on two datasets acquired with two multi-camera systems over urban areas are also reported. Figure 1: Large urban area pictured with an oblique multi-camera system. Once advanced image triangulation methods have retrieved interior and exterior parameters of the cameras, dense point clouds can be deriv ed for 3D city modelling, feature extraction and mapping purposes

Principali tecniche e strumenti per il rilievo tridimensionale in ambito archeologico

The increase of 3D acquisition and modeling techniques applied to archeology is due principally to (i) their capacity to survey archeological artifacts with high precision and a non-contact approach and (ii) the possibility to create 3D digital models useful for data analysis, simulation and preservation. These benefits in terms of knowledge oblige the contemporary archaeologist to acquire a better understanding of 3D acquisition and modeling principles and practice. This evidence arises from the necessity of adopting a common language for experts in 3D data management and archaeologists with the principal aim being the understanding of each other’s requirements and sharing of the purposes of the project. In this article the authors propose a concise but exhaustive explanation of the working principles of active and passive 3D acquisition techniques. For each one a description of instruments and methodologies is developed, pointing out pros and cons of every technique. In conclusion, a sensor fusion approach is presented as an interesting solution to increase the instrument performances while obtaining at the same time a quality improvement of 3D acquisition and modeling results. A final multi-resolution application about Pompeii Forum 3D modeling follows and closes the article

IMAGE ORIENTATION WITH A HYBRID PIPELINE ROBUST TO ROTATIONS AND WIDE-BASELINES

The extraction of reliable and repeatable interest points among images is a fundamental step for automatic image orientation (Structure-From-Motion). Despite recent progresses, open issues in challenging conditions - such as wide baselines and strong light variations - are still present. Over the years, traditional hand-crafted methods have been paired by learning-based approaches, progressively updating the state-of-the-art according to recent benchmarks. Notwithstanding these advancements, learning-based methods are often not suitable for real photogrammetric surveys due to their lack of rotation invariance, a fundamental requirement for these specific applications. This paper proposes a novel hybrid image matching pipeline which employs both hand-crafted and deep-based components, to extract reliable rotational invariant keypoints optimized for wide-baseline scenarios. The proposed hybrid pipeline was compared with other hand-crafted and learning-based state-of-the-art approaches on some photogrammetric datasets using metric ground-truth data. Results show that the proposed hybrid matching pipeline has high accuracy and appeared to be the only method among the evaluated ones able to register images in the most challenging wide-baseline scenarios

Principali tecniche e strumenti per il rilievo tridimensionale in ambito archeologico

The increase of 3D acquisition and modeling techniques applied to archeology is due principally to (i) their capacity to survey archeological artifacts with high precision and a non-contact approach and (ii) the possibility to create 3D digital models useful for data analysis, simulation and preservation. These benefits in terms of knowledge oblige the contemporary archaeologist to acquire a better understanding of 3D acquisition and modeling principles and practice. This evidence arises from the necessity of adopting a common language for experts in 3D data management and archaeologists with the principal aim being the understanding of each other’s requirements and sharing of the purposes of the project. In this article the authors propose a concise but exhaustive explanation of the working principles of active and passive 3D acquisition techniques. For each one a description of instruments and methodologies is developed, pointing out pros and cons of every technique. In conclusion, a sensor fusion approach is presented as an interesting solution to increase the instrument performances while obtaining at the same time a quality improvement of 3D acquisition and modeling results. A final multi-resolution application about Pompeii Forum 3D modeling follows and closes the article

Underwater calibration of dome port pressure housings.

Underwater photogrammetry using consumer grade photographic equipment can be feasible for different applications, e.g. archaeology, biology, industrial inspections, etc. The use of a camera underwater can be very different from its terrestrial use due to the optical phenomena involved. The presence of the water and camera pressure housing in front of the camera act as additional optical elements. Spherical dome ports are difficult to manufacture and consequently expensive but at the same time they are the most useful for underwater photogrammetry as they keep the main geometric characteristics of the lens unchanged. Nevertheless, the manufacturing and alignment of dome port pressure housing components can be the source of unexpected changes of radial and decentering distortion, source of systematic errors that can influence the final 3D measurements. The paper provides a brief introduction of underwater optical phenomena involved in underwater photography, then presents the main differences between flat and dome ports to finally discuss the effect of manufacturing on 3D measurements in two case studies

JOINT ALIGNMENT OF UNDERWATER AND ABOVE-THE-WATER PHOTOGRAMMETRIC 3D MODELS BY INDEPENDENT MODELS ADJUSTMENT

The surveying and 3D modelling of objects that extend both below and above the water level, such as ships, harbour structures, offshore platforms, are still an open issue. Commonly, a combined and simultaneous survey is the adopted solution, with acoustic/optical sensors respectively in underwater and in air (most common) or optical/optical sensors both below and above the water level. In both cases, the system must be calibrated and a ship is to be used and properly equipped with also a navigation system for the alignment of sequential 3D point clouds. Such a system is usually highly expensive and has been proved to work with still structures. On the other hand for free floating objects it does not provide a very practical solution. In this contribution, a flexible, low-cost alternative for surveying floating objects is presented. The method is essentially based on photogrammetry, employed for surveying and modelling both the emerged and submerged parts of the object. Special targets, named Orientation Devices, are specifically designed and adopted for the successive alignment of the two photogrammetric models (underwater and in air). A typical scenario where the proposed procedure can be particularly suitable and effective is the case of a ship after an accident whose damaged part is underwater and necessitate to be measured (Figure 1). The details of the mathematical procedure are provided in the paper, together with a critical explanation of the results obtained from the adoption of the method for the survey of a small pleasure boat in floating condition

MONOCULAR DEPTH PREDICTION IN PHOTOGRAMMETRIC APPLICATIONS

Abstract. Despite the recent success of learning-based monocular depth estimation algorithms and the release of large-scale datasets for training, the methods are limited to depth map prediction and still struggle to yield reliable results in the 3D space without additional scene cues. Indeed, although state-of-the-art approaches produce quality depth maps, they generally fail to recover the 3D structure of the scene robustly. This work explores supervised CNN architectures for monocular depth estimation and evaluates their potential in 3D reconstruction. Since most available datasets for training are not designed toward this goal and are limited to specific indoor scenarios, a new metric, large-scale synthetic benchmark (ArchDepth) is introduced that renders near real-world scenarios of outdoor scenes. A encoder-decoder architecture is used for training, and the generalization of the approach is evaluated via depth inference in unseen views in synthetic and real-world scenarios. The depth map predictions are also projected in the 3D space using a separate module. Results are qualitatively and quantitatively evaluated and compared with state-of-the-art algorithms for single image 3D scene recovery

Integration of range and image data for building reconstruction

The extraction of information from image and range data is one of the main research topics. In literature, several papers dealing with this topic has been already presented. In particular, several authors have suggested an integrated use of both range and image information in order to increase the reliability and the completeness of the results exploiting their complementary nature. In this paper, an integration between range and image data for the geometric reconstruction of man-made object is presented. The focus is on the edge extraction procedure performed in an integrated way exploiting both the from range and image data. Both terrestrial and aerial applications have been analysed for the faade extraction in terrestrial acquisitions and the roof outline extraction from aerial data. The algorithm and the achieved results will be described and discussed in detail

Evaluating tie points distribution, multiplicity and number on the accuracy of UAV photogrammetry blocks

Image orientation is a fundamental task in photogrammetric applications and it is performed by extracting keypoints with hand-crafted or learning-based methods, generating tie points among the images and running a bundle adjustment procedure. Nowadays, due to large number of extracted keypoints, tie point filtering approaches attempt to eliminate redundant tie points in order to increase accuracy and reduce processing time. This paper presents the results of an investigation concerning tie points impact on bundle adjustment results. Simulations and real data are processed in Australis and DBAT to evaluate different affecting factors, including tie point numbers, location accuracy, distribution and multiplicity. Achieved results show that increasing the amount of tie points improve the quality of bundle adjustment results, provided that the tie points are well-distributed on the image. Furthermore, bundle adjustment quality is improved as the multiplicity of tie points increases and their location uncertainty decrease. Based on simulation results, some suggestions for accurate tie points filtering in typical UAV photogrammetry blocks cases are derived